SIMULTANEOUS CONTACT QUESTION - 2 x EV vehicles parked next to each other

Just looking at this discussion from a practical point of view with  a view to ADS.

The supply to the EV charge points will have RCD protection on their supply, probably also a built in RCD. They will also have open pen detection, which should mean that if there was a significant issue with earthing due to an open pen conductor they should shut down. The RCD protection means that there only needs to be 30mA flowing to earth for the RCD to trip, I am struggle to think of a scenario where there would be a situation where the earthing of the two properties is separated to such an extent that 30mA will not flow under fault conditions, especially with open pen detection in place.

I can see that where RCD protection is not included and much higher currents are required for ADS having a guaranteed common earth is sensibly required.

Another approach that could be considered is looking at Indra chargers, they have an operating mode where they measure the voltage difference between their main earth and a reference electrode, if this increases beyond 30V the charger shuts down.

Alan B said:

Just looking at this discussion from a practical point of view with  a view to ADS.

The supply to the EV charge points will have RCD protection on their supply, probably also a built in RCD. They will also have open pen detection, which should mean that if there was a significant issue with earthing due to an open pen conductor they should shut down. The RCD protection means that there only needs to be 30mA flowing to earth for the RCD to trip, I am struggle to think of a scenario where there would be a situation where the earthing of the two properties is separated to such an extent that 30mA will not flow under fault conditions, especially with open pen detection in place.

But Regulation 411.3.1.1 applies even where RCD protection is in place ... I'm not sure how this gets round the issue?

The problem with 2 separate earthing systems is the fact that something else connected to either earthing system might have, say, 5 s disconnection time for a distribution circuit fault, and this might be seen at the exposed-conductive-parts of the other earthing system?

The RCD protection means that there only needs to be 30mA flowing to earth for the RCD to trip, I am struggle to think of a scenario where there would be a situation where the earthing of the two properties is separated to such an extent that 30mA will not flow under fault conditions, especially with open pen detection in place.

There are several possibilities - the 30mA RCD protection typically only covers the final circuit (or possibly the charge point itself) - so earth faults upstream of the RCD (e.g. on submains or even in  DNO cables) will also cause a rise of potential on the earthing system, and may well take up to 5s to clear (for current BS 7671 installations, potentially longer for older ones, perhaps into minutes for some DNO faults). Even faults in neighbouring installations can drag a shared earthing system (e.g. via DNO facility or bonding of shared metallic pipework) to hazardous voltages for hazardous lengths of time.  Same reason we still need main bonding even when every final circuit has 30mA RCD additional protection.

   - Andy.

Yep, a couple of years ago I had +180v between an outside tap and earth in one rural property connected to a TNCS earth. Turned out to be a fault to structural steel in a barn on a nearby farm that was connected to the same tx but as a TT system. The farm had only one RCD at the intake which failed to trip. The 180v was the voltage drop across the DNO electrode. That particular fault was evident for months, with the TNCS householder getting shock sensations. The DNO investigated but washed their hands of it when they confirmed it wasn’t open pen. 
I am not sure if I have a handle on all possible risks with simultaneous contact between EVs on separate earthing systems, but it seems illogical to expect neighbour A to have an EV charge point while neighbour B can’t because of what might be a relatively low risk. 

Actually I thought we had discussed this before, and indeed we have

And we dd not really resolve it very well then either,.

Personally I still think as I thought then, that chargers will magically appear, the earthing question will not always be considered rigorously, so many installations may not meet the regs, and it will all work just fine most of the time, so it wont be strongly enforced.

Mike.

Actually I thought we had discussed this before, and indeed we have

And we dd not really resolve it very well then either,.

Personally I still think as I thought then, that chargers will magically appear, the earthing question will not always be considered rigorously, so many installations may not meet the regs, and it will all work just fine most of the time, so it wont be strongly enforced.

Mike.

mapj1 said:

Personally I still think as I thought then, that chargers will magically appear,

As with charging caravans on driveways, some people won't care (or won't know).

mapj1 said:

he earthing question will not always be considered rigorously,

That's not necessarily the case ... 'cross-pavement charging' is bringing this to the forefront of people's minds now.

mapj1 said:

so many installations may not meet the regs, and it will all work just fine most of the time, so it wont be strongly enforced.

Until the "it will never happen" happens (because we will have very large numbers of EVs on charge soon) and then the poor electricians who did the job could well be hauled over the coals for it, because they didn't conform to the standard. 

Until the "it will never happen" happens 

That is always  risk - see the 'never happens' broken neutral debate -  and I'd like to hope that most installers will think and act sensibly. I'm also well aware , that here in the European western world we enjoy a very high, but also relatively very expensive, standard of electrical professionalism, and there is a long way for things to descend before plugging something in actually becomes comparably dangerous to most other human activities. There are however many places where this is true... 

It may be that to accelerate the roll-out of energy efficiency and 'Green' technology generally,  without needing to dig up every lawn or footpath first, there is a need to lighten up in some areas, on what we consider acceptable standards to be . Consider if class 1 heat pumps appear outside houses near neighbours. (do they warrent OPEN-like cover too ?). Do we encourage more casual or even DIY installation ? We might need to if the water levels get too deep...

Actually the very existence of an OPEN device compared to a few years ago, is an example of that kind of re-think for the rules at the consumer end, and the widening of the grid rate of frequency slew tolerances is an example of similar (& sensible in my view) pragmatism at the generation end.

I realise this is a sidetrack from the original topic, but it is possible that during the life of the installation, the rules regarding who can do what with earthing could change quite a bit, based on what has already happened during the last 50 years or so. 

(A variation on rules are shaped by the requirements of society - not just society being shaped by its rules.)

Mike

mapj1 said:

Consider if class 1 heat pumps appear outside houses near neighbours. (do they warrent OPEN-like cover too ?)

And the rules on where you can site a heat pump have now been relaxed, so it's possible to have two houses' heat pumps within touching distance of each other.

Will we see O-pen protection on heat pumps soon??? And the same issues we are having with SC that we have with EV?

rules on where you can site a heat pump have now been relaxed, so it's possible to have two houses' heat pumps within touching distance of each other.

Although typically with a fence or hedge or boundary wall in between, lessening the changes of someone actually touching both simultaneously.

Possibly a bigger risk is of one heatpump (or outdoor light, or EV or ... ) being held a a potential significantly different from the surrounding ground itself - ether because the ground is better at being at "true earth" potential, or because the local ground potential is raised (by lead sheathed cables or bonded metallic pipework) via the influence of another earthing system. Ditto for adjacent metalwork (e.g. fencing or garden supports) that can bring local ground potential to hand height (bypassing any shoe insulation) within reach of the HP. ADS really isn't ideal outdoors.

   - Andy.

Will we see O-pen protection on heat pumps soon???

On EVs, HPs, outside lights, sockets that could be used for class I equipment outdoors.... Why not just put an open-pen device at the origin and cover the whole installation? It could even be built into smart meters - presumably the voltage monitoring is already there, along with the ability to disconnect and it could even tell the DNO what's happening in real time. They'd just need an extra contact or two to switch N and PE (or PEN).

That said, single phase open-PEN technology relying on L-N (or L-PE) voltage measurement isn't 100% reliable - it can be blind to certain broken PEN conditions where 3-phase distribution is used, and likely won't spot the offset reference situations, like the one lyledunn mentioned above, at all.

Plus you need to be careful of extraneous-conductive-parts or other c.p.c.s by-passing the PE contact of the open-PEN device - e.g. pipework or c.p.c.s of control wiring (or screens of comms cables) for a HP. 

   - Andy.

AJJewsbury said:

On EVs, HPs, outside lights, sockets that could be used for class I equipment outdoors.... Why not just put an open-pen device at the origin and cover the whole installation?

Because it's simply not practicable ... because ... you can't permit bonding (main or supplementary), or accidental contact of exposed-conductive-parts with extraneous-conductive-parts, downstream of an OPDD, otherwise it's not working as an OPDD.

It might be possible (as done with some EV charging installations) to put an OPDD in a feeder pillar, and use this to supply a number of EV charging points ... but you do have to be careful.

AJJewsbury said:

That said, single phase open-PEN technology relying on L-N (or L-PE) voltage measurement isn't 100% reliable - it can be blind to certain broken PEN conditions where 3-phase distribution is used, and likely won't spot the offset reference situations, like the one lyledunn mentioned above, at all.

Plus you need to be careful of extraneous-conductive-parts or other c.p.c.s by-passing the PE contact of the open-PEN device - e.g. pipework or c.p.c.s of control wiring (or screens of comms cables) for a HP. 

Agreed.

You might just make the supply less reliable overall !!!

Because it's simply not practicable .

In some situations, yes, I'd agree. But in a conventional new build- all services coming in in plastic pipes, probably not even a copper phone line these days and supply cables PVC jacketed, wouldn't the argument against be weaker? Fortuitous contact with local terra firma might be undesirable in theory, but would pose a much lower risk in practice once the metallic connection to the DNO's PEN is removed. There may be advantages to doing it at the meter as well - loads that would contribute to pulling the severed PEN up to a hazardous voltage in the first place would be removed (estates of new builds would likely be 100% new meters) and early/accurate DNO notification should reduce the duration of the fault - both reducing the risks overall.

You might just make the supply less reliable overall !!!

Sure, swings and roundabouts with all options. Spending money on fixing the DNO's networks to reduce the likelihood of broken PENs in the first place rather than expensive gadgets in tens of millions of installations might be a better option when considered at a national scale (neither offering a 100% guarantee of course).

   - Andy.

AJJewsbury said:

Although typically with a fence or hedge or boundary wall in between, lessening the changes of someone actually touching both simultaneously.

You would think so, but a pair of neighbours could each hang one on the same boundary wall.

As Mike keeps saying, there are theoretical risks, and there is reality.