722.411.4.1 installing sp evcp with LOP on a 3ph&n supply tncs

Question

Installing single phase ev charger on a sp db fed from a 3phase&n supply origin 722.411.4.1 indent (i) was deleted after blue regs book to brown book, , also indent (iv)&(v) added along with (iii) in brown current regs book, amd2 so am I correct in thinking this is OK to install now with built in lop o-pen on a tncs tp&n supply,

gkenyon · Answer

AJJewsbury said: it is possible, under certain conditions, for c.p.c to be at a hazardous voltage but the L-N voltage still to be within normal range. 
 Whilst what Andy said here is true, it's not a statement that can easily be demonstrated to be low or high probability of serious electric shock in given circumstances, and is certainly not the whole picture. 
 This seemingly simple statement ignores the fact that rarely in three-phase systems is the phase balance maintained for long periods. In a real broken neutral situation, the line to neutral voltages on all phases constantly change. So if the broken PEN conductor is initially undetected, that situation will not persist continuously. If you have EV charging loads with the single-phase voltage monitoring open-PEN devices on all 3 phases, it is highly improbable that devices on all 3 phases will be "blinded" at the same time; in fact, the conditions are such that it's highly likely devices on two other phases will operate. This will change the phase balance very quickly, making it extremely likely that the remaining phase, on which OPDDs were originally "blinded" now see an "out of range" voltage in a relatively short time after the event. 
 In a similar way, the operating characteristic of 30 mA RCDs is not guaranteed to protect children ... that doesn't mean we can't use them and they are useless - they offer more protection than not having the RCD., but they wont' protect 100 % of people 100 % of the time.

722.411.4.1 installing sp evcp with LOP on a 3ph&n supply tncs

Join us to get the best from IET EngX.

Community Rules & Guidelines