Simultaenous Contact

Dom said:

I belive the nearest exposed conductive part, so yes it would be the car.

Of course that is the safe and sensible approach, but once the EVCP has been put in, the situation is out of the control of the installer. One householder might park a Nissan Micra (length < 4 m) tight up against the house; the next owner might have a motorhome which is twice as long.

BS 7671 won't let you just bond two separate earthing systems together, see Regulation 542.1.3.3.

It doesn't quite say you can't - rather applies conditions. In reality it's probably very common - bonding to shared water and gas mains (where they're still metallic) almost certainly crosses sub-station boundaries in many places - with very few apparent problems. It might be reasonable to conclude that complying with table 54.8 (for the larger of the two supplies) would be sufficient for the interconnecting bonding conductor. (Whether the 6mm² in the lamp-post would be sufficient is perhaps a problem for the owner of the lamp-post, and there's always the possibility they would object or refuse permission for such a connection to their equipment, which might make the approach untenable anyway, but at least the principle is there.)

The problem is that the departure undermines a basic premise of BS 7671, and also introduces risks that BS 7671 (and OPDDs) are not designed to handle. I'm not sure, therefore, it's a logical step to say 'no less safe' as required by Regulation 120.3.

BS 7671's stance isn't entirely consistent though - a Class 1 outdoor light within 2.5m of next door's gas pipe wouldn't trouble the words of 411.3.1.1 as the gas pipe is clearly an extraneous-conductive-part rather than an exposed-conductive-part - yet next door's gas pipe is very likely bonded to their earthing system which could be entirely separate to yours. Likewise there's no consideration of any other random bits of metalwork that could be stuck into the ground within reach of the light (handrails, fences etc. etc.) which too could have hazardous potential differences from your Earthing system. It might be an EV is riskier than an outside light (people grab hold of cars more often), but that's hardly a consideration for a general principle that 411.3.1.1 is meant to be dealing with.

I wonder if a testing could shed a plausible light on the earthing arrangements - testing between some accessible point on the lampost and the EVSE installation's MET - a significant voltage difference (without a significant load in the house) might suggest different earthing systems - and if that didn't suggest a problem a low-Ohms test might give an idea of the length of cable between the two (perhaps on the basis of 25mm² is around 0.727mΩ/m and 16mm² is around 1.15mΩ/m) if that approximately fits the likely cable lengths from house & post into the street, it seems unlikely they'd be on different systems. (Take readings both ways around, in case any standing voltages skew the results).

   - Andy.

Dom said:

I do feel there may be a case to look at this in terms of the additional 250mm-500mm hand held point however I also see the importance of the worst case sceanrio.

Since these are part of the fundamental requirements of BS 7671 and HD/IEC 60364-4-41, that will need to be proposed for work at international level, and agreed there, as well as in the UK.

It is also worth noting that the principle of "arms' reach" and the values associated with it (1.25 m for 1 arm, 2.5 m for two arms or arm above head of someone standing), are not new either ... they were illustrated in Figure 1 of the 15th Edition of the IEE Wiring Regulations in 1981:

The requirement in broadly its current form for simultaneously-accessible exposed-conductive-parts to be connected to the same earthing system where ADS is used has been in place since the 16th Edition of the IEE  Wiring Regulations was published in 1991 (Regulation 413-02-03).

These things may be inconvenient for this discussion, but we need to be careful not to throw the baby out with the bathwater. They are key principles that have been in place for a substantial length of time - at least 35 years now.

Dom said:

Where we have a tethered charge point of say 5 metres, would it be deemed safe to say that if we add the distance of charger lead, the EV car (max UK size) and then the 2.5 metre distance that this would be sufficient precaution?

What is the maximum length of a UK car? You certainly can't go off the standard UK parking space size of 4.5 m, as many SUVs exceed that length.

I believe (but you'd have to check) that a car can be up to 12 m long in theory.

And do we need to consider the trailer/caravan, especially if it is plugged into the car and so the chassis of the trailer or caravan is at the same potential as the vehicle body? I believe the total length then increases to 18.75 m for some vehicles?

However, many large vans and similar are also present on private driveways.

Finally, if the charging point is being installed according to Part S of the Building Regulations, or the particular provisions of the Scottish Technical Handbooks, tethered charging equipment doesn't appear to be permitted.

AJJewsbury said:

In reality it's probably very common - bonding to shared water and gas mains (where they're still metallic) almost certainly crosses sub-station boundaries in many places - with very few apparent problems. It might be reasonable to conclude that complying with table 54.8 (for the larger of the two supplies) would be sufficient for the interconnecting bonding conductor.

Bonding something that goes back into the ground for some distance, like common pipework, is not the same as simply linking the earthing arrangement of two electrical installations. Shared metallic pipework improves earthing performance.

Linking two installations without shared extraneous-conductive-parts is something very different!

AJJewsbury said:

wonder if a testing could shed a plausible light on the earthing arrangements

I'd be very careful with that ... even a CAT IV test instrument might struggle with HV faults, if you were to be unlucky enough to be conducting the test during one!

Linking two installations without shared extraneous-conductive-parts is something very different!

I'm not sure how much contact with terra firma could be relied upon to reduce currents flowing between the two earthing systems - in any case a 5" diameter steel pole sunk half a metre into the ground may well provide something of a true earth connection.

even a CAT IV test instrument might struggle with HV faults, if you were to be unlucky enough to be conducting the test during one!

If there's a HV fault in progress you're probably on dodgy ground just touching the lighting column at all. Presumably a similar risk overall to loop testing on a TT system? (where the local Earth wouldn't be pulled up by the HV faut even though the live conductors would).

   - Andy.

AJJewsbury said:

I'm not sure how much contact with terra firma could be relied upon to reduce currents flowing between the two earthing systems

More importantly, it helps with touch-voltages.

AJJewsbury said:

in any case a 5" diameter steel pole sunk half a metre into the ground may well provide something of a true earth connection

Not necessarily, and we have to discard the first 450 mm due to the effects of frost and drying out.

Thank you Graham,  

Dom said:

I have reviewed the requirements under Part S and the Scottish Technical Handbooks previously, and I cannot find any explicit prohibition on the use of tethered EV charge points.

Here is the requirement for untethered charging points in black and white in the SBSTH Domestic (April 2026):

And the non-domestic of April 2026:

Whilst there is no 'prohibition' there is a clear requirement for it to be untethered in Scotland.

And in AD-S:

There is a clear requirement for untethered, with the option for tethered only in exceptional circumstances (e.g. self-build and where the vehicle requirements are already known - since people change their vehicles, or have more than one, I'm not sure how "firm" one could be about the exception).

BUT ... this is only for charging points provided specifically where required by Part S or the Scottish Technical Handbooks ... if you are providing one when it's not required by Part S or the handbooks, or for general public use, that's another question.

This is all covered in the 5th Ed of the IET Code of Practice for Electric Vehicle Charging Equipment Installation.

gkenyon said:

I believe (but you'd have to check) that a car can be up to 12 m long in theory.

And do we need to consider the trailer/caravan, especially if it is plugged into the car and so the chassis of the trailer or caravan is at the same potential as the vehicle body? I believe the total length then increases to 18.75 m for some vehicles?

Not sure about that. Even an extended Rolls-Royce Phantom is just under 6 m, but the space to park it in is likely to be more than average. I suppose that there are stretched limos, but they may be too heavy for an ordinary car driving licence, and unlikely to be parked in front of an average semi.

That's why I suggested a motorhome earlier.