Motorhome or Caravan on EHU at Home

hitchglitch replied on 11/01/2019 10:47

Posted on 11/01/2019 10:47

This is a question for any practicing electricians on the forum, with apologies to other readers as it is a bit technical. Having just bought an electric vehicle and about to have a charger installed I have been researching some of the issues with houses on PME systems i.e. TN-C-S. An electric vehicle is a Class 1 appliance and has to be earthed so for an external charger installation I understand that an earth rod may be required to be connected to the charger.

So, as I have an extension lead from my garage to charge the motorhome on my driveway and my house is TN-C-S  (very common nowadays) with the vehicle outside the equipotential bonding area, there is a possible risk that the van’s metal work will be raised above earth potential (due to an open circuit neutral somewhere on the supply distribution) so creating the possibility of a potential difference between the van and the “true earth”. This is a safety risk.

Although I am qualified I am not up to date or practicing and do not want to pay hundreds of pounds to purchase the 18th Edition of the Regs and codes of practice but I am aware that PME is not allowed on caravan sites due to the problem outlined above. My question is, do the Regulations cover the situation that I have described above and, if so, what is the solution?

All informed comments welcomed.

brue replied on 11/01/2019 11:14

Posted on 11/01/2019 11:14

I asked OH as we do the same, motorhome linked to garage plus charger point. We are on a different system but you are apparently right about the potential need for a rod, an electrician would advise further (we check out with someone we know locally.)

hitchglitch replied on 11/01/2019 17:27

Posted on 11/01/2019 17:27

Sorry about that but what it means in practice is that if your house has a wiring system like many, many, others you maybe shouldn’t plug your motorhome or caravan in at home. Sounds daft? Well, that’s why I’m asking.

Of course, you can do what you like in your own home but it is good to know what the Regulations say and the Codes of Practice and what the risks are.

For electric cars charged in the driveway of your house the whole situation is a can of worms and I can’t see how vans are any different but hope somebody will point out the error of my ways.

derekcyril replied on 11/01/2019 19:29

Posted on 11/01/2019 19:29

Surely ,plugging in motorhome / caravan outside house is same as using club sites ? give me a clue what TN~C~S means cheers ,derek

hitchglitch replied on 11/01/2019 21:57

Posted on 11/01/2019 19:29 by derekcyril

Surely ,plugging in motorhome / caravan outside house is same as using club sites ? give me a clue what TN~C~S means cheers ,derek

Posted on 11/01/2019 21:57

Caravan sites are not allowed to have the same wiring system that you find on most houses because of the risks that I have mentioned. I am referring to what is known as PME (Protective Multiple Earthing). In this system what we call “earth” i.e. all the metalwork in the house, can experience a high voltage under certain fault conditions. This doesn’t matter in the home because everything that is “earthed” is at the same voltage but when your van is outside the house there is a difference between the van earth and the real earth.

In  the case of an electric car being charged on the driveway of your house, the metal of the car is connected to the metal in your house but if you were to touch, say, a metal fence at the same time as the car there could be a difference between the two which could give you a jolt. As a result of this the new regulations require some specific installation rules.

I was not looking to stir up a lot of technical argument and debate, I was hoping that somebody would come along and clarify the regulations. I have my motorhome on the drive, my house is on a PME (TN-C-S) system and I plug the van into a socket in the garage. It would be good to know from an expert on the 18th Edition of the Wiring Regs to comment as there are some members who are Electricians and Electrical Engineers (like me).

I can see that my question has just caused confusion so it is probably better if I take it up with the Club direct rather than this forum.


Lutz replied on 12/01/2019 07:33

Posted on 12/01/2019 07:33

What is the difference between hooking up the caravan or motorhome to the household electrics and using any other electrical appliance such as a lawnmower in the garden, plugged into an indoor socket?

hitchglitch replied on 12/01/2019 07:44

Posted on 12/01/2019 07:44

A lawnmower is a Class 2 appliance and is double insulated. An electric car is Class 1 and has exposed metal (and so does a caravan or motorhome!).

I have taken this up on another forum and will also contact the Club. I believe it is a problem but is not covered by any of the Regulations. Will report back if I get any clarification.

Justus2 replied on 12/01/2019 08:24

Posted on 12/01/2019 08:24

I have experienced a similar related problem a few years ago now, during my time playing in a local pub band.. Pubs can have some quite historic and quirky additions to their mains sockets and wiring.. There is often an odd socket which although on the ground floor can be a spur from the upstairs ring main... If the guitar amplifier is plugged into the downstairs ring main and the PA ( microphone ) amplifier is plugged into the upstairs spur, if you then happen to have hold of a guitar and your mouth touches a microphone you can sometimes feel a tingle to put it mildly.. Having been caught out a couple of times over the years, usually in older pubs, I became very cautious to make sure we were drawing all our power from the same double socket which easily coped with the total load, but it at least made sure we all had the same earth.....wink