Aplicacion Tecnica - Paper N°4 - Circuit Breakers inside LV Switchboards (Ingles)(1SDC007103G0201)

4December 2006 Technical Application Papers ABB circuit-breakers inside LV switchboards 1SDC007103G0201 ���������������������������� ABB circuit-breakers inside LV switchboards Index Introduction .............................................. 2 1 Problems of overheating inside switchboards 1.1 1.2 1.3 1.4 General aspects ...................................... 3 The current carrying capacity ................. 3 Verification of temperature-rise by test (in compliance with IEC 60439-1) ........................................... 4 Verification of temperature-rise by extrapolation ........................................... 7 3 Problems concerning shortcircuit 3.1 Main definitions of the parameters characterizing a switchboard under short-circuit conditions ......................... 39 3.1.1 General prescriptions and information about short-circuit withstand strength ......................... 39 3.2 Prescriptions concerning the electrical circuits of a switchboard....................... 40 3.2.1 Main busbar systems ......................................... 40 3.2.2 Distribution busbars and conductors derived by the main busbars ................................................ 41 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards 2.1 Power loss inside switchboards ............. 9 2.1.1 Internal structure .................................................. 9 2.1.2 Tipology of the circuit-breaker installed ............... 9 2.1.3 Cross-section of conductors within switchboards ...................................................... 11 2.1.4 Paths of the current ........................................... 15 3.3 Reduction of the possibility of short-circuit events and of the relevant effects ......... 42 3.3.1 Minimum anchor distances for conductors........ 42 3.3.2 Verification of the short-circuit withstand strength and of the current limiting characteristics of the circuit-breakers................................................... 45 3.3.3 Problems concerning the installation distances 46 Annex A: Example of electrical switchboards with ABB circuit-breakers ..................................................... 48 Annex B: Forms of internal separation ................................. 50 Annex C: Degrees of protection (IP code)............................. 51 Glossary ................................................................ 52 2.2 Dissipation of the heat generated inside switchboards .............................. 16 2.2.1 Switchboard ventilation ...................................... 16 2.2.2 Side surfaces and positioning of switchboards .....16 2.2.3 Forms of internal separation of switchboards .... 17 2.2.4 Degree of protection of switchboards ................ 17 2.3 Dissipation of the heat generated in the terminals .............................................. 17 2.3.1 Problems linked to convection .......................... 17 2.3.2 Problems linked to conduction .......................... 20 2.3.3 Current carrying capacity of circuit-breakers and busbars ...................................................... 22 1 ���������������������������� Introduction An electrical switchboard is the combination of more protection and switching devices assembled in one or more adjacent compartments. A switchboard is formed by the compartment, which the Standards name “enclosure” (with support and mechanical protection functions for the different components enclosed), and the electrical equipment, constituted by the apparatus, the internal connections and the incoming and outgoing terminals for the connection to the installation. This Technical Paper is intended to deal in detail with the equipment in the switchboard, providing the reader with the basic information necessary to choose the circuitbreakers to be installed inside low voltage switchboards in the easiest and most correct way, paying particular attention to ABB SACE range of products. After a quick survey of the main product Standards concerning switchboards and circuit-breakers, IEC 60439-1 and IEC 60947-2 respectively, the main problems which a manufacturer has to face when designing a switchboard are analyzed. This Technical Paper is divided into three main parts dealing with the problems of overheating in switchboards, general prescriptions to improve the current carrying capacity of the circuit-breakers inside enclosures and the problems caused by short-circuit in switchboards 1 1 Introduction The product Std. IEC 60439-1 applies to low voltage and controlgear assemblies, the rated voltage of which does not exceed 1000 Va.c. at frequencies not exceeding 1000 Hz, or 1500 Vd.c.; the product Std. IEC 60947-2 applies to circuit-breakers, the main contacts of which are intended to be connected to circuits, the rated voltage of which does not exceed 1000 Va.c. or 1500 Vd.c. 2 ABB circuit-breakers inside LV switchboards 1 Problems of overheating inside switchboards 1.1 General aspects One of the main problems which makes difficult the identification of the correct typology of circuit-breakers to be installed inside a switchgear or controlgear assembly is calculating the maximum continuous current which the circuit-breaker can carry without damages or premature ageing according to the service temperature. The total freedom of the manufacturer in designing switchboards using components different for number, position and dimensions makes the installation conditions of the same circuit-breaker so different that it results impossible to determine exactly its “maximum current carrying capacity” which, affected by peculiar operating conditions, results different from that defined by the manufacturer and referred to standard conditions. Figure 1 Figure 1a 1 Problems of overheating inside switchboards 1.2 The current carrying capacity Now we shall take into consideration how the concept of current carrying capacity is dealt with in the different Standards, in particular, in the product Standard concerning circuit-breakers and in that one regarding low-voltage switchgear and controlgear assemblies. The circuit-breakers, according to the prescriptions of the European Low Voltage Directive 2006/95/CE, are manufactured and tested in compliance with the product Std. IEC 60947-2 “Low-voltage switchgear and controlgear – Part 2: Circuit-breakers”. - the carrying capacity is verified by connecting the circuit-breakers with conductors having size (maximum) and length (minimum) as specified in the relevant Standard this means that the standard conditions are referred also to the connection modalities of the circuit-breaker - the carrying capacity is verified by ensuring that during the test, the maximum temperature-rise limits admitted on the different parts of the circuitbreaker are not exceeded such temperature-rise, not meant as absolute temperature, but as a temperature difference expressed in Kelvin, are referred to an ambient air temperature of 40°C. The circuit-breakers are generally installed inside enclosures which have different functions; among these the following : - making inaccessible to people the connections of the different apparatus (if not for voluntary actions); - giving a place to house the circuit-breakers where steady positioning is guaranteed; - ensuring an adequate protection against ingress of solid foreign objects and ingress of water. These enclosures are called controlgear and switchgear assemblies (hereafter referred to as assemblies) and comply with the specific product Std. IEC 60439-1 “Lowvoltage switchgear and controlgear assemblies – Part 1: Type-tested (TTA) and partially type-tested assemblies (PTTA)” However, the installation conditions inside an assembly differ from the conditions specified by the Std. IEC 60947-2, which are the verification conditions of a circuitbreaker current carrying capacity in free air. The conditions inside the switchboard (wiring, separations, arrangement of the different apparatus) force the circuitbreaker to operate under conditions characterized by the following aspects: As regards the verification of the current carrying capacity in uninterrupted duty (Iu), the Std. IEC 60947-2 states the conditions of the test performance. Here are the main requirements to be met : - the current carrying capacity shall be verified in free-air the Std. IEC 60947-1 “Low-voltage switchgear and controlgear - Part 1: General rules” specifies in detail what is meant by “free air”: “Free air is understood to be air under normal indoor conditions (indoor conditions are understood to be not the conditions inside switchgear or controlgear assemblies or enclosures, but the conditions inside buildings or similar environments), reasonably free from draughts and external radiation” therefore, no external radiations (e.g. those due to the sun’s rays-Figure 1) or draughts which are not caused simply by the natural convective motion originated by heating (Figure 1a) are admitted. ABB circuit-breakers inside LV switchboards 3 with an air ambient temperature around the circuitbreaker depending on the assembly design and on the devices it houses.if a rated diversity factor fn<1 is present (not all the loads are supplied with 100% of their rated current) the switchboard circuits are tested at a current value lower than the rated one at full load. but to the “equipment” meant as a combination of one or more protection and switching apparatus equipped with any possible switching. without the appropriate evaluations. it is possible to have assemblies with complex forms of internal separations (Figure 2). or assemblies with forced ventilation or air-conditioned assemblies Figure 2 preclude the need for additional tests on circuit-breakers incorporated in assemblies.the circuits of the switchboard shall be tested at a current which is equal to the rated current multiplied by the rated diversity factor fn. for example in accordance with IEC 60439-1.���������������������������� . also of the air temperature inside it. measuring. After these considerations. As a consequence. mounted and wired with internal electrical and mechanical connections. . this Standard deals with the rated current of the single electrical circuit and not with the rated current of the individual components. cross-sections depending on the rated current of the circuits are imposed by the Standard. For further information about correlated subjects.not in free air. This current shall be carried out without the temperaturerise of the various parts of the assembly exceeding the limits specified when the test is performed in accordance with prescriptions of the Standard itself. such as circuit-breakers or conductors.the circuit-breakers are connected through conductors of size and length stated by the manufacturer . protection and setting. making reference to the current carrying capacity. In particular. of their disposition and application. the test shall be carried out on those circuits which allow the heaviest temperature-rise conditions to be reproduced. as a consequence. IEC 60947-2. reference shall be made to the indications given in the Standard itself. relevant to the low voltage circuit-breakers. understood as the ratio between the maximum value of the sum of the currents flowing through all the main circuits considered. 1 Problems of overheating inside switchboards 1. states that in normal service the current carrying capacities may differ from the test values. as regards the general test conditions. and the sum of the rated currents of the same circuits Itest = InC x fn . reminds that the prescribed tests do not The product Std. IEC 60439-1 concerning low voltage controlgear and assemblies does not refer to the individual components present. however. IEC 60947-1. which in the performance prescriptions regarding temperaturerise. it is evident that the conditions leading the manufacturer to define a rated uninterrupted current for a single circuit-breaker are different from the conditions under which the circuit-breaker shall be used inside an assembly. From the prescriptions above it results that: . the different degree of protection and the modality of arrangement of the assembly in the environment cause a modification of the amount of heat exchanged towards the outside of the assembly and.3 Verification of temperature-rise by test (in compliance with IEC 60439-1) . Besides.if no d etailed information about the external conductors to be used under normal operating conditions are known. the rated current of a circuit is defined by the switchboard manufacturer as a function of the ratings of the electrical components of the circuit.if the switchboard is cabled with conductors having a cross-section reduced with respect to that prescribed 4 ABB circuit-breakers inside LV switchboards . on the different installation conditions and on the size of the connected conductors. depending. for example. This concept is also recalled in the Std. at any moment. it is obvious that the current carrying capacity of circuit-breakers determined in compliance with the relevant product Standard cannot be considered equal to their carrying capacity when they are installed inside an assembly. but with particular prescriptions regarding air circulation in particular. consequently. The performance modalities of the temperature-rise test include two main prescriptions: . In accordance with the definition. also the Std. IEC 60439-1 (updating of Annex A1 Circuit-breakers can be defined as built-in components and therefore they must comply with the prescriptions of the product Standards.8 fn=0. the absolute temperature values T T (expressed in °C) at which the different parts of the assembly operate are determined and. Figure 3 Parts of assemblies Built in components For example conventional switchgear and controlgear. Table 1 below shows the temperature-rise limits and the relevant remarks of the Std.8 fn=0.mechanical strength of conducting material. the rated current of a circuit is not that assigned. with reference to an average ambient temperature TA lower than or equal to 35 °C. For the different components of assemblies. rectifier bridge and printed circuit). a maximum temperature of 105K shall not be exceeded for bare busbars and copper conductors so that the mechanical strength of conducting material is guaranteed. parts of equipment (e.permissible temperature limit of the insulating materials in contact with the conductor. in a switchboard. taking into consideration the temperature in the assembly.by the Standard and used in the test. but it is determined by considering the assigned diversity factor.the effect of the temperature of the conductor on the apparatus connected to it. temperature-rise higher than the maximum acceptable values measured in the test might occur during normal operations. dated March 2005) which are valid when the temperaturerise test is carried out in compliance with the prescriptions of the Standard itself. In accordance with these test conditions. 30K 40K 40K 50K 15K 25K Therefore.for plug-in contacts. electronic subassemblies (e. it is evident that ABB circuit-breakers inside LV switchboards 5 . When the terminals of the built-in components are also the terminals for the external insulated conductors the lowest temperature-rise limits shall be applied. regulator. or a part of the switchboard. is tested by “applying” simultaneously to all the circuits a test current equal to the assigned rated current multiplied by “fn”. However. By assuming that all the other mentioned criteria have been fulfilled. Table 1 1 Problems of overheating inside switchboards The following numerical example has the purpose of making clear what explained above. Reference is made to the switchboard of Figure 3. the manufacturer assigns the rated current for the load circuits and assigns a rated diversity factor “fn” to the enclosure to be tested. 70K An assembly used or tested under installation conditions may have connections. whose loads are cabled with the same conductors through which it is put into service. the switchboard.8 fn=0.g. Under these conditions. . Terminals for external insulated conductors Temperature-rise (values or prescriptions) In accordance with the relevant requirements for the individual components. IG I2 C I3 B A D E I4 Busbars and conductors. . nature and surface treatment of the contact material. IEC 60439-1 must not be exceeded. stabilized power supply unit. . the temperature-rise limits �T = (TT – TA) imposed by the Std. operational amplifier).g. the type.8 fn=0. plug-in contacts of removable or withdrawable parts which connect to busbars I1 I5 I6 I7 Limited by: .8 fn=0. nature and disposition of which will not be the same as those adopted for the test and a different temperature rise of terminals may result and may be required or accepted. . I2 = 160A I3 = 400A I4 = 250A I5 = 630A I6 = 160A I7 = 400A fn=0.possible effects on adjacent equipment. or in accordance with the manufacturer’s instructions.8 I2test= 128A I3test = 320A I4test = 200A I5test = 504A I6test = 128A I7test = 320A Manual operating means: accessible with closed assembly of metal of insulating material accessible with open assembly of metal of insulating material Accessible external enclosures and covers: which need to be touched during normal operation of metal of insulating material which need to be touched during normal operation of metal of insulating material Discrete arrangements of plug and socket type connection 40K 50K Determined by the limits of those components of the equipment of which they form part. and the temperaturerise limits for a circuit-breaker installed inside a LV switchboard recalculated for a reference ambient temperature TA = 35°C. it can be deduced that the maximum permissible temperature is TT = (ΔT + TA) = 120°C. which. must comply with the most demanding or restricting prescription of the two product Standards. Table 3 and Figure 5 show the maximum acceptable temperature-rise and temperature limits for the different parts of the assemblies as stated by the switchboard Standard. To make clear this concept. the maximum temperature-rise limit of the switchboard terminals for insulated external connections is 70K and consequently the maximum operating temperature is 105°C. in this case 70°C . Table 2 and figure 4 hereunder show the indications concerning temperature-rise limits given in the Std. As a summary of the above. consequently equal to 85°C. allows the manufacturer to state for Figure 5 Connection with busbar 6 ABB circuit-breakers inside LV switchboards . Table 3 Parts of assembliesdescription Terminal for external insulated connections (IEC 60439-1) Terminals for external connections (IEC 60947-2) Manual operating means: Accessible with enclosed assembly of metal of insulating material Accessible only with open assembly of metal of insulating material 30K 40K 65 °C 75 °C 15K 25K 50 °C 60 °C Temperature-rise limits 70K 85K Temperature limits (starting from TA =35°C) 105 °C 120 °C 1 Problems of overheating inside switchboards Parts intended to be touched but not gripped: Parts which need not to be touched during normal operation: Figure 4 Parts intended to be touched but not gripped: (CEI EN 60439-1) of metal of insulating material 30K 40K 65 °C 75°C Accessible parts which need not to be touched during normal operation (IEC 60439-1): of metal of insulating material 40K 50K 75°C 85°C Non-accessible parts which need not to be touched during normal operation (IEC 60947-2): of metal of insulating material 55K 65K 90°C 100°C Connection with PVC-insulated cable From Table 2 it results how for a circuit-breaker in freeair the accepted temperature-rise on the terminals is ΔT=80K. therefore. with the comments reported for the built-in components (circuit-breakers are components of the switchboard).���������������������������� circuit-breakers and in particular some parts of them (e. it is the prescription for the terminals of the circuit-breaker component which determines the maximum operating temperature. When the connection to the terminals is realized through PVC insulated conductors. and Table 1. by difference. in accordance with the comments reported in Table 1. accessible parts and operating means) can be also considered in all respects as part of controlgear or switchgear assemblies.g. In particular this applies to the terminals where external insulated conductors are connected. taking as reference an ambient temperature TA = 40°C. On the contrary. it can be obtained that the maximum temperature-rise limit is equal to 85K. thus. if the connection to the circuit-breaker is constituted by bare copper busbars. Table 2 Parts of assembliesdescription Terminals Manual operating means: parts of metal parts of insulating material parts of metal parts of insulating material parts of metal parts of insulating material 25K 35K 40K 50K 50K 60K 65 °C 75 °C 80 °C 90°C 90°C 100°C Temperature-rise limits 80K Temperature limits (starting from TA =40°C) 120 °C the circuit-breaker terminals a maximum temperature of 120°C. a reference ambient temperature of 35°C shall be considered. The prescriptions regarding temperature-rise defined by the switchboard Standard instead refer to an average ambient temperature TA = 35°C. IEC 60947-2 for circuit-breakers considered as an individual component in free-air. If the circuit-breaker is installed inside a switchboard. whose maximum operating temperature is 105°C. it is the temperature of the cable component to determine the maximum acceptable temperature on the terminals. then the suggested calculation method can be used without running into errors.the equipment installed is designed for direct current or alternating current up to and including 60 Hz. . the crosssection of the air outlet openings is at least 1. The following data are needed to calculate the temperature-rise of the air inside an enclosure: . . The calculation validity is limited by a series of initial assumptions: .effective power loss of equipment.presence and dimensions of ventilation openings. .where the enclosures with external ventilating openings have compartments. the mere knowledge of the temperature of the air around the circuit-breakers would not allow the calculation of the current carrying capacity.number of internal horizontal partitions.type of installation of the enclosure (exposed. Starting from the required input data. However. To carry out an analysis of temperature-rise in accordance with this calculation method. it is possible to verify if the components which are in a certain position are suitable to operate at that temperature or if they need to be replaced by other components. with reference to circuit-breakers.there is an approximately even distribution of power losses inside the enclosure.1 times the cross-section of the air inlet openings. ABB SACE offers its free software program OTC. As regards the analysis of the suggested calculation methods..conductors carrying high currents and structural parts are so arranged that eddy current losses are negligible. . covered. To this purpose. . etc. if the minimum dimensions of the connections suggested by ABB (see Tables 16 and 17 at page 21) are complied with. As regards the above.). it shall be taken into account that the calculation method suggested by IEC/TR 60890 is a conservative one which generally results into values higher than those which can be verified in reality. . The method proposed allows temperature-rise to be determined inside PTTA enclosures without forced ventilation.geometric dimensions (height/width/depth). OTC interface 1 Problems of overheating inside switchboards 7 ABB circuit-breakers inside LV switchboards . with the total of supply currents not exceeding 3150 A. busbars.there are no more than three horizontal partitions in the assembly or in a section of it. .1. Once the temperature of the air at the different heights of the enclosure is known. cables and connections. the power losses of all the components are calculated correctly and the results thus obtained are integrated with the manufacturer’s experience.the installed equipment is so arranged that air circulation is but little impeded..for enclosures with ventilation openings. .. this program calculates the temperature of the air at different heights of the enclosure through a dedicated interface which appears as in the figure below. ABB SACE gives a derating of the current carrying capacity as a function of the temperature of the air around the circuit-breaker: thus it becomes possible to calculate if the carrying capacity admitted for the circuit-breaker at the temperature calculated at its installation point results to be higher than the current of the supplied load. As a consequence it is possible to state that.4 Verification of temperature-rise by extrapolation The Standard regarding low voltage controlgear and switchgear assemblies provides that temperaturerise verification for the PTTA type can be carried out also by extrapolation making specific reference to the prescriptions given in IEC/TR 60890 “A method of temperature-rise assessment by extrapolation for partially type-tested assemblies (PTTA) of low-voltage switchgear and controlgear”. . the surface of the ventilating openings in each horizontal partition shall be at least 50% of the horizontal cross-section of the compartment. the reader is required to consult the Standard itself. . Figure 7 Connection busbar In its turn. . In enclosures with a degree of protection not very high or with ventilation openings. A switchboard can be considered as an enclosure housing a series of elements generating heat and able to dissipate heat towards the outside. with the air inside the switchboard (convection) and with the walls of the switchboard itself (radiation) as shown in Figure 6. The elements generating heat inside the enclosure exchange heat between them (conduction). This chapter analyses the main elements which contribute to generate and influence the temperature inside a switchboard and tries to give some useful information for their optimization with the purpose of decreasing the temperature and consequently of reducing the derating of the current carrying capacity of circuit-breakers. .the dissipation of the heat produced by the terminals. .the dissipation of the heat produced inside the enclosure. affect temperature at each point of the enclosure itself and of each component installed inside it. the enclosure exchanges heat towards the external environment.���������������������������� 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards In order to give the necessary indications on the methods intended to improve the current carrying capacity of the circuit-breakers inside switchboards. assembly). part of the heat is exchanged through a real air circulation between the assembly and the external environment. These elements are: . together with the structure of the enclosure.the power loss inside the enclosure. as shown in Figure 7. first of all it is necessary to analyze an assembly from a thermodynamic point of view. Also this heat exchange occurs by conduction (through the cables connected to the 8 ABB circuit-breakers inside LV switchboards Switchboard wall 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Figure 6 Conduction Circuit-breaker Air outside the enclosure Air inside the enclosure Heat Connection busbar Heat Convection Circuit-breaker Heat Connection busbar Radiation Circuit-breaker All these phenomena of circulation and exchange of internal and external air. convection and radiation. To make this evaluation easier. No.45% 55% . From these data. a modification of the temperature may be caused by a power loss due to the current flow. on the contrary. the total induction is not null. Now. if each conductor is enclosed by a single ring (Figure 8a). together with the measures to be taken in order to reduce the power loss and limit its effects. Figure 9 Support in amagnetic material Bars Insulator For a correct assessment of the power losses it is necessary to take into consideration also the configuration of the separation form: in fact. the typology of the circuit-breaker installed.1. As the tables below show. If the system structure is such as to create a closed configuration embracing the conductors. Table 4 shows the percentage value representing the part of losses developing inside the enclosure related to the power loss inside the conductor bars. Figure 8 Figure 8a 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards No induction Ferromagnetic meterial of the separation form Current induction 2. it results that the increase of the rated current and consequently the number of busbars in parallel per phase and the material used for the separation of the conductor bars may considerably affect heating. ABB SACE offers some tables which are reported below and refer to moldedcase circuit-breakers of Tmax series (Table 5) and air circuit-breakers type Emax (Table 6) respectively.1. The same phenomenon occurs in the bus ducts between the enclosure and the conductor bars. the power loss of the same circuit-breaker varies depending both on its version as well as on the type of protective release installed.1 Internal structure The material used to realize structure and partitions inside switchboards is often ferromagnetic and conductive.65% 15% . currents shall result into null induction. As an example to illustrate the influence of this phenomenon.1 Power loss inside switchboards As known. of phases 3 3 3 Crosssection [mm] 100x10 100x10 100x10 In [A] 1000 3000 3000 Material of the encasement (of the bus duct) ferromagnetic ferromagnetic amagnetic (aluminum) ABB circuit-breakers inside LV switchboards 9 . with the consequent circulation of induced current. the cross-sectional area of the internal conductors of the switchboard. and the current paths. Joule-effect losses due to eddy currents and hysteresis losses are induced. the different components which constitute the main power sources and which consequently represent also heat sources inside a switchboard shall be considered in detail. of busbars in parallel per phase 1 3 3 Losses inside the enclosure (% referred to the total loss inside the conductor bars) 35% .2 Typology of the circuit-breaker installed Circuit-breakers are components of switchboards which cannot be disregarded when calculating total power loss.20% One pole bars 2. as Figure 8 shows (or all the four conductors in a system with the neutral conductor). the sum of the Table 4 No. therefore it is important that the formation of close rings is prevented by the insertion of insulators or anchor clamps made of amagnetic and/or insulating material (see Figure 9). if a ferromagnetic ring embraces all the three conductors of a three-phase system. with consequent local heating of remarkable importance. power loss and therefore heat generation. These elements are: the internal structure.2. Terminals Also the mechanical fixing of conductors could cause this inconvenient. 4 23.5 1. The difference between the power loss of a circuit-breaker in three-pole version compared with a four-pole version is not considered.4 64.8 90 96 150 115 125 15 36 57.8 7 10.4 21 32.9 90 141 231 27 66 105.6 13.9 36 90 144 225 351.9 15.3 25.3 18.6 3.���������������������������� Taking reference to these two variables.5 6.7 84 160.2 32.5 3.3 9.8 11.1 6.1 1.8 8.1 2.2 60 92 93 117 119 PR221 PR222 PR223 5.5 123 53.3 7.1 7.5 24 51 1.4 6 6.the power losses of the circuit-breakers equipped with thermo-magnetic releases are higher than those of the circuit-breakers with electronic releases.1 13.2 9 10.4 16.7 4.7 15 4.9 14.7 7.8 3.2 29. it is possible to observe that : .3 3. since in a normal circuit the current flowing in the neutral conductor is assumed to be null.1 52.1 11.5 3 10.8 15.1 12.3 8 10 12.6 30 44.4 62.8 11.6 53.5 47.2 5.8 2 2.3 15 17.2 52.7 93 110. it is advisable to use circuit-breakers in fixed version and equipped with electronic type releases.7 28.7 12.L F W F T7 V W TMF TMD TMA MF MA 1.8 19.4 20.1 45 10.the power losses of withdrawable circuit-breakers are higher than those of the fixed ones .9 18 43.9 F: fixed Table 6 W: withdrawable P: plug-in Total (3/4 poles) power loss [W] In=630 In=800 In=1000 In=1250 In=1600 In=2000 In=2500 In=3200 In=4000 In=5000 In=6300 F: fixed X1B-N F 41 65 102 159 260 W 63 100 157 257 400 X1L F 50 80 125 196 W 87 140 219 342 E1B-N F 65 96 150 253 W 95 147 230 378 E2B-N-S F 29 45 70 115 180 W 53 83 130 215 330 F E2L W E3N-S-H-V F 22 38 60 85 130 205 330 W 36 58 90 150 225 350 570 F E3L W E4S-H-V F W E6H-V F W 105 170 165 265 215 335 330 515 235 360 425 660 170 265 415 650 290 445 700 1100 W: withdrawable 10 ABB circuit-breakers inside LV switchboards .1 9.H.5 8.6 12 27.5 5.5 36 51 T2 P 5.3 7.5 7.1 12.9 4.8 11.3 4.6 18.8 58.8 3.8 49. Table 5 Total (3/4 poles) power loss [W] Releases In [A] 1 1.8 15 18 21.8 40.5 86.6 2 2.8 8.6 22.6 10.3 17.4 9.8 72 31.4 21.5 12.8 6 8.9 8.9 165 258 423 24 60 96 150 234.7 39.7 10.8 6.1 60 F T3 P Under heavy conditions from a thermal point of view.7 13.5 16 20 25 32 40 50 63 80 100 125 160 200 250 320 400 500 630 800 10 25 63 100 160 250 320 400 630 800 1000 1250 1600 T11P F T1 F F 4.4 15.9 14.7 41.2 11.2 4 5 6.3 4.1 10. 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards T4 F P/W F T5 P/W F T6 W T7 S.7 9 10.1 12.6 27 37.5 8.8 23. 6 4.0 3.9 2.8 Diam. IEC/TR 60890 includes a series of tables which give the power loss of cables and busbars inside switchboards per unit length.3 W/m 1.1 W/m 0.20 0.1 2.4 0.9 8.6 0.5 0.5 7.6 3.1 1.4 1.3 2.0 - 1) Any arrangement desired with the values specified referring to six cores in a multi-core bundle with a simultaneous load 100% 2) single length power losses 2) ABB circuit-breakers inside LV switchboards 11 .0 2.12 0.7 0. Here is an example to show how the contribution of the connection cables is fundamental for a correct assessment of the total power loss of the components inside the switchboard.3 1.9 1.7 5.4 10.2 5.6 0.3 1.00 A 2.1 1.2 1.8 1.6 11.3 Cross-section of the conductors within switchboards In primary distribution switchboards.5 0. 1) d d d d Air temperature inside the enclosure around the conductors 35 °C 55 °C 35 C 55 °C 35 °C 55 °C operating current operating current operating current operating current operating current operating current power losses 2) power losses 2) power losses 2) power losses 2) power losses 2) mm2 1.7 1.2 5.1 3.8 6.4 Conductors for auxiliary circuits mm2 0.6 0.9 1.8 1.3 1.14 0.1.9 3. whereas they are often not considered since they are not “strictly” part of the switchboard.8 9.5 2.9 12.7 6.3 7.3 2.4 2.6 A 12 20 25 32 50 65 85 115 150 175 225 250 275 350 400 460 W/m 2.3 7.6 5.2 3. making reference to the current carrying capacity.3 4.6 0.6 1.7 5.9 3.8 0.7 A 8 11 14 18 25 34 W/m 0. the power loss of the connection systems (busbars/cables) is usually from 20% to 40% of the total power loss of the switchboard.5 2.7 4.30 0.9 17.5 0.6 2.4 8.1 3. By applying these tables (here defined as Tables 7 – 8 – 9) it is possible to point out how a reduction in the power loss corresponds to an increased cross-section. Table 7: Operating current and power losses of insulated conductors Section (Cu) Maximum permissible conductor temperature 70 °C 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards In addition.1 1.3 2.0 6.2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300 A 12 17 22 28 38 52 W/m 2.3 8.22 0.9 2. 0.4 1.7 15.50 0.1 4.4 3.7 10.34 0.8 0.2 1.9 10.8 A 1.4 15. it is important to remark how the cables entering the enclosure give a contribution not negligible to power loss.5 3.4 3.1 3.2 A 8 12 18 23 31 42 55 67 85 105 125 147 167 191 225 260 W/m 0.56 0.2 2.2 7.1 3.7 11.5 9.5 3.75 1.4 3.6 2.9 11.9 11.6 6.4 3.4 4.4 8.1 2.9 1.7 9.8 1.6 3.0 5.3 1.5 A 8 12 20 25 32 50 65 85 115 149 175 210 239 273 322 371 W/m 0.6 0.2 9.3 11.8 5.9 1.7 4.0 13. The Std.2 8.2 7.6 A 12 20 25 32 48 64 85 104 130 161 192 226 275 295 347 400 W/m 2.1 4.5 0.4 6.8 3. 0 18.9 27.9 72.2 169.9 A* 105 124 157 157 198 266 414 317 368 556 468 694 566 826 667 955 858 1203 1048 1445 1688 W/m 10.2 85.6 492 482 17.2 34.0 7.3 41.7 25.5 A** 105 124 162 172 198 284 532 338 402 780 532 1032 655 1280 780 1524 1032 1920 1280 2180 2400 12 x 2 23.1 20 x 10 199 25 x 5 124 30 x 5 149 30 x 10 299 40 x 5 199 40 x 10 399 50 x 5 249 50 x 10 499 60 x 5 299 60 x 10 599 80 x 5 399 80 x 10 799 100 x 5 499 100 x 10 999 120 x 10 1200 *) one conductor per phase 82 5.0 19.9 42.1 202 115 6.8 53.7 37.4 26.1 36.8 19.1 98.3 41.5 32.0 *) one conductor per phase **) two conductors per phase 1) single length Table 9: Operating current and power losses of bare conductors used as connections between the apparatus and the main busbars Width x Thickness Crosssection (Cu) Maximum permissible conductor temperature 65 °C Air temperature inside the enclosure around the conductors 35 °C 50 Hz to 60 Hz ac and dc operating current operating current operating current power losses 1) power losses 1) Air temperature inside the enclosure around the conductors 55 °C 50 Hz to 60 Hz ac and dc operating current power losses 1) power losses 1) W/m 4.5 59.3 14.5 21.5 36.5 21.0 100.1 20.4 121.4 36.3 53.3 A* 144 170 215 215 271 364 569 435 505 770 644 968 782 1164 926 1357 1200 1742 1476 2128 2514 W/m 19.8 18.2 960 348 12.8 72.7 61.8 72.6 7.6 39.1 44.5 83.4 40.0 29.4 6.9 14.8 54.1 62.6 85.7 34.8 12.1 68.3 55.1 27.5 29.8 69.0 164.9 32.4 2680 1848 68.5 20 x 3 59.2 116.8 648 253 10.2 55.2 1560 1560 58.0 9.7 1256 1256 45.4 38.7 60.5 20 x 2 39.9 19.1 38.4 11.6 117.1 140.3 34.7 805 805 28.4 150 124 7.3 14.6 61.4 64.6 77.9 84.3 44.1 20.1 1848 648 22.3 8.7 69.5 11.7 55.4 47.8 50.9 73.1 199 124 149 299 199 399 249 499 299 599 399 799 499 999 1200 A* 144 170 215 215 271 364 568 435 504 762 641 951 775 1133 915 1310 1170 1649 1436 1982 2314 W/m 19.2 42.1 101.8 9.5 5.9 94.8 29.6 A** 177 206 274 258 338 487 807 572 656 1048 586 1310 989 1562 1154 1814 1484 1756 1756 2803 3288 W/m 14.3 50.9 24.7 77.1 26.4 26.5 48.1 7.7 22.7 22.4 60.4 15.9 35.7 16.6 11.4 99.9 35.9 45.8 18.9 82.7 16.3 46.7 16.5 20 x 5 99.5 21.5 80.2 35.7 34.9 130 96 6.4 4.4 61.8 90.4 44.2 49.7 85.6 55.4 11.3 30.0 249 218 9.7 1245 413 14.3 9.6 29.9 34.5 18.0 61.6 mm x mm mm2 A* W/m A** W/m 7.5 15 x 3 44.0 57.5 88.8 21.5 80.9 A** 242 282 375 354 463 668 1107 78 899 1436 1128 1796 1357 2141 1583 2487 2035 3165 2407 3844 4509 W/m 27.0 61.8 47.2 44.8 18.7 23.6 43.7 413 288 11.6 29.8 648 648 22.1 26.0 52.9 5.6 A* 105 124 157 157 198 266 415 317 369 562 469 706 570 849 675 989 875 1271 1077 1552 1833 W/m 10.3 90.8 86.8 74.3 52.9 189.7 23.4 6.���������������������������� Table 8: Operating current and power losses of bare conductors.8 94.2 50.5 36.5 99.5 38.9 36.2 960 960 34.6 18.8 2432 805 29.6 15.5 32.3 2928 **) two conductors per phase 1) single length 12 ABB circuit-breakers inside LV switchboards power losses 1) .9 57.0 28.9 45.0 19.3 41.9 36.5 A** 242 282 375 351 463 665 1097 779 894 1410 1112 1716 1322 2008 1530 2288 1929 2806 2301 3298 3804 W/m 27.8 69.1 54.3 69.2 11.2 5.5 47.9 102.4 101.8 116.7 32.5 15.7 6.3 62.5 29.9 28. without direct connections to the apparatus Width x Thickness Crosssection (Cu) Maximum permissible conductor temperature 85 °C Air temperature inside the enclosure around the conductors 35 °C 50 Hz 60 Hz ac operating current operating current dc and ac to 16 2/3 Hz operating current operating current operating current Air temperature inside the enclosure around the conductors 55 °C 50 Hz 60 Hz ac operating current dc and ac to 16 2/3 Hz operating current operating current 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards power losses 1) power losses 1) power losses 1) power losses 1) power losses 1) power losses 1) power losses 1) mm x mm 12 x 2 15 x 2 15 x 3 20 x 2 20 x 3 20 x 5 20 x 10 25 x 5 30 x 5 30 x 10 40 x 5 40 x 10 50 x 5 50 x 10 60 x 5 60 x 10 80 x 5 80 x 10 100 x 5 100 x 10 120 x 10 mm2 23.0 28.4 7.6 15.6 12.5 54.9 10.5 1560 492 17.5 8.9 53.3 21. in vertical arrangement.2 116.6 60.5 15 x 2 29.7 16.7 102.5 8.9 348 348 12.9 184 152 8.4 42.0 18.1 27.7 137.5 29.5 44.3 12.3 54.6 115.4 23.5 39.2 16.0 29.6 12.3 13.6 55.1 29.1 38.8 8.0 28.8 40.5 22.5 A** 177 206 274 256 338 485 800 568 652 1028 811 1251 964 1465 1116 1668 1407 2047 1678 2406 2774 W/m 14.8 85.4 32.7 115.7 63.9 64.5 27.5 36.8 4.7 A* 69 88 102 93 125 174 284 204 233 402 284 532 338 660 402 780 532 1032 660 1280 1524 W/m 4.5 32.0 21.4 103.4 138.2 187.0 52. the contribution to the load current in terms of power loss of the individual circuit-breaker and the total power loss are reported in the following table: Table 10 Circuit-breaker IG I1 I2 I3 I4 I5 E2 1600 EL T5 400 EL T5 400 EL T5 400 EL T3 250 TMD T3 250 TMD In CB [A] 1600 400 400 400 250 250 Ib [A] 1340 330 330 330 175 175 Power loss [W] 80. the structure and the relevant singlewire diagram. according to the type of apparatus installed inside the switchboard.Example This example has the purpose of evaluating – as first approximation – the total power loss inside the switchboard of which Figure 10 shows the arrangement of the components.7 33. busbars and cables. Figure 10 Switchboard front A I1 B IG C I2 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards L Number of horizontal partitions = 0 Wall-mounted separated enclosure H Dimensions H W [mm] [mm] 2000 1440 D [mm] 840 P D I3 E I4 F I5 Single-wire diagram IG I1 I2 I3 I4 I5 The components which form the switchboard are circuit-breakers.7 33. the power loss can be determined on the basis of the dissipated power “Pn ” at the rated current “InCB” (see previous Tables 5 and 6) referred to the current which really flows through the circuitbreaker “Ib” (full load current of the circuit). the dimensions.2 26.2 234 Total power loss of the circuit-breakers [W] ABB circuit-breakers inside LV switchboards 13 . The formula linking these three quantities is the following : PCB = PnCB x (Ib / InCB)2 Then. Circuit-breakers As regards circuit-breakers.7 33.7 26. The power loss is calculated for each component and then the total power loss is determined. 4 19 13.8 1.8 332 Total power loss of the connection busbars [W] Then. with reference to the typology.���������������������������� Busbars As regards main busbars.0 1.150 0. the effective power loss can be determined from the dissipated powers.150 Ib [A] 1340 330 330 330 175 175 Power loss [W] 54 3.0 2. the same method used for the busbars can be applied and the relevant results are reported in Table 12.6 68 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Total power loss of the connection busbars [W] Cables As regards cables. as shown in the previous Tables 8 and 9.2 45.150 0.8 Ib [A] 1340 330 330 330 175 175 Power loss [W] 133. the total power dissipated inside the switchboard is given by the sum of the three contributions already determined above.1 0. taking reference to Table 8 above. at the nominal current and per unit length. distribution busbars and the busbars connecting circuit-breakers and cables. the length “L” and the load current of the busbars installed inside the switchboard. the contribution in terms of power loss of the single length and the total power loss are reported in Table 11 below: Table 11 Connection busbar IG I1 I2 I3 I4 I5 Cross-sectional area nx[mm]x[mm] 2x60x10 30x10 30x10 30x10 20x10 20x10 Length [m] 0.7 1. therefore: PTQ = 234+68+332=784W It is important to note how the total power loss would be equal to 452W and therefore the estimated temperature would be much lower than the effective one if the cable contribution (332W) were not taken into account. The formula to relate the data in the table to the characteristics (load current and length) of the busbars installed in the switchboard is the following: PSB = PnSB (Ib/InSB)2 x 3 x LSB Therefore.150 0.8 64.8 3.8 3. 14 ABB circuit-breakers inside LV switchboards .9 55.150 0.4 1.6 1. Tabella 12 Cable IG I1 I2 I3 I4 I5 Cross-sectional area [n]xmm2 4x240 240 240 240 120 120 Length [m] 1.450 0. Figure 11 Suggested positioning: The highest current (500 A) flows through the shortest path 50 A In case of switchboards with many columns. Thus. by dividing the current into the two branches of the switchboard busbar system. which is a solution implying the circulation of highest currents.4 Paths of the current The positioning of apparatus and conductors may result into a different power loss inside the switchboard. the dissipated power inside the switchboard is reduced and unquestionable advantages from the thermal point of view are achieved.1.2. a remarkable reduction in the power loss is obtained – with the same cross-section – in comparison with a configuration having the incoming feeder at both ends of the switchboard as in Figure 12a. Thus. contrary to what occurs in a type of installation as that of Figure 11a. in barycentric position with respect to the load distribution. so that the paths of the highest currents are as short as possible. It is a good rule to position the circuit-breakers as shown in Figure 11. whenever possible. it is advisable that the main circuit-breaker is installed in the middle column or. as shown in Figure 12. however. Figure 12 Busbar 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards 2000 A 1200 A 3200 A 50 A Cables 100 A 300 A Advisable solution from a thermal point of view Figure 12a 500 A Busbar 3200 A 3200 A INCOMING FEEDER OUTGOING FEEDER Figure 11a NOT suggested positioning: The highest current (500 A) flows through the longest path Cables 500 A Heavier solution from a thermal point of view 300 A 100 A 50 A 50 A INCOMING FEEDER OUTGOING FEEDER ABB circuit-breakers inside LV switchboards 15 . particular attention shall be paid to prevent the obstruction of the ventilation openings in the fixed part of the circuit-breaker (Figure 14). To this purpose. IEC/TR 60890. the larger the exchange surface towards the outside and the better the exchange conditions depending on the installation modality are.. the greater amount of heat is released. As regards the positioning of the ventilation openings. bottom and side walls) and therefore. the other one shall be positioned at the top. which.���������������������������� 2. on the front part. is little impeded. For example. however. thus causing a reduction of the air “draught”.2 Dissipation of the heat generated inside switchboards After an analysis of the main heat sources and of the measures to limit heat generation. intended as the sum of the individual surface areas (top. Figure 13 2. this chapter shall take into consideration the switchboard ventilation.) “A0“ multiplied by the surface factor “b”. front.1 times the cross section of the inlets. as already said. It is important to remind that any openings at mid height could reduce the “draught chimney” effect.2 Side surfaces and positioning of switchboards It is necessary to take into account that a switchboard exchanges heat with the surrounding environment through its surfaces (top. As regards dimensioning. side. IEC/TR 60890 for temperaturerise assessment inside low voltage switchgear and controlgear assemblies prescribes for the enclosures with ventilation openings that the cross section for air outlets is 1.2. the switchboard should be positioned so that the air circulation around its external surface is facilitated or. The equipment inside the switchboard shall be positioned so that the circulation of the air is not excessively impeded by a reduction of the section for the air flow. the surfaces of the switchboard and their positioning. which gives formulas and tables where constructional characteristics and installation modalities are in relation with the temperature-rise at the same power loss.. it is important that a good circulation of air inside the switchboard is realized (see Figure 13) and maintained. on the rear part. thus improving heat exchange. but introduces the concept of effective cooling surface “Ae”. IEC/TR 60890.. that is the different capacity of dissipating heat according to 16 ABB circuit-breakers inside LV switchboards . at the same power dissipation level by the internal components. In particular. Figure 14 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards 2. suggests a method for the temperature-rise assessment inside switchboards. for example.2. Many of these considerations derive from the Std. these are to be located so that the “draught chimney” effect is achieved: an opening shall be positioned at the bottom of the switchboard. does not consider the real external geometric surface of the switchboard. the air inlet surface of the switchboard is not fully exploited. . This factor takes into account the heat dissipation of the individual surfaces according to the type of installation of the enclosure.1 Switchboard ventilation To increase the switchboard cooling. the modalities through which switchboards can dissipate the heat towards the outside are described now. or on the “roof” of the switchboard. When disregarding this prescription. the possible ventilation openings are to be properly dimensioned and positioned. In case of withdrawable circuit-breakers. the form of internal separation of the switchboard and the degree of protection of the switchboard. This requirement is due to the greater volume of hot air (going out of the switchboard) in comparison with the cold air (going into the switchboard). IEC 60529. The degree of protection of a switchboard affects its capacity of dissipating heat: the higher the degree of protection is. The phenomena affecting heat dissipation by the circuitbreaker terminals are mainly convection (through the air moving inside the switchboard) and conduction (through the bars connected to the terminals). the presence of localized heating phenomena limiting the maximum service current of the circuit is quite frequent. Table 15: For enclosures with ventilation openings and effective cooling surface >1.5 Not taken into account 2. the choice of high degrees of protection is not recommended when they are unnecessary. The values of the parameter “b” related to the different surface types are shown in Table 13. rear side of wall-mounted enclosures Side faces of central enclosures Floor surface Surface factor “b” 1. For further information about the different forms of separation reference shall be made to the content of the Annex B or to the prescriptions of Std.3 2. e. the less heat is dissipated by the switchboard. e. As evident. Tables 14 and 15 show the multiplying factor “d” which IEC/TR 60890 suggests to use under particular conditions to increase the temperature-rise of the air inside the switchboard as a function of the number of horizontal partitions in the column under examination.05 1.25m2 Number of horizontal partitions n 0 1 2 3 Factor d 1 1. Ae =∑ (A0 x b) Table 13 Type of installation Exposed top surface Covered top surface.3 Dissipation of the heat generated in the terminals After a study of the main power sources inside the switchboard and of the modalities through which switchboards can dissipate the generated heat. e.2.4 Degree of protection of switchboards The degree of protection IP shows the protection of the enclosure against access to hazardous parts.15 1. front. Separation is obtained by means of metallic or insulating barriers or partitions. In practice.10 1. an analysis of how the circuit-breaker current carrying capacity can be improved by reducing local heating phenomena near the terminals shall be carried out. tends to rise to the top.5 0. it should be kept in mind that a defined degree of protection may be reached through different modalities. For example.2. the protection against the vertical fall of drops of water (IPX1) can be realized by such modalities so as not to affect heat dissipation and so as to keep the “chimney effect” inside the switchboard. The circuit-breaker typology which is most suitable for this configuration is the version providing vertical rear terminals. rear and side walls Covered side faces.g. From the tables above. even with low average air temperatures inside the switchboard.7 0. 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards 2.4 0.9 0. Besides.1 Problems linked to convection As a general principle linked to the phenomenon of convection.3. The code IP is the identification system of the degrees of protection based on the prescriptions of the Std. it results how horizontal partitions can cause air temperature rises up to 30% (3 partitions without ventilation openings).25m2 Number of horizontal partitions n 0 1 2 3 Factor d 1 1.15 2. of built-in enclosures Exposed side faces. Therefore. these phenomena are to be related with the typology of terminals used and to the version (fixed. withdrawable or plug-in) of the circuit-breaker installed. the busbar arrangement should be such as to present the minimum cross-sectional area to the air flow and to be licked by the air flow on its maximum surface. therefore in a “comb-like” arrangement. thus affecting the temperature inside the switchboard itself. when heat dissipation has not been optimized.3 Forms of internal separation of switchboards With separation form it is meant the type of division provided for the different circuits inside the switchboard.05 1. based on the convective motion of the air which.g. Table 14: For enclosures without ventilation openings and effective cooling surface >1. To take into consideration this phenomenon.the surface positions and to their being either exposed or covered. while heating. IEC 60439-1. remarkable separation forms tend to limit air circulation inside the switchboard. ABB circuit-breakers inside LV switchboards 17 .g. against ingress of solid foreign objects and ingress of water. Yet. The use of these terminals allows a better heat dissipation since. Figure 15 Circuit-breaker with horizontal terminals and vertical main busbars Main busbars running horizontally along the switchboard and vertically arranged For example. in the case of E4 and E6 circuit-breakers. This concept is definitely more evident when making reference to Figure 15. to facilitate the connection between the vertical terminals and the vertical connection busbars. one of the main problems to be faced when using vertical terminals is their complicated connection to the main busbar system when this runs horizontally along the switchboard with the busbar section arranged vertically. Figure 16 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Vertical terminals for E4 and E6 CBs (detail referred to one pole) Connection busbars Emax E6 Detail of the horizontal connection busbar with air flow direction Circuit-breaker with horizontal terminals Connection bars to the main busbars Circuit-breaker with vertical terminals and vertical main busbars Main busbars running horizontally along the switchboard and vertically arranged Bars properly bent Top view Connection bars to the main busbars Connection busbars Detail of the vertical connection busbar with air flow direction Vertical terminals Bars properly bent Circuit-breaker with vertical terminals 18 ABB circuit-breakers inside LV switchboards . since both busbars and terminals are oriented according to two simple connection planes. compared with the horizontal ones.���������������������������� Here are some practical considerations regarding use and installation modalities of vertical rear terminals for Emax series circuit-breakers. it is possible to use bars suitably bent as shown in Figure 16. they oppose a smaller cross-section to the natural motion of the air and a greater surface to thermal exchange. This problem is not present with the same busbar system when the circuit-breaker terminals are horizontal. Air circulation. Terminal On the contrary. Terminal Busbars Connection busbars Lower connection with front terminals. Air circulation. the lower terminals shall not divert too much the air flow and prevent it from reaching the upper terminals causing the loss of the benefits of cooling by convection. when in the presence of different upper and lower terminals. near the upper terminals (vertical). the solutions to be adopted must not impede the circulation of air in the upper terminals. near the upper terminals (vertical) is impeded. For example. when in the presence of upper vertical terminals and lower terminals of different type or. however. the positioning of the busbars acquires a remarkable importance. is only partially reduced. It should be kept into consideration that. ABB circuit-breakers inside LV switchboards 19 .As further example. Figure 18 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Busbars Connection busbars Terminal Busbars Connection busbars Lower connection with rear horizontal terminals. Figure 17 shows two other pictures representing an hypothesis of solution for the connection of the vertical terminals to the vertical connection busbar system for Emax E3 circuit-breakers. Figure 17 as Figure 18 shows. Therefore it is advisable to separate and keep apart as much as possible the connection busbars (from the main busbars to the circuit-breaker terminals) so that the heating condition does not get worse. for the improvement of the heating condition of busbars and terminals. Generally speaking. the more the clearance between the busbars. the more heat they dissipate and that the upper middle terminal is usually that with the most problems from the thermal point of view. here is an example of the solutions which can be adopted. particular measures can be taken to improve the heat exchange of these terminals. due to their positions. with reference to the thermal exchange through the phenomenon of conduction. in the case of threepole circuit-breakers. their dimensioning and position shall have to take into account this double function. Therefore. with a solution as that shown in Figure 20. the connection busbars convey heat far from the terminals. Figure 22 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards In case of circuit-breaker connection through busbar systems with the three phases vertically arranged. as Figure 19 shows. reach the highest temperatures. for example by lengthening the horizontal part of the upper connection busbars in comparison with the lower ones. In particular. There is a rise in the heat exchanged by conduction both when the cross-section through which heat is exchanged enlarges (contact section between the cables or the connection busbars and the circuit-breaker terminals). the upper terminals and in particular the upper middle terminal are usually those which. or by treating busbars and dissipators with special paints.2 Problems linked to conduction Instead. as well as when the temperature difference between the bodies in touch involved by this exchange increases. the terminals of a circuitbreaker release heat also towards the busbars or the cables connected to them. as shown in Figure 21.���������������������������� For example. the external connections can be taken out of alignment with the terminals. without creating. besides carrying the current.3. a surface thermal insulation. on the other hand. Figure 21 Main busbars Top view 2. Figure 20 Main busbars Connection busbars As already mentioned. ABB SACE indicates the minimum cross-sectional area of the cables and busbars to be used. From this remark it results that. on their turn. Then. To obtain a connection allowing a sufficient heat exchange between the terminals and the distribution system of the switchboard. so that distance is increased. it is advisable that spacing of the 3 phases starts as near as possible to the circuit-breaker. the connection busbars shall effectively dissipate heat to keep their temperature low. which allow an increase in the radiated heat. Connection busbars 20 ABB circuit-breakers inside LV switchboards . Figure 19 Further increases in the carrying capacity of the circuits may be obtained by mounting some dissipators (see Figure 22) on the connection conductors – between the circuit-breaker and the busbar system – for a better heat dissipation. Table 16 Circuit-breaker type Tmax T2 T2-T4 T1-T2 T1-T2-T4 T1-T2-T4 T1-T2-T4 T1-T2-T4 T1-T2-T4 T1-T2-T3-T4 T1-T2-T3-T4 T1-T2-T3-T4 T1-T2-T3-T4 T1-T2-T3-T4 T3-T4 T3-T4 T4-T5 T5 T5 T5-T6 T6 T6-T7 T7 T7 In [A] <=8 10 16 20 25 32 40 50 63 80 100 125 160 200 250 320 400 500 630 800 1000 1250 1600 The cross-sectional areas of the cables and busbars reported in Tables 16 and 17 are those used to determine the rated current carrying capacity of the circuit-breakers in free air according to the Std.Here are the indications given for the molded-case circuit-breakers series Tmax and the air circuit-breakers series Emax. Cables [ n // ] x [ mm2 ] 1 1. IEC 60947-2.5 2. reported in Table 16 and in Table 17 respectively.5 2.5 4 6 10 10 16 25 35 50 70 95 120 185 240 2x150 2x185 2x240 3x240 4x240 5x240 20x5 25x5 40x5 50x5 2x30x5 2x40x5 2x50x5 2x60x5 2x80x5 2x100x5 Bars [ n // ] x [ mm x mm ] 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Table 17 Circuit-breaker Emax E1B/N 08 E1B/N 12 E2B/N 12 E2B/N 16 E2B/N 20 E2L 12 E2L 16 E3S/H 12 E3S/H 16 E3S/H 20 E3N/S/H 25 E3N/S/H 32 E3L20 E3L 25 E4H 32 E4S/H 40 E6V 32 E6V 40 E6H/V 50 E6H/V 63 Vertical terminals [ n // ] x [ mm x mm ] 1x(60x10) 1x(80x10) 1x(60x10) 2x(60x10) 3x(60x10) 1x(60x10) 2x(60x10) 1x(60x10) 1x(100x10) 2x(100x10) 2x(100x10) 3x(100x10) 2x(100x10) 2x(100x10) 3x(100x10) 4x(100x10) 3x(100x10) 4x(100x10) 6x(100x10) 7x(100x10) Front horizontal terminals [ n // ]x[ mm x mm ] 1x(60x10) 2x(60x8) 1x(60x10) 2x(60x10) 3x(60x10) 1x(60x10) 2x(60x10) 1x(60x10) 1x(100x10) 2x(100x10) 2x(100x10) 3x(100x10) 2x(100x10) 2x(100x10) 3x(100x10) 6x(60x10) 3x(100x10) 4x(100x10) 6x(100x10) ---------------------- ABB circuit-breakers inside LV switchboards 21 . 3. Figure 23 shows the curves reporting the carrying capacity of the Tmax molded-case circuit-breakers equipable with electronic relays. As regards the air circuit-breakers of Emax series. 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards T2 160 Fixed Note: in the plug-in version the maximum setting is derated by 10% F = Front flat terminals FC Cu = Front terminals for copper cables EF = Front extended terminals FC CuAl = Front terminals for CuAl cables ES = Front extended spread terminals R = Rear terminals T2 160 Plug-in F = Front flat terminals FC Cu = Front terminals for copper cables EF = Front extended terminals FC CuAl = Front terminals for CuAl cables ES = Front extended spread terminals R = Rear terminals Note: in the plug-in version the maximum setting is derated by 10% 22 ABB circuit-breakers inside LV switchboards . Table 19 reports the carrying capacity of the single apparatus at the different temperatures.���������������������������� 2.3 Current carrying capacity of circuit-breakers and busbars To conclude this chapter. whereas Table 18 reports the current carrying capacity of the Tmax molded-case circuit-breakers equipable with thermomagnetic releases. referred to the different temperatures and the different types of Figure 23 terminals and available versions. T4 250 Fixed Iu [A] 255 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards 250 245 240 VR 235 HR-F-FC 230 225 220 215 40 45 50 55 60 65 70 T [°C] FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals T4 250 Iu [A] Plug-in / Withdrawable 255 250 245 VR 240 235 230 225 220 215 210 205 40 45 50 55 60 65 70 T [°C] HR-F-FC FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals ABB circuit-breakers inside LV switchboards 23 . ���������������������������� T4 320 Fixed Iu [A] 330 320 310 300 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards VR 290 280 270 HR-F-FC 260 250 240 40 45 50 55 60 65 70 T [°C] FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals T4 320 Plug-in / Withdrawable Iu [A] 330 320 310 VR 300 290 FC-HR-F 280 270 260 250 240 30 35 40 45 50 55 60 65 70 T [°C] FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals 24 ABB circuit-breakers inside LV switchboards . T5 400 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Fixed Iu [A] 405 400 395 390 385 VR 380 HR-FC-F 375 370 365 360 355 350 40 45 50 55 60 65 70 T [°C] FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals T5 400 Plug-in / Withdrawable Iu [A] 405 400 395 390 385 380 375 370 365 360 355 350 345 340 335 330 35 40 45 50 55 60 65 70 T [°C] VR HR-FC-F FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals ABB circuit-breakers inside LV switchboards 25 . ���������������������������� T5 630 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Fixed Iu [A] 640 630 620 610 600 590 580 570 560 550 540 530 520 510 500 490 480 470 30 35 40 45 50 55 60 65 70 T [°C] VR HR-FC-F FC = Front terminals for cables VR = Rear flat vertical terminals F = Front flat terminals HR = Rear flat horizontal terminals T5 630 Iu [A] Plug-in / Withdrawable 600 550 VR 500 EF-HR 450 400 35 40 45 50 55 60 65 70 T [°C] EF = Front extended terminals HR = Rear flat horizontal terminals VR = Rear flat vertical terminals 26 ABB circuit-breakers inside LV switchboards . )terminals T6 630 Withdrawable 4 VR EF-HR EF = Front extended terminals HR = Rear flat horizontal terminals VR = Rear flat vertical terminals ABB circuit-breakers inside LV switchboards 27 .T6 630 Fixed 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards R(VR) F-FC R(HR) F = Front flat terminals FC = Front terminals for cables R(VR)=Rear(vertical)terminals R(HR) = Rear(horiz. ���������������������������� T6 800 Fixed R(VR) 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards F-FC R(HR) F = Front flat terminals FC = Front terminals for cables R(VR)=Rear(vertical)terminals R(HR) = Rear(horiz.)terminals T6 800 Withdrawable 4 VR EF-HR EF = Front extended terminals HR = Rear flat horizontal terminals VR = Rear flat vertical terminals 28 ABB circuit-breakers inside LV switchboards . T6 1000 1100 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Fixed 1000 R(VR) 900 FC ES R (HR) 35 40 45 50 55 60 65 70 FC = Front terminals for cables R (HR) = Rear flat horizontal terminals R (VR) = Rear flat vertical terminals ES = Front extended spread terminals ABB circuit-breakers inside LV switchboards 29 . T7 V 1000 Withdrawable 1050 1000 950 VR 900 EF-HR 35 40 45 50 55 60 65 70 EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals 30 ABB circuit-breakers inside LV switchboards .���������������������������� T7 V 1000 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Fixed 1050 1000 VR 950 900 EF-HR 35 40 45 50 55 60 65 70 EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals Note: For ratings below 1000 A Tmax T7 does not undergo any thermal derating. T7 S. 1250 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Fixed 1300 1250 1200 1150 1100 VR EF-HR 1050 1000 950 900 850 800 35 40 45 50 55 60 65 70 EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals T7 V 1250 Fixed 1300 1250 1200 1150 1100 1050 VR EF-HR 1000 950 900 850 800 35 40 45 50 55 60 65 70 EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals ABB circuit-breakers inside LV switchboards 31 .H.L. L. 1250 1300 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Withdrawable 1250 1200 1150 VR 1100 1050 1000 950 900 850 800 35 40 45 50 55 60 65 70 EF-HR EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals T7 V 1250 Withdrawable 1300 1250 1200 1150 1100 1050 1000 950 900 850 800 35 40 45 50 55 60 65 70 VR EF-HR EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals 32 ABB circuit-breakers inside LV switchboards .���������������������������� T7 S.H. L. 1600 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Fixed 1700 1600 1500 1400 VR EF-HR 1300 1200 1100 1000 35 40 45 50 55 60 65 70 EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals T7 S.H.T7 S.H. 1600 1700 Withdrawable 1600 1500 1400 VR 1300 1200 EF-HR 1100 1000 35 40 45 50 55 60 65 70 EF = Extended front terminals VR = Rear flat vertical terminals HR = Rear flat horizontal terminals ABB circuit-breakers inside LV switchboards 33 .L. 8 11 14 18 22 28 35 44 56 70 88 112 40 °C MAX 1.5 1.9 8.5 1.9 1.5 16 20 25 32 40 50 63 80 100 125 160 MIN 1 1.8 2.1 1.1 13 16 20 26 32 40 51 64 80 101 129 MAX 1.2 4 5.3 1. 34 ABB circuit-breakers inside LV switchboards .7 10.3 4.5 5.5 14.2 4 5 6.4 8 10.5 9.2 4 5. Tmax T3 10 °C In [A] 63 80 100 125 160 200 250 MIN 51 64 80 101 129 161 201 MAX 72 92 115 144 184 230 287 MIN 49 62 77 96 123 154 193 20 °C MAX 69 88 110 138 176 220 278 MIN 46 59 74 92 118 147 184 30 °C MAX 66 84 105 132 168 211 263 MIN 44 56 70 88 112 140 175 40 °C MAX 63 80 100 125 160 200 250 MIN 41 52 65 82 104 130 163 50 °C MAX 59 75 93 116 149 186 233 MIN 38 48 61 76 97 121 152 60 °C MAX 55 69 87 108 139 173 216 MIN 35 45 56 70 90 112 141 70 °C MAX 51 64 80 100 129 161 201 (*) For plug-in circuit-breakers.9 2.1 7.2 4 5 6.4 1.7 9.6 2 2.2 2.5 6.���������������������������� Table 18 Tmax T1 and T1 1P (*) 10 °C In [A] 16 20 25 32 40 50 63 80 100 125 160 MIN 13 16 20 26 32 40 51 64 81 101 129 MAX 18 23 29 37 46 58 72 92 115 144 184 MIN 12 15 19 25 31 39 49 62 77 96 123 20 °C MAX 18 22 28 35 44 55 69 88 110 138 176 MIN 12 15 18 24 29 37 46 59 74 92 118 30 °C MAX 17 21 26 34 42 53 66 84 105 131 168 MIN 11 14 18 22 28 35 44 56 70 88 112 40 °C MAX 16 20 25 32 40 50 63 80 100 125 160 MIN 11 13 16 21 26 33 41 53 66 82 105 50 °C MAX 15 19 23 30 38 47 59 75 94 117 150 MIN 10 12 15 20 25 31 39 49 61 77 98 60 °C MAX 14 18 22 28 35 44 55 70 88 109 140 MIN 9 11 14 18 23 28 36 46 57 71 91 70 °C MAX 13 16 20 26 33 41 51 65 81 102 130 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards (*) For T1 1P circuit-breakers (fitted with TMF themomagnetic trip unit) consider only the column corresponding to the maximum adjustament of the TMD trip units.2 17 21 26 34 42 53 66 84 105 132 168 MIN 1.9 4.7 7.4 2.4 3 3.3 8 10 12.6 10 12 15 19 24 30 38 49 61 76 97 60 °C MAX 1.9 3.7 2.5 16 20 25 32 40 50 63 80 100 125 160 MIN 1.5 3.1 13 16 20 26 32 40 51 65 81 101 129 (*) For plug-in circuit-breakers. Tmax T2 10 °C In [A] 1.2 9.8 3.6 7 8.7 5.5 8. a derating of 10% is to be considered.1 5.6 5.5 3.4 1.6 4.3 6.2 2.8 3.3 2.2 10 13 16 21 26 33 41 52 65 82 105 50 °C MAX 1.6 3.6 5.8 11 13.1 6.5 4.2 7.3 8 10 12.6 8.1 9 11 14 18 23 28 36 45 56 71 90 70 °C MAX 1.8 2.1 3.6 2 2.9 2.8 4.8 2.2 5.3 5.7 2.1 1.4 5.5 13.2 12 15 18 24 29 37 46 59 74 92 118 30 °C MAX 1.4 5.1 2.6 7.6 2 2.4 18 23 29 37 46 57 72 92 115 144 184 MIN 1.9 6.6 12 15 19 25 31 39 49 62 77 96 123 20 °C MAX 1.2 1.4 10.9 7.8 18 22 28 35 44 55 69 88 110 138 178 MIN 1.5 1.3 2.1 10.6 3.2 6.4 9.5 4.9 7.9 3.5 1.7 4.1 6.2 11.4 4.3 3 3.3 1.5 4.4 1.7 15 19 23 30 37 47 59 75 93 117 150 MIN 1 1.6 2.6 2 2.2 1.2 1.6 3.7 4.9 14 17 22 28 35 43 55 70 87 109 139 MIN 0.6 3.7 4. a derating of 10% is to be considered.1 2.9 6.3 1.5 3.2 2.8 2.8 3.5 7 8.5 8.3 11.8 3.8 2.9 2. Tmax T4 10 °C In [A] 20 32 50 80 100 125 160 200 250 MIN 19 26 37 59 83 103 130 162 200 MAX 27 43 62 98 118 145 185 230 285 MIN 18 24 35 55 80 100 124 155 193 20 °C MAX 24 39 58 92 113 140 176 220 275 MIN 16 22 33 52 74 94 118 147 183 30 °C MAX 23 36 54 86 106 134 168 210 262 MIN 14 19 30 48 70 88 112 140 175 40 °C MAX 20 32 50 80 100 125 160 200 250 MIN 12 16 27 44 66 80 106 133 168 50 °C MAX 17 27 46 74 95 115 150 190 240 MIN 10 14 25 40 59 73 100 122 160 60 °C MAX 15 24 42 66 85 105 104 175 230 MIN 8 11 22 32 49 63 90 107 150 70 °C MAX 13 21 39 58 75 95 130 160 220 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Tmax T5 10 °C In [A] 320 400 500 MIN 260 325 435 MAX 368 465 620 MIN 245 310 405 20 °C MAX 350 442 580 MIN 234 295 380 30 °C MAX 335 420 540 MIN 224 280 350 40 °C MAX 320 400 500 MIN 212 265 315 50 °C MAX 305 380 450 MIN 200 250 280 60 °C MAX 285 355 400 MIN 182 230 240 70 °C MAX 263 325 345 Tmax T6 10 °C In [A] 630 800 MIN 520 685 MAX 740 965 MIN 493 640 20 °C MAX 705 905 MIN 462 605 30 °C MAX 660 855 MIN 441 560 40 °C MAX 630 800 MIN 405 520 50 °C MAX 580 740 MIN 380 470 60 °C MAX 540 670 MIN 350 420 70 °C MAX 500 610 ABB circuit-breakers inside LV switchboards 35 . ���������������������������� Table 19 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards X1 withdrawable – rear horizontal terminals Temperature [°C] 10 20 30 40 45 50 55 60 X1 630 % 100 100 100 100 100 100 100 100 [A] 630 630 630 630 630 630 630 630 % 100 100 100 100 100 100 100 100 X1 1800 [A] 800 800 800 800 800 800 800 800 % 100 100 100 100 100 100 100 100 X1 1000 [A] 1000 1000 1000 1000 1000 1000 1000 1000 % 100 100 100 100 100 100 100 100 X1 1250 [A] 1250 1250 1250 1250 1250 1250 1250 1250 % 100 100 100 100 100 97 94 93 X1 1600 [A] 1600 1600 1600 1600 1600 1550 1500 1480 X1 withdrawable – rear vertical terminals Temperature [°C] 10 20 30 40 45 50 55 60 X1 630 % 100 100 100 100 100 100 100 100 [A] 630 630 630 630 630 630 630 630 % 100 100 100 100 100 100 100 100 X1 1800 [A] 800 800 800 800 800 800 800 800 % 100 100 100 100 100 100 100 100 X1 1000 [A] 1000 1000 1000 1000 1000 1000 1000 1000 % 100 100 100 100 100 100 100 100 X1 1250 [A] 1250 1250 1250 1250 1250 1250 1250 1250 % 100 100 100 100 100 100 98 95 X1 1600 [A] 1600 1600 1600 1600 1600 1600 1570 1520 SACE Emax E1 Temperature [°C] 10 20 30 40 45 50 55 60 65 70 E1 800 % 100 100 100 100 100 100 100 100 100 100 [A] 800 800 800 800 800 800 800 800 800 800 % 100 100 100 100 100 100 100 100 100 100 E1 1000 [A] 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 % 100 100 100 100 100 100 100 100 99 98 E1 1250 [A] 1250 1250 1250 1250 1250 1250 1250 1250 1240 1230 % 100 100 100 100 98 96 94 92 89 87 E1 1600 [A] 1600 1600 1600 1600 1570 1530 1500 1470 1430 1400 36 ABB circuit-breakers inside LV switchboards . 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards SACE Emax E2 Temperature [°C] 10 20 30 40 45 50 55 60 65 70 E2 800 % 100 100 100 100 100 100 100 100 100 100 [A] 800 800 800 800 800 800 800 800 800 800 % 100 100 100 100 100 100 100 100 100 100 E2 1000 [A] 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 % 100 100 100 100 100 100 100 100 100 100 E2 1250 [A] 1250 1250 1250 1250 1250 1250 1250 1250 1250 1250 % 100 100 100 100 100 100 100 98 96 94 E2 1600 [A] 1600 1600 1600 1600 1600 1600 1600 1570 1538 1510 % 100 100 100 100 100 97 94 91 88 85 E2 2000 [A] 2000 2000 2000 2000 2000 1945 1885 1825 1765 1705 SACE Emax E3 Temperature [°C] 10 20 30 40 45 50 55 60 65 70 E3 800 % 100 100 100 100 100 100 100 100 100 100 [A] 800 800 800 800 800 800 800 800 800 800 E3 1000 % 100 100 100 100 100 100 100 100 100 100 [A] 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 E3 1250 % 100 100 100 100 100 100 100 100 100 100 [A] 1250 1250 1250 1250 1250 1250 1250 1250 1250 1250 E3 1600 % 100 100 100 100 100 100 100 100 100 100 [A] 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 E3 2000 % 100 100 100 100 100 100 100 100 100 100 [A] 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 E3 2500 % 100 100 100 100 100 100 100 100 97 94 [A] 2500 2500 2500 2500 2500 2500 2500 2500 2425 2350 E3 3200 % 100 100 100 100 100 97 93 89 86 82 [A] 3200 3200 3200 3200 3200 3090 2975 2860 2745 2630 SACE Emax E4 Temperature [°C] 10 20 30 40 45 50 55 60 65 70 E4 3200 % 100 100 100 100 100 100 100 100 98 95 [A] 3200 3200 3200 3200 3200 3200 3200 3200 3120 3040 E4 4000 % 100 100 100 100 100 98 95 92 89 87 [A] 4000 4000 4000 4000 4000 3900 3790 3680 3570 3460 SACE Emax E6 Temperature [°C] 10 20 30 40 45 50 55 60 65 70 E6 3200 % 100 100 100 100 100 100 100 100 100 100 [A] 3200 3200 3200 3200 3200 3200 3200 3200 3200 3200 E6 4000 % 100 100 100 100 100 100 100 100 100 100 [A] 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 E6 5000 % 100 100 100 100 100 100 100 98 96 94 [A] 5000 5000 5000 5000 5000 5000 5000 4910 4815 4720 E6 6300 % 100 100 100 100 100 100 98 96 94 92 [A] 6300 6300 6300 6300 6300 6300 6190 6070 5850 5600 ABB circuit-breakers inside LV switchboards 37 . (*) minimum clearance between the central conductors: 50mm. In general. whereas for big-size molded-case circuitbreakers (starting from T4).4 for not painted bars and 0.���������������������������� As regards small-size molded-case circuit-breakers there is no remarkable difference among the various terminal typologies. passing from bare busbars to painted busbars there is an increase in the current carrying capacity which can reach also 15%. the behaviour of the rear horizontal terminals is analogous to that of the front ones. the fixed version is suggested instead of the withdrawable and the plug-in ones. Table 20 Width x Thickness [mm] x [mm] 50 x 5 50 x 10 60 x 5 60 x 10 80 x 5 80 x 10 100 x 5 100 x 10 I 583 852 688 985 885 1240 1080 1490 Carrying capacity in A a. the rear vertical terminals are to be preferred to the other terminal typologies when the circuit-breaker is installed in vertical position. to determine its current carrying capacity reference should be taken to the lowest curve in the graphics. DIN 43671 for copper conductors of rectangular cross-section in indoor installations. where the radiation coefficient is assumed to be equal to 0. In the same way. under the same conditions in the busbar system.c. 2 Advices to improve the current carrying capacity of the circuit-breakers inside switchboards Carrying capacity in A up to 60Hz for painted copper conductors I 679 1020 826 1180 1070 1500 1300 1810 II 1140 1720 1330 1960 1680 2410 2010 2850 III 1330 2320 1510 2610 1830 3170 2150 3720 II II* 2010 2950 2310 3290 2830 3930 3300 4530 1920 2600 2210 2900 2720 3450 3190 3980 Validity condition of the table: ambient temperature 35°C. up to 60Hz for bare copper conductors II 994 1510 1150 1720 1450 2110 1730 2480 III 1240 2040 1440 2300 1750 2790 2050 3260 II II* The greater heat dissipation capacity is definitely that of the rear vertical terminals. 38 ABB circuit-breakers inside LV switchboards . As it can be observed from the table. As regards the air circuit-breakers of Emax series. conductor width vertical. clearance between conductors in parallel equal to conductor thickness. Table 20 shows the different current carrying capacity given by the Std. as an example. conductor temperature 65°C. however.9 for painted bars. If the circuit-breaker were installed in horizontal position. 1 2. can withstand satisfactorily for the operating time of the device under the test conditions specified.5 0. related to the Icw by a coefficient “n”. 3.5 1.rated conditional short-circuit current.1 Main definitions of the parameters characterizing a switchboard under short-circuit conditions As far as the short-circuit withstand strength of a switchboard is concerned. an analysis shall be carried out to illustrate the prescriptions regarding the electrical circuits of switchboards and the modalities aimed at reducing the possibility of occurrence of a short-circuit on the circuits inside the switchboards and to reduce its effects. the circuit of a switchboard protected by a suitable device shall have a rated conditional shortcircuit current if it can withstand the electro-dynamic stresses due to the peak current limited by the protective device and a specific thermal energy let through by the protective device in correspondence with the prospective short-circuit current Ik. Rated peak withstand current “Ipk” The rated peak withstand current of a switchboard circuit is the value of peak current assigned to that circuit by the manufacturer which that circuit can withstand satisfactorily under the test conditions specified by the Standard. The peak current value. The information concerning the shortcircuit withstand strength of the switchboard are given by the manufacturer according to the presence or not of the protective device.2 3. After a short introduction defining the main electrical parameters related to short-circuit.s.2 n 1. which is used to determine electro-dynamic stresses. value of short-time current assigned to that circuit by the manufacturer which that circuit can carry without damage under the test conditions specified by the Standard. IEC 60439-1 about low voltage controlgear and switchgear define the above parameters as follows : Rated short-time withstand current “Icw” The rated short-time withstand current of a circuit of a switchboard is the r. making specific reference to the interaction between the protection circuit-breaker installed in the switchboard and the switchboard itself. Unless otherwise stated by the manufacturer. With reference to these definitions. stated by the manufacturer. ABB circuit-breakers inside LV switchboards 39 . To this short-time current a determined peak value “Ipk” is associated and it is assumed that the maximum current value which can occur and which can be withstand by the switchboard does not exceed the peak value. the main parameters characterizing a switchboard are: .rated short-time withstand current.3 0.1 General prescriptions and information about short-circuit withstand strength As regards the short-circuit withstand strength of an assembly. The values normalized by the multiplying factor “n” are reported in Table 21. The Std. the reference time is 1s. is obtained by multiplying the short-time current by the coefficient “n”.7 2 2. .1. protected by a short-circuit protective device specified by the manufacturer.m. can withstand the electro-dynamic stresses due to the initial peak value which can reach a maximum value equal to “Icw x n” and a specific thermal energy due to the current and equal to Icw2 x t (with t=1s).25 0.3 Problems concerning short-circuit In this chapter the problems regarding short-circuit are analyzed. .7 0. On the other hand. Table 21 Values normalized by coefficient “n” RMS value of short-circuit current kA I ≤ 5 5 < I ≤ 10 10 < I ≤ 20 20 < I ≤ 50 50 < I 3 Problems concerning short-circuit Coϕ 0. which that circuit. the Std. Rated conditional short-circuit current “Icc” The rated conditional short-circuit current characterizing the circuit of a switchboard is the value of prospective short-circuit current. it is possible to say that the circuit of a switchboard for which a specific Icw has been defined.rated peak withstand current. IEC 60439-1 prescribes that the user of the switchboard shall give the manufacturer the data relevant to the short-circuit currents at the installation point so that the assembly is protected against shortcircuit by protective devices – for example automatic circuit-breakers positioned inside or outside the switchboard – and so that it is manufactured to withstand the thermal and dynamic stresses occurring under shortcircuit conditions. .allowable short-time withstand current Icw.2. if the initial peak value is not specified. The switchboard of Figure 25 to be installed in a plant with a prospective short-circuit current Ik equal to 100kA at 400V is now taken as example.2 Prescriptions concerning the electrical circuits of a switchboard In addition to the previous general prescriptions concerning the indication of the short-circuit withstand strength of a switchboard. which shall be designed so that the likelihood of a short-circuit on the busbars is remote. when the protective device is a circuit-breaker having a high Icw value. breaking capacity. this is understood to be linked to the assigned conditional short-circuit withstand current through the factor “n”. the circuit-breaker protecting the main busbar system is an Emax E4H with Icw = 100kA. short-circuit stresses limited by the protective devices installed on the supply side of the busbars. If also the busbar system has an Icw value equal to 100kA or higher. Unless otherwise specified. If the duration of the current is not specified. specifying the characteristics of the external device which protects the switchboard (rated current. different prescriptions must be complied with if reference is made to a main busbar system rather than to circuits derived from the busbars. expressed as: .an allowable value of short-time withstand current (Icw). Here is an application example to illustrate this concept: Figure 24 Icw=100kA 3 Problems concerning short-circuit SACE 3. the current is understood to be equal to 1sec. if the limiting characteristics of the protective device upstream the busbar system are not remarkable (or if they are not known in advance). For assemblies where a protective circuit-breaker is not incorporated in the incoming unit. the manufacturer shall indicate the maximum allowable value of short-circuit current. limited current. Ik=100kA 3. the busbars shall be rated in accordance with the information concerning the shortcircuit withstand strength and designed to withstand the In the switchboard of Figure 24.a rated conditional short-circuit current (Icc). As regards busbar dimensioning in relation to the shortcircuit withstand strength. the manufacturer may indicate: . the busbar system shall be rated so that the Icw is higher than the shortcircuit current value at the installation point. A Tmax T6L1000 is chosen as incoming circuit-breaker. the busbar system may be dimensioned to withstand the stresses due to the limited peak current and to the specific let-through energy limited by the circuit-breaker.1 Main busbar systems The main busbars (bare or insulated) shall be arranged in such a manner that an internal short-circuit is not to be expected under normal operating conditions. 40 ABB circuit-breakers inside LV switchboards . On the other hand. if the device protecting the main busbar system is an automatic circuit-breaker with current limiting characteristics.rated conditional short-circuit current Icc. specific let-through energy). when the protective device is a circuit-breaker having remarkable current limiting characteristics. The main prescriptions are given with reference to the internal busbar system. the circuit formed by the circuit-breaker and by the busbar system shall be considered to have Icw = 100kA. . the Standard prescribes how the electrical circuits inside the assembly must be dimensioned in order to reduce the possibility that a fault occurs. In practice.���������������������������� For assemblies with an automatic circuit-breaker incorporated in the incoming unit. I2t = 2500MA2s) can withstand greater stresses than those ones generated on the load side of T6L circuit-breaker. Figure 25 Icw=50kA 3. downstream the incoming apparatus. provided that these conductors are arranged so that under normal operating conditions. the circuit formed by the busbars and by the circuit-breaker shall have Icc = 100kA and therefore it is suitable for the prospective short-circuit current of the plant. may be rated on the basis of the reduced short-circuit stresses occurring on the load side of the respective short-circuit device. Thus. Dimensioned according to the limiting characteristics of T3 circuit-breaker T3 250 T3 250 T3 250 For example. a peak current value and a specific let-through energy exceeding those measured on the load side of the circuitbreaker shall correspond. or to the performances of the main circuit-breaker. For a correct dimensioning of the vertical distribution busbar. Figure 26 Dimensioned according to the limiting characteristics of the main circuit-breaker 3 Problems concerning short-circuit M a i n b u s b a r T2 160 b u s b a r T7 T2 160 D i s t r i b u t i o n Ic=100kA Dimensioned according to the limiting characteristics of T2 circuit-breaker Dimensioned according either to the limiting characteristics of the biggest circuit-breaker among the outgoing circuitbreakers of the single units. From this busbar. Conductors Figure 26 represents a switchboard where the vertical distribution busbar. supplying the main circuitbreakers of the different outgoing feeders.limited peak current lower than 80kA The presence of a current limiting apparatus inside the switchboard allows a busbar system with an Icw value < 100kA (short-circuit current in the plant) to be installed on the load side of this apparatus. is derived from the main busbar. an internal short-circuit between phases and/or between phases and earth is only a remote possibility. also in the event of a fault on the load side of the circuit- ABB circuit-breakers inside LV switchboards 41 . a busbar system characterized by an Icw value equal to 50kA can withstand the following parameters: . To conclude: it is possible to install a busbar system with an Icw value equal to 50kA on the load side of the circuit-breaker type T6L.specific let-through energy 50kA x 50kA x 1s = 2500MA2s .1 = 105kA As a consequence it is quite easy to verify that the busbar system (Icw = 50kA. above all when there are many circuits derived by a single main busbar system.In correspondence with the Ik values. it is possible to consider the outgoing device having the lowest current limiting performances. Ipk = 105kA.peak current 50kA x 2. in this case. constituted by a bare bar of solid manufacture and provided with spacers. however.2 Distribution busbars and conductors derived by the main busbars Within a section of an assembly. different horizontally-arranged conductors (in cable) depart. Such conductors are preferably of solid rigid manufacture. to which. as well as the components included in these units. so that the possibility that a short-circuit occurs can be considered as remote. the following parameters are verified: . The economical and dimensional advantages which result from this prescription of the Standard are evident.specific let-through energy lower than 20MA2s . the conductors and the distribution busbars positioned between the main busbars and the supply side of functional units.2. Contact with sharp edges must be avoided. or conductors insulated with a very high mechanical strength material (FTFE insulation). with basic insulation. There must be no risk of mechanical damage. As known. for example cables complying with IEC 60245-3.g. This distinction is made complying with the Tables 8 and 9 of the Std. for which mutual contact or contact with conductive parts shall be avoided. the busbar shall undergo acceptable stresses. for example by use of spacers. cables complying with IEC 60227-3. These conductors may only be loaded such that an operating temperature of 70° C is not exceeded: . The term conductor is used for busbars when the current exceeds or is equal to 400A. IEC 60439-1 suggests a series of measures which depend on the conductor typology. Figure 27 shows some diagrams relevant to Tmax and Emax series circuit-breakers allowing to determine. inside the switchboards it is necessary that cables and busbars are fastened to the frame. the dynamic stresses on the conductors could affect also the circuit-breaker terminals causing damages. Dimensioning of the distribution busbar carried out according to the above corresponds to the Standard prescriptions. the usual procedure for many switchboard manufacturers is dimensioning distribution busbars making reference to the performances of the circuit-breaker on the incoming of the switchboard. In fact. or single-core conductors. . the distances which can be obtained by the diagrams shall not undergo any variations. the Std. L [mm] 3 Problems concerning short-circuit 3.3. On the contrary. whereas the distances referred to the use of busbars are not valid when using cables.3 Reduction of the possibility of shortcircuit events and of the relevant effects As regards the prescriptions aimed at making unlikely the occurrence of a short-circuit in live conductors.conductors with basic insulation (cables complying with IEC 60227-3). When specific requirements demand or prescribe the use of busbars also for currents lower than 400A.single-core conductors with basic insulation and a maximum permissible conductor-operating temperature above 90° C.���������������������������� breaker with lower limiting characteristics. the maximum distances from the circuit-breaker terminals to the first anchor element of the conductors. for which there are no additional requirements if there is no risk of mechanical damage. in spite of this. IEC 60439-1.1 Minimum anchor distances for conductors One of the main problems which regard short-circuit and which is to be faced directly by panel builders is the maximum anchor distances of the conductors connected to the circuit-breakers from the circuit-breaker terminals. for which mutual contact or contact with conductive parts is permitted where there is no applied external pressure. As an example here are the prescriptions intended for: . as a function of the maximum peak current under short-circuit conditions and of the circuit-breaker typology. 3. for example individual covered cables with shrink sleeving or individually run cables in plastic conduits. in terms of let-through energy and limited peak current value. the different cables which feed the individual circuit-breakers shall be dimensioned according to the limiting characteristics of the relevant device they supply. Tmax T1 350 300 250 200 150 100 50 0 10 Ipk [kA] 100 42 ABB circuit-breakers inside LV switchboards .bare conductors. or heating resistant PVC insulated cables according to IEC 60227-3. having additional secondary insulation. during a short-circuit. e. Figure 27 Distance suggested for the first anchor element of busbars as a function of the maximum prospective short-circuit current peak. whereas cables are referred to when the current is lower than this value. Circuit-breaker with horizontal and vertical terminals..front and rear terminals .connection by means of rigid busbars 600 3 Problems concerning short-circuit 500 L [mm] 400 200 150 100 200 50 0 10 L [mm] 100 Ipk [kA] 1000 300 100 Tmax T3 500 450 400 350 300 0 10 Ipk [kA] 100 1000 Distance suggested for the first anchor element of busbars as a function of the maximum prospective short-circuit current peak. L [mm] 250 200 150 100 50 0 10 100 1000 Emax 500 E1 B 450 E2 B-N E3 N-S-H 400 E4 S-H E6 H-V 350 Tmax T4 700 Ipk [kA] 300 600 L [mm] 250 500 200 400 E2 L L [mm] 150 300 E3 L 100 200 100 50 0 10 100 1000 0 Ipk [kA] 40 60 80 100 120 140 160 180 200 220 240 260 280 300 Ipk [kA] ABB circuit-breakers inside LV switchboards 43 .Tmax T2 450 400 350 300 250 Tmax T5 Valid for: . ���������������������������� As regards Tmax molded-case circuit-breakers. 50 200 200 50 Tmax T4 Tmax T5 Tmax T6 Tmax T7 2. Figure 28 gives an example of the maximum distance (in mm) suggested for the positioning of the nearest anchor supFigure 28 port.5÷10mm2 200 200 300 60 200 300 200 200 200 60 44 ABB circuit-breakers inside LV switchboards 200 3 Problems concerning short-circuit Tmax T1 Tmax T2 Tmax T3 16÷70mm2 1÷10mm2 200 50 200 50 200 . in relation to the maximum peak current admitted for the circuit-breaker. Table 22 Circuit-breaker Rated current In [A] ≤63 ≤63 ≤25 32-63 ≤125 ≤125 <160 160 ≤32 ≤50 ≤63 80 -160 63 80 100 125-160 200-250 20 32-50 80 100-320 320-1600 Rated voltage of the plant 3 Problems concerning short-circuit Emax X1 200 200 Emax E1÷E6 Vertical P Horizontal P 200 Type S200 S200M S200P S200P S800 S290 T1 T1 Front Flat 230Vac 20 25 40 25 50 25 50 37 120 120 120 120 37 27 21 18 16 200 200 200 200 10 415Vac 10 15 25 15 50 15 35 33 85 85 65 50 20 18 16 15 14 200 200 100 24 10 500Vac 15(In≤80A) 10(In≥80A) 15 15 50 39 30 29 18 17 15 14 13 150 150 48 21 10 690Vac 6(In≤80A) 4. In particular. the limiting characteristics of a circuit-breaker are a function of the working voltage of the circuit-breaker itself. .for the different protective circuitbreakers and the most common voltages of the plant – the values which approximately represent the maximum prospective short-circuit current in [kA] which guarantee a limited peak current not exceeding 17kA.2 Verification of the short-circuit withstand strength and of the current limiting characteristics of circuit-breakers In some cases. ABB circuit-breakers inside LV switchboards 45 .those protected by current limiting devices with a limited peak current not exceeding 17kA in correspondence with the maximum prospective short-circuit current measured at the terminals of the incoming circuit of the assembly. Figure 29 3. As known. as derived from the curves of Figure 28. the following switchgear and controlgear assemblies are free from verification: .those having rated short-time withstand currents or rated conditional short-circuit currents lower than 10kA. IEC 60439-1 allows that the shortcircuit withstand strength of assemblies is not verified. Figure 29 gives an example of the maximum distance (in mm) suggested for the positioning of the nearest anchor support for the busbars connecting to the circuit-breaker according to the different types of terminals available and for the highest peak values.5(In≥80A) 6 6 10 10 10 10 8 8 8 8 8 80 55 32 19 10 T2 T2 T2 T2 P P T3 T3 T3 T3 T3 T4 T4 T4 P Emax E1-E2 E3-E4-E6 E1-E6 Horizontal P [mm] 250 150 - P Vertical P [mm] 250 150 - Front P [mm] 250 Flat P [mm] 250 T4 T5 T6 T7 The short-circuit current value reported in the table above must be compared with the breaking capacity of the circuit-breaker for the different versions available.3. so that the short-circuit withstand test for the switchboard is not to be carried out.As regards Emax air circuit-breakers. Table 22 below gives . the Std. check that the connection busbars or cables do not reduce the air insulation distance Minimum centre distance for two circuit-breakers side by side Circuit-breaker width (mm) T1 T2 T3 T4 T5 T6 T7 3 poles 76 90 105 105 140 210 210 4 poles 102 120 140 140 184 280 280 Centre distance I [mm] 3 poles 76 90 105 105 140(*) 210 210 4 poles 102 120 140 140 184(*) 280 280 I (*) For Un ≥ 500 V minimum centre I (mm) 3 poles 180. for ABB SACE circuit-breakers series Tmax and Emax respectively.c. For 1000 V versions. Figure 30 Hereunder. please ask ABB SACE.3.���������������������������� 3.. Figures 30 and 31 give.3 Problems concerning the installation distances The Std. 46 ABB circuit-breakers inside LV switchboards . please ask ABB SACE. B Distances between two circuit-breakers side by side or superimposed For assembly side by side or superimposed. including the terminals. The dimensions to be respected must be added to the maximum dimensions of the various different versions of the circuit-breakers. such distances are already specified in the circuit-breaker technical catalogues and installation manuals. minimum centre I (mm) 4 poles 224 Minimum distance between two superimposed circuit-breakers H [mm] T1 T2 T3 T4 T5 T6 T7 60 90 140 160 160 180 180 Connection not insulated Cable terminal Insulated cable H H H Note: The dimensions shown apply for operating voltage Un up to 690 V. IEC 60439-1 assigns the circuit-breaker manufacturers the task of defining the prescriptions for the installation of these devices inside switchboards. 3 Problems concerning short-circuit Insulation distances for installation in metallic cubicle A [mm] 25 25 50 30(*) 30(*) 35(*) 50(*) B [mm] 20 20 25 25 25 25 20 C [mm] 20 20 20 25(*) 25(*) 20 10 A T1 T2 T3 T4 T5 T6 T7 C (*) For Un ≥ 440V and T6L all versions: distances A 100 mm Note: For the insulation distances of the 1000 V circuit-breakers. the indications relevant to the distances to be complied with in the plants up to 690 Va. please consider the same indications of Figure 30 referred to the insulation distance of Tmax T7 CB Emax – fixed version Emax – withdrawable version 500 500 A B 3 poles 4 poles 242 min. 282 max A B 3 poles 4 poles 380 ABB circuit-breakers inside LV switchboards 47 .Figure 31 3 Problems concerning short-circuit Compartment dimensions Emax E1 E2 E3 E4 E4f E6 E6f A [mm] 400 400 500 700 1000 B [mm] 490 490 630 790 880 1130 1260 Nota: For Emax X1 CB. whereas. shall be rated to withstand the conditioned current for 1 second and its relevant peak.5 100 The table above reports the data concerning the circuit-breakers installed in the switchboard and the relevant effective current carrying capacities obtained by the tests carried out in compliance with IEC 60439-1.400A Q3 Q8 S4L . which is provided with a non-current-limiting circuit-breaker.9 4500 100 220 Q2 E3H 2500 0. for the section A. which are equipped with a current limiting circuit-breaker.1250A S6L . the distribution busbar too shall be dimensioned as the main busbar.5 100 Q7 S6L 630 0.8 2000 100 220 Q3 E2L 1250 0.85 1062. First example Configuration of the switchboard front Section A Section B Section C S7L . for the section C.9 1125 100 Q5 S7L 1600 0.85 212.85 1360 100 Q6 S7L 1250 0.5000A E3 .85 535. If not. the current carrying capacities of the circuit-breakers inside the switchboard shall be very near to the rated ones.5 100 Q8 S5L 400 0. by positioning the apparatuses properly and with conductors and busbars rated in compliance with cross-sectional areas and minimum length prescribed by the Standard. on the other hand. From this table it results also how the main distribution circuit (orange trace).85 340 100 Q9 S4L 250 0. the circuit-breakers shall be rated to withstand the peak and specific energy let-through by E2L. Dimensioning carried out in compliance with this criterion is valid only if it can guarantee that the possibility that a fault occurs on the distribution busbar is null. From these results it is evident that.9 1125 100 Q4 E2L 1250 0. the distribution circuits (brown trace).1600A E6 .���������������������������� Annex A Example of electrical switchboards with ABB circuit-breakers Annex A This Annex contains considerations about two different typologies of switchboards with ABB circuit-breakers.1250A Q1 Q2 Q6 E2 .630A SACE Q7 S5L . if the switchboard has been designed according to a correct layout and with suitable forms of separation.2500A Q5 SACE SACE S7L .1250A Supply SACE Q9 Q4 Switchboard characteristics Switchboard dimensions Degree of protection IP3X Heigth: 2300 mm Form of separation 4B Width: 2900 mm Depth: 1100 mm Data table Circuit Circuit-breaker Rated current In [A] Rated diversity factor Test current [A] Rated short-time current Icw [kA] Rated peak current Ipk [kA] Rated conditional short-circuit current Icc [kA] Q1 E6H 5000 0. 48 ABB circuit-breakers inside LV switchboards . they shall be sized according to the peak and specific energy let-through by S7L.250A E2 . shall be dimensioned according to the conditioned short-circuit current: thus. The same remarks of the previous case are valid also for the verification of the busbar protection. S7 1250A withdraw. T5 630A E6H withdrawable 5000A Q4 Q5 withdraw. as it results from an analysis of the data reported in the table. Under these conditions. the effective current carrying capacities of the circuits inside the switchboard turn out to coincide with the rated carrying capacities of the circuit-breakers. T5 400A T4 fixed 250A Switchboard characteristics Switchboard dimensions Degree of protection IP30 Heigth: 2320 mm Form of separation 4 Width: 1800 mm Depth: 1240 mm Data table Circuit Circuit-breaker Rated current In [A] Rated diversity factor Test current [A] Rated short-time current Icw [kA] Rated peak current Ipk [kA] Rated conditional short-circuit current Icc [kA] Q1 E6H 5000 1 5000 100 220 Q2 S7H 1250 1 1250 100 Q3 T5H 630 1 630 100 Q4 T5H 400 1 400 100 Q5 T4H 250 1 250 100 The conductors and busbars used for the realization of the circuits of this switchboard are of bigger cross-sections than those suggested by the Standard.Second example Annex A Configuration of the switchboard front Section A Chimney Section B Chimney Q2 Q3 Q1 SACE withdraw. ABB circuit-breakers inside LV switchboards 49 . Separation of terminals for external conductors from the functional units. including distribution busbars 50 ABB circuit-breakers inside LV switchboards . The following are typical forms of separation by barriers or partitions: Form 1 No internal separation Form 2 Form 2a Separation of busbars from the functional Terminals for external conductors not separated from busbars units Form 2b Terminals for external conductors separated from busbars Form 3a Form 3 Separation of busbars from the functional units Terminals for external conductors not separated from busbars and separation of all functional units from one another. enclosed protected spaces or compartments Symbols d c a b Caption a Enclosure b Internal separation c Functional units including terminals for associated external conductors d Busbars. but in individual. but not from those of other functional units Form 3b Terminals for external conductors separated from busbars Form 4 Separation of busbars from all functional units and separation of all functional units from one another. protection against contact with hazardous live parts belonging to the adjacent functional units and protection against the passage of solid foreign bodies from one unit of the assembly to an adjacent one can be attained. separate. Separation of terminals for external conductors associated with a functional unit from those of any other functional unit and the busbars Form 4a Terminals for external conductors in the same compartment as the associated functional unit Form 4b Terminals for external conductors not in the same compartment as the associated functional unit.���������������������������� Annex B Forms of internal separation Annex B By dividing assemblies by means of barriers or partitions (metallic or non-metallic) into separate compartments or enclosed protected spaces. Type of assemblies / Type of environment Switchgear and controlgear assembly: enclosed switchboard Assemblies for outdoor installation Assemblies with protection by total insulation Installations in normal environments Live parts which are not be touched intentionally Live parts which are readily accessible (horizontal top) Installations in locations containing a bath tube or shower basin Zones 1 and 2 Zone 3 Zones 1–2–3 public baths where water jets are used for cleaning purposes Installations for swimming-pools Zone 0 Zone 1 Zone 2 for indoor locations Zone 2 for outdoor location Zone 2 where water jets are used for cleaning purposes Installations for rooms and cabins containing sauna heaters Assemblies for construction sites (ACS) Standards and sub-clause IEC 60439-1 sub-clause 2.2 Minimum degree of protection Not defined IPX3 IP2XC IEC 60364-4 sub-clause 412.1.3 IEC 60439-1 sub-clause 7. C. S. IEC 60529. in accordance with the Std.2 IEC 60364-7 sub-clause 702. The degree of protection prescribed for an apparatus against access to hazardous live parts and against ingress of solid foreign objects and liquids is indicated by the Code IP.2.3 IEC 60439-1 sub-clause 7.512...512.2 IEC 60364-7 sub-clause 702.2 IEC 60364-7 sub-clause 703.3. A brief description of the IP Code elements is given hereunder.2 IEC 60364-7 sub-clause 702.2. it shall be replaced by the letter “X” (“XX” if both numerals are omitted).1 IEC 60364-4 sub-clause 412. or letter X) Additional letter (optional) (letters A.2 IEC 60364-7 sub-clause 701. W): IP Against ingress of solid foreign objects Against ingress of water with harmful effects Against access to hazardous parts Supplementary information When a characteristic numeral is not required to be specified. or letter X) Second characteristic numeral (numerals 0 to 8.2.2 IEC 60364-7 sub-clause 701.4. M. the table below reports the minimum degrees of protection for a switchgear and controlgear assembly to be installed in the specified environments in compliance with the above mentioned Standards.2 IPXXB (IP2X) IPXXD (IP4X) IEC 60364-7 sub-clause 701.2. B.512. Code letters (International Protection) First characteristic numeral (numerals 0 to 6.512.3.2 IEC 60439-4 sub-clause 7.1 IPX8 IPX5 IPX2 IPX4 IPX5 IP24 IP44 ABB circuit-breakers inside LV switchboards 51 .512.512.Annex C Degrees of protection (IP code) Annex C As example. D): Supplementary letter (optional) (letters H. IEC 60529. For full details reference shall be made to the Std.512.2.512.2 IEC 60364-7 sub-clause 702.2 IPX4 IPX1 IPX5 IEC 60364-7 sub-clause 702.1.512. test current of the circuit “2”.. direct current a.. test current of the circuit “3”. alternating current Ib full load current PCB power loss of the circuit-breaker at Ib PnCB power loss of the circuit-breaker at InCB InCB rated current of the circuit-breaker PSB power loss of the busbar at Ib PnSB power loss of the busbar at InSB InSB busbar rated current LSB busbar length PTQ total power dissipated inside the switchboard AE effective cooling surface b surface factor A0 sum of the individual surface areas d temperature coefficient IP degree of protection Icw rated short-time current Ipk rated peak withstand current Icc rated conditional short-circuit current Ik prospective short-circuit current n peak factor Glossary 52 ABB circuit-breakers inside LV switchboards . TT absolute temperature [°C] TA air ambient temperature [°C] ΔT temperature-rise [K] LV low voltage PTTA partially type-tested low-voltage switchgear and controlgear assembly d.. etc.c.���������������������������� Glossary fn rated diversity factor Inc rated current of the circuit I2test.c. I3test. . p.395.Telefax: +39 035. An ABB Group Company L. ABB SACE S. 35 24123 Bergamo .Italy Tel.CAL .306-433 http://www.000 .111 .com 1SDC007103G0201 December ’06 Printed in Italy 4.395. the characteristics and dimensions specified in this document may only be considered binding after confirmation by ABB SACE.Due to possible developments of standards as well as of materials.A.V.: +39 035.abb. Breakers Via Baioni.