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.

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.

Chris Pearson said:

but a pair of neighbours could each hang one on the same boundary wall.

If they agreed to do so? Often boundary walls are shared property ... Party Wall Act may also apply to work on or near a boundary wall.

We probably ought to start a breakaway thread on 'when earthing is not good for you' but the risk of lifting a large patch of terra-firma to an dangerous voltage, measured relative to some  electrode in the ground carrying no current, placed far far away, is often over imagined, at least for short rod-like structures. For the UK 'classic' 4ft long 5/8 dia copper plated steel rod found beside the doorsteps of terraced houses with TT, even if the rod is raised to the full 240V, while an amp or two flows into the mud, the surface voltage falls away to a safe level within a metre or so of the top of the rod.

Mike

mapj1 said:

the surface voltage falls away to a safe level within a metre or so of the top of the rod.

Certainly by 2.5 m for horizontal underground pipes ... 

But 411.3.1.1 is to help reduce hand-to-hand potentials between accessible metallic parts that are solidly bonded to different earth potentials, rather than hands-to-feet ?

Indeed, but the hands to feet current path is not so easily mitigated by fences, brickwork etc.  Hand to hand connections round a barrier need arms like Mr Tickle. (*)
This was really intended as follow-on comment  from;-

"Possibly a bigger risk is.. 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. "

The forum post-ordering algorithm strikes again.

Mike

(*) For those wondering what I'm wittering  on about he is a cartoon character with very long flexible arms, ideal for testing simultaneous contact situations.

Chris Pearson said:

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

It would have to be quite a substantial wall ... I've been looking at a relatively small HP (5kW output) and the spec sheet says is weighs in at over 100kg!

    - Andy.

Chris Pearson said:

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

It would have to be quite a substantial wall ... I've been looking at a relatively small HP (5kW output) and the spec sheet says is weighs in at over 100kg!

    - Andy.

Hmm. that's the weight of the complete compressor and every thing presumably to minimise the size of the indoor part-  the reverse is also done where most of the thing is indoors and outside is just a heat-exchanger  so mostly empty space with a thing like a large car radiator, and a fan.

But you could certainly imagine either type standing side by side on the front of a row of terraced houses either direct underneath or off to one side of the downstairs front window.

Accessible to all and sundry passing by then.

Mike.

Hmm. that's the weight of the complete compressor and every thing

Indeed - that's for a monobloc system (the most popular these days I gather as it avoids having to charge refrigerant lines on-site as is the case with 'split' systems). There's yet another variant that runs the "brine" circuit between indoor and outdoors, and as you say the outdoor unit it little more than a heat exchanger and fan (and a de-frost heater) but for some reason that's only available in a 3-phase version (and won't de-frost from the heating circuit )

   - Andy.