EV charging is this TT or not, and within 1 meter of metal building is it safe?

[ericmark]

I don't understand, if using a TT supply why does it need a PEN isolating system? The box is connected to a bus bar chamber so can't see how the enclosure is not connected to the PME earth, the building is metal, and has three independent supplies to the building, originally a set of start up units, likely built by the council, but has been all owned by one company well before the company I work for bought it, the cost of removing two of the supplies was silly, so seemed a better idea to use them, other than being given money for the charging point, the company has nothing to do with the charging point, they did not install it. That was done by the company who manages it.

But the two labels don't seem to match up, if a TT supply why does it need a PEN isolation system?

 

[JohnW2]

I don't understand, if using a TT supply why does it need a PEN isolating system? .... But the two labels don't seem to match up, if a TT supply why does it need a PEN isolation system?

I agree that it doesn't make sense - I would suspect that one of the labels (probably the one which mentions TT) is 'incorrect'.

Mind you, it's potentially a bit confusing since, even if one uses a TN-C-S earth and a "PEN isolation system", then one pressumably still needs an earth rod of some sort, since, as one would expect, the reg in question says:

(iii) Protection against electric shock is provided by a device which disconnects the charging point from the live conductors of the supply and from protective earth in accordance with Regulation 543.3.3.101(ii) within 5 s in the event of the voltage between the circuit protective conductor and Earth exceeding 70 V rms. The device shall not operate if the voltage exceeds 70 V rms for less than 4 s. The device shall provide isolation. Closing or resetting of the device shall be by manual means only. Equivalent functionality could be included within the charging equipment.

... and the only way it can know the potential between PEN and earth is >70V is presumably by having some sort of earth rod, isn't it?

Kind Regards, John

 

[chivers67]

The Earlier charging points seemed to always get fitted with an Earth Rod didn't they just in case the Neutral was lost?

Modern ones now have a cut off device should the neutral get disconnected.

 

[JohnW2]

The Earlier charging points seemed to always get fitted with an Earth Rod didn't they just in case the Neutral was lost? ... Modern ones now have a cut off device should the neutral get disconnected.

Yes but, as I said, the "cut out device" would only be able to detect with certainty that the neutral had been lost if there were also an earth rod (to provide a reference for true earth potential).

I suppose the device could detect a fall in L-N potential difference, but there would be no certainty that that was due to the PEN having been 'lost'.

Kind Regards, John

 

[ericmark]

Since a metal building with three independent supplies it seems very unlikely the earth would be lost, but from the fact the building is bolted to earth and there are three independent PEN's coming into the building, so in real terms no problem.

However the board with the notice on is connected to the bus bar chamber with a barrel nut, so seems highly unlikely it is not earthed to the bus bar chamber, and the supply leaves the board with a standard SWA gland.

I would think the notices refer to the charging pod, rather than the board they are stuck on, it seems the safety officer has the keys to reset the pod should it trip out, he is also an electrical engineer/electrician so highly unlikely he would have made an error, but it still seems odd to have the two notices on the same box.

 

[JohnW2]

Since a metal building with three independent supplies it seems very unlikely the earth would be lost, but from the fact the building is bolted to earth and there are three independent PEN's coming into the building, so in real terms no problem.

I wouldn't be so sure about that, since it obviously depends on the location of the PEN fault - it is very possible that a single upstream fault could cause the PEN to be 'lost' by all three of these 'adjacent' supplies isn't it?

I would think the notices refer to the charging pod, rather than the board they are stuck on .....

One would certainly think that in terms of the left-hand one of the notices you posted, since it refers to a "Pod point 'PEN Isolation System' ".

Kind Regards, John

 

[ericmark]

and the only way it can know the potential between PEN and earth is >70V is presumably by having some sort of earth rod, isn't it?

I think monitoring the three phases if any are not between 207 and 253 volt, it is reasonably sure the PEN has not been lost, not quite as cut and dried if only monitoring one phase, but with all three reasonably sure.

 

[JohnW2]

I think monitoring the three phases if any are not between 207 and 253 volt, it is reasonably sure the PEN has not been lost, not quite as cut and dried

That obviously only applies if it is a 3-phase supply (which I presume you're saying it is), but I think what you are suggesting is iffy, anyway. If 3-phase loads are balanced between the three phases, the between-phases voltages would all be 'correct' even if there were no neutral at all, wouldn't it?

if only monitoring one phase, but with all three reasonably sure.

As I said, with single-phase, unless one has an earth reference (rod), all one could look for is a reduction in L-N voltage, and that's far from being proof of a 'lost PEN'.

Kind Regards, John

 

[ericmark]

PME shall not be used unless, and the unless is 722.411.4.1 and we have 5 options. There are a load of u-tube videos where the manufacturers claim that the 207 - 253 volt limit with a three phase system works, but raises questions as to if this can be used with a single phase system.

This as with many others goes through the options. About 5 minutes in it shows how two phases are within limits, but one phase is 288 volts so it would trip with a three phase supply, but not with a single phase.

Around the 9 minute mark it looks at single phase, it seems indent 5 allows other methods, and it seems using a RCD which also trips earth as well as line and neutral seems to be their answer.

I am not sure this complies, as the voltage to earth will be over 70 volts, but Zappi seems to think it does, but in my works case it is a three phase supply, so no real problem with the 207 to 253 volt limit.

In real terms the major danger is the charge points are right outside a personal entrance and the cables often cause a trip hazard, when first installed it was not used much, but it is getting more and more use, and it is easy when carrying items not to see a lead so close to the entrance.