Circuit Breaker Selection was affected by Seventeenth Edition Amendment from the First of July 2015

Transcription

1 Circuit Breaker Selection was affected by Seventeenth Edition Amendment from the First of July 2015 Abstract A new compensation factor, Cmin, has been included in the UK regulation for protection from electric shock. It is intended to ensure that circuits supplied by slightly lower voltages than normal will provide protection from electric shock. This takes account of the fact that the voltage of the electricity supply to an electrical installation varies depending on time and place, changing of transformer taps and other considerations. Eddie Donnelly Tim Campbell November, 2015

2 Contents Protection Against Electric Shock, Regulation Calculation of Maximum Allowable Earth Loop Impedance According to Requirements for Electrical Installations IET Wiring Regulations Seventeenth Edition. BS7671: Common reasons a design may not meet this requirement... 3 Solutions Offered by Terasaki... 4 Appendix 1: Circuit Breakers with Integral Residual Protection Appendix 2: Maximum Allowable Earth Loop Impedance Values for TemBreak 2 Lite Range, in accordance with BS 7671:2008+A3:2015 Appendix 3: Maximum Allowable Earth Loop Impedance Values for TemBreak 2 Lite Range, in accordance with BS 7671:2008+A3:2015 Ref. Number: 15-MARK.UK.11 2

3 Protection Against Electric Shock, Regulation The impedance of the protective circuit should be low enough that it allows sufficient fault current to cause the circuit breaker to trip. The regulation is intended to ensure that a protective device will trip within 0.4 seconds if fault current flows in the protective conductor. Calculation of Maximum Allowable Earth Loop Impedance According to Requirements for Electrical Installations IET Wiring Regulations Seventeenth Edition. BS7671:2008 Before Amendment 3: 2015 Zs * Ia Uo Where Zs is the earth fault loop impedance in ohms Ia is the current in amperes causing operation of the protective device within the time specified in table 41.1 of regulation Uo is the nominal a.c. r.m.s. line voltage to earth in volts After Amendment 3: 2015, effective 1 st July 2015 Zs * Ia Uo * Cmin Where Zs is the earth fault loop impedance in ohms Ia is the current in amperes causing operation of the protective device within the time specified in table 41.1 of regulation Uo is the nominal a.c. r.m.s. line voltage to earth in volts Cmin is the minimum voltage factor to take account of voltage variations depending on time and place, changing of transformer taps and other considerations. Common reasons a design may not meet this requirement Common reasons a design may not meet this requirement are: Protective conductors are too small and present a large impedance to the fault current Protective device instantaneous trip thresholds are too high Ref. Number: 15-MARK.UK.11 3

4 Solutions Offered by Terasaki The most common solutions are: Reduce the value of current, which will operate the protective device in 0.4 seconds either by selecting a different device or by making an adjustment to its settings. All Terasaki TemBreak 2 MCCBs, including thermal magnetic types and electronic types, have adjustable instantaneous trip thresholds. This makes it easy to comply with Regulation by changing the setting, not the device. MCCB with adjustable Thermal and Adjustable Magnetic Characteristics Include RCD protection set at no greater than 30mA in the circuit Terasaki offer a wide range of DIN modular RCDs and RCBOs. In addition we have the only CBR (circuit breaker with integral residual current protection) based on an MCCB in the UK market. Refer to Appendix 1 for details of our CBR solution. Terasaki CBR Ref. Number: 15-MARK.UK.11 4

5 Lower the earth-fault loop impedance by increasing the cross-sectional area of the protective conductor We have re-calculated the maximum allowable earthfault loop impedance for each of our Moulded Case Circuit Breakers at maximum and minimum settings taking the new Cmin factor into account. The results are presented in Appendixes 2 and 3. Maximum allowable earth-fault loop impedance for Miniature Circuit Breakers (MCBs) are published in Table 41.3 of the Wiring Regulations. Ref. Number: 15-MARK.UK.11 5

6 Appendix 1: Circuit Breakers with Integral Residual Protection

7 Appendix 2 Maximum Allowable Earth Loop Impedance Values for TemBreak 2 Lite Range, in accordance with BS 7671:2008+A3:2015 MCCB REFERENCE S/C Protection Zs 230 Volts Setting In 0.4sec 5 sec 160AF 1P FIXED MAGS E160-SF, 25 ka AF THERMAL MAGNETIC FIXED E160-SF, 16 ka S160-SCF, 25 ka S160-SF, 40 ka AF THERMAL MAGNETIC MIN ADJUSTABLE MAX MIN E160-SJ, 16 ka MAX MIN S160-SCJ, 25 ka MAX MIN S160-SJ, 40 ka MAX MIN MAX MIN MAX MIN MAX

8 250AF THERMAL MAGNETIC FIXED E250-SCF, 16 ka E250-SF, 25 ka S250-SF, 40 ka 250AF THERMAL MAGNETIC MIN ADJUSTABLE MAX MIN E250-SCJ, 16 ka MAX MIN E250-SJ, 25 ka MAX MIN S160-SJ, 40 ka MAX MIN MAX

9 Appendix 3 Maximum Allowable Earth Loop Impedance Values for TemBreak 2 Range, in accordance with BS 7671:2008+A3:2015 MCCB REFERENCE S/C Protection Zs 230 Volts Setting In 0.4sec 5 sec S125NJ, 36kA MIN S125GJ, 65kA MAX MIN MAX MIN MAX MIN MAX MIN MAX MIN MAX S160NJ, 36kA MIN S160GJ, 65kA MAX MIN MAX MIN MAX MIN MAX MIN MAX MIN MAX MIN MAX H160NJ, 125kA MIN L160NJ, 200kA MAX S250NJ, 36kA MIN S250GJ, 65kA MAX MIN MAX MIN MAX

10 S250NE, 36kA S250GE, 65kA MIN S250PE, 70kA H250NE, 125kA MAX MIN MAX MIN MAX H250NJ, 125 ka MIN L250NJ, 200 ka MAX MIN MAX E400NJ, 25 ka S400CJ, 36 ka MIN S400NJ, 50 ka S400GJ, 70 ka MAX MIN MAX S400NE, 50 ka S400GE, 70 ka MIN H400NE, 125 ka L400NE, 200 ka MAX MIN MAX E630NE, 36 ka S630CE, 50 ka MIN S630GE, 70 ka MAX S800CJ, 36kA S800NJ, 50kA MIN S800RJ, 70kA MAX MIN MAX S800NE, 50kA S800RE, 70kA MIN MAX MIN MAX S1000SE, 50kA S1000NE, 70kA MIN MAX S1250SE, 50kA S1250NE, 70kA MIN S1250GE, 85kA MAX S1600SE, 50Ka S1600NE, 85kA MIN MAX

11 Ref. Number: 15-MARK.UK.11 Copyright Terasaki Electric (Europe) ltd. 2015