single phase PEN protection within three phase supplies

If you have a 3 phase supply then there is a far better way to detect loss of PEN than looking for L-N voltages being a bit wild and you should use that.

Consider 3 equal resistors (or capacitors) between the 3 phases in 'star'. The centre of that star is a pseudo-neutral voltage, and an alarm wired between that and the supply neutral set to trigger at say 12V is a far cleaner indicator of PEN faults - much like the reference earth electrode idea.  (if there is a truly horrific overload so own phase dips very low or vanishes altogether it may also trip but that is probably an acceptable false alarm.)

Mike.

Subject to a standard risk assessment, one might conclude that, whether single or three phase, on its own the arrangement is not as low as reasonably practicable. A further control measure is available on at least one charger where current flowing to earth via a human body on loss of neutral opens the protective conductor to the car at around 17mA.

If you want a diagram try this thread:  RE: Open PEN detection for 722.411.4.1 (iv)

As Mike says, the same problem is present on 1-phase installations fed from 3-phase public supply, the difference is that without access to the other phases it's much harder to find a better alternative.

   - Andy.

This is great thanks! 

I have been to look at a job today,  a shop with a three phase supply and an E7 three phase meter is going to split to create two shops and a flat. 

So I need to contact WPD to request three single phase supplies for the three new premises to be supplied from the existing three phase head, both shops really need to have E7 supplies for storage heaters, the flat has a gas supply, but I'm thinking it should have an EV charge point in its parking bay.

I can't see that this could be considered a three phase installation if the three single phase supplies are installed from the same head. 

Would there be any issues regards using open PEN protection for one or more EV charge points?

I'd imagine on the basis of each phase being separately metered then you have no option than to fit single phase PEN protection unless a 3phase landlords supply remains that could be utilised 

In a perfect world it would split into 3 small 3 phase supplies perhaps 40A/phase but herein the UK we seem unable to grasp the idea that to have 3 phases in a home is OK, so suppliers, metering companies and domestic sparks are all totally unable to deal with it (and charge for it) sensibly. So it will be 3 supplies of 100A single phase and  some sort of lost PEN detector for whoever blinks and needs a charge point first.

Mike.

Is each of the two shops have a couple of storage heaters and the flat has an EV charger and they are all run over night that could be around 32 amps per phase and they would be nearly balanced, but obviously that’s not going to happen in real life as the heaters won’t be used all through the year.

Also chances are suppliers tariff will be more varied than existing E7 tariffs, such as the Octopus Agile tariff.