O-Pen Device on a 3 phase PME distribution network

Question

Hi All, 
 Please can someone advise on installing an O-pen device that complies with Reg 722.411.4.1 (iv) on a 3 phase installation as the wording in amendment 2 has changed with the words 'in a single phase installation' now been removed. 
 My understanding from the CoP 4 was that the potential issue was that this devise will detect most conditions that arise through a break in the PEN, but when installed on a supply from a 3 phase PME distribution network there are a small number of conditions in which the line to neutral voltage appears to be within the normal utilization voltage range but the voltage on the PME earthing system has risen above 70 V rms. 
 Does this therefor mean that BS 7671 now consider this to no longer be a potential risk or is the risk so small, they don't deem it requires any further precaution? Surely there is still a risk this device wont detect the break and operate as required?? 
 And going forward, can we then assume that installing an EVSE with integral O-Pen protection that complies with indent (iv) is now perfectly acceptable on a 3 phase PME distribution network? 
 Regards 
 Mark

AJJewsbury · Accepted Answer

Evaluating the risk is tricky. Many have commented that voltages tend to swing about wildly during an open PEN event, so if the o-pen device latches off once the supply has once gone out of bounds and needs a manual reset once everything is back to normal, it's likely to be a lot safer than one that reconnects as soon as the supply appears to be back within tolerances. Likewise some models have additional c.p.c. current monitoring and will trip if it exceeds 30mA, so again giving an additional layer of protection. Unfortunately these kind of details don't appear to be stipulated by BS 7671 (or the illusive equipment standard) - so it's a matter of seeing what each manufacturer offers. 
 From what I've seen, charge points with in-built open-pen detection are more expensive than ones without, so if you have a few there may come a point where one upstream 3-phase detector and cheaper charge-points works out cheaper. 
 It's always a difficult argument, if a risk is acceptable in one situation (because technicalities make better solutions impractical), why should the same risk not also be acceptable in another situation (even if lower risk, if more expensive, solutions are technically possible). It's always somewhere between doing the best we can vs enough is enough, and what level of risk is acceptable to society in general seems to be rapidly moving goal posts. I don't envy those who write the standards like BS 7671 in that kind of situation. For the rest of us, I guess if we comply with the letter of the current regs, we shouldn't have to loose too much sleep. 
 - Andy.

O-Pen Device on a 3 phase PME distribution network

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