Yes this is a risk - some discussion here: https://engx.theiet.org/f/wiring-and-regulations/28198/open-pen-detection-for-722-411-4-1-iv

Note that the 'in a single phase installation' condition didn't preclude its use with a 3-phase distribution network - since most single phase installations are fed from 3-phase public networks. If you had a 3-phase installation it's possible to do a much more thorough job by creating an artificial neutral to compare voltage with. Of course that's not an option with single phase installations, and I guess not particularly practical if you happen to be on the end of a single phase submain on a larger site that has a 3-phase incomer either.

   - Andy.

HI Andy,

Thank you as always for your reply.

I did stumble across the attached thread after posting.

We install a number of chargers within the commercial and industrial sectors where obviously almost all sites are 3-phase, a number of which with private transformers & TN-S supplies so not an issue there.

Previously where installing on a TN-C-S, we would install a 3-phase O-pen device upstream the chargers, then a number of single phase supplies to the chargers.

We now have an option of installing chargers which have the integral built in O-Pen described in Indent (iv) but have still been allowing for the 3 phase O-Pen upstream as we believed there is still a risk. 

I suppose the question is are we been over cautious and increasing cost unnecessarily or is this the approach that you believe should be adopted unless confirmation is received from the manufacturer that the upstream O-pen is not required?

Regards 

Mark

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.