Motorhome or Caravan on EHU at Home
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.
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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.)
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It’s clearly not practical to connect the motorhome to an earth rod so it’s a question of don’t do it, don’t touch it or ignore the problem as low risk.
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I didn't understand any of that. Is ignorance bliss?
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Earthing systems, CY, and yes - probably. ⚡️
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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.
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Surely ,plugging in motorhome / caravan outside house is same as using club sites ? give me a clue what TN~C~S means cheers ,derek
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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.
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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.
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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.....
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The link explains it very well. I am aware of the requirements for electric vehicles, my point being that a car and caravan is much the same and although not directly covered by the Regs. still has the same safety risks.
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My garage is wired into the house mains, and my garden shed is wired from the garage via a further MCB. My EHU cable goes from the caravan and into the shed, using an adaptor cable to convert it to fit a 13-amp socket in the shed. This keeps the battery on trickle charge through the caravan charger unit, and the caravan 240v electrics can be operated in the same way as when on a club site EHU. The multiple earthing of metal pipes in the house have nothing to do with the electrical installation, other than the earthing point for both the installation and the MPE's is sound. Unless you are using equipment specially capable of generating high voltages, there will never be an electrical path capable of producing more than the nominal 240v of the mains supply.
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Oops, the earthing of metalwork etc. in the house is an integral part of the electrical installation and you have entirely missed the point. Firstly, this thread ONLY relates to houses on a PME system, although this is extremely common. I don’t know what your house is, you haven’t told us and probably don’t know. Secondly, it concerns the fairly rare (but quantifiable) risk where a PME distribution system suffers an open circuit neutral which can cause your house neutral, hence your earth and all the bonded metalwork, to have a raised voltage which in exceptional circumstances could be 240 volts. This is a fact, not speculation.
Unfortunately, it therefore follows that if you plug your van into a socket in your garage, shed, or whatever, the outside metalwork of the van under these unusual conditions can have quite a high voltage (I stress that this is only on PME TN-C-S systems). If you touch this whilst in contact with the mass of earth, metal fence etc. then you may experience a shock which no RCD can protect you against.
I have been in touch with various experts on another forum and conclude that what I am saying is absolutely correct and that you shouldn’t be plugging your van into an indoor socket for these types of installations. There is a genuine, albeit small, safety risk which for now I personally will note but continue the practice.
I was hoping that an expert would come forward but it is a specialist subject which needs detailed knowledge of the Wiring Regs. plus installation experience. I will contact the Club this week to ask if they have issued any guidance and whether they have any concerns.
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DD, it happens when a cable becomes disconnected in the distribution linking your house with other houses back to the substation. Although it doesn’t happen too often, designers know about it and design for it. So for example there are special installation requirements for outbuildings. Also caravan sites, marinas etc. are excluded from using PME due to the risks.
The Regs. don’t cover plugging in vans as I have described but I believe there is a risk which probably needs wider publicity.
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A Frame, wheels, steadies.
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On airfields, motor vehicles that may come in contact with aircraft have a trailing earthing strap in contact with the ground. While this is provided to discharge static electricity it would have the same end effect by earthing the vehicle.
I'm perfectly safe with the caravan plugged in as no PME here. All fixed wiring in conduit, lots of which is buried in concrete floors or chased into brickwork.
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You mean that yours is missing? The earth wire in the hook-up cable is connected to the metalwork of the van/motorhome and through the lead to the earth system in your house or site bollard.
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I've never had cause to worry about the safety of my electrics in garage or garden shed, but have just tested them, and the caravan, with the tester I carry in the van and plug in one of the 13a sockets to confirm correct polarity and earth after connecting to the EHU. Everything working correctly. I have in the past checked them with a multimeter and found that both the neutral and the earth registered earth-potential.
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Good to know that you have tested your installation although the issue I am referring to has nothing to do with your installation, it is caused by a fault external to your property which can cause your house earthing system to be raised to 240 volts worse case.
If your motorhome/caravan is hooked up to the house when such a fault occurs then it’s metalwork will also be at 240 volts so if you were standing in a puddle whilst touching the metalwork (washing the van?) then you would have a problem. Fortunately fairly rare but frequent enough for the IET Wiring Regulations BS7671 to cover PME installations in some detail and ban them from caravan sites, marinas etc. Also very clear guidance on fitting chargers for electric vehicles outdoors (which prompted my investigation as I am about to have a charger fitted).
As I say, this only refers to a particular type of house installation, albeit extremely common, the faults are rare and the regulations do not cover it.
I have drafted a letter to the Club although at this time I am not sure who to send it to so will use their “chat” line to find out.
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Why not ring your local electricity distributor and ask them?
If a neutral fault occurs then yes, you can get high voltages but this is usually on the network's circuits and beyond your control
The networks companies are usually aware of such faults and rectify them ASAP. If it happens to you ring the emergency line immediately.
Perhaps you could continue with the extension cable from your house/garage and try not to worry too much about things that are beyond your control.
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Lightning is beyond my control but I don’t hide under a tree. You are trivialising a serious subject either because you are misinformed or for other reasons which I can guess but won’t say here. No need to phone my DNO; having done further research I understand the problem and the regulations but would like to know what the Club’s advice is.
I will report back if I get an answer from the Club but will make no other comment.
Thanks to all for responding.
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Early in my career I did work for a time on both 240v and 440v 3-phase installations. I agree with you HG on the trivialisation of a serious subject. I have always told anyone dabbling in electricity that it can be a good servant but a dangerous enemy. I live cable's bare ends look no different to those of a dead cable, but the difference is "electrifying" (for the trivial-minded) when you touch them.
Having moved on into engineering development for the remainder of my career, I am out of touch with today's regulations but I know where to find them if needed. And I do check for correct polarity/proper earthing every time I connect to an EHU. For France, (among worst offenders) I carry a short polarity-reversal lead. A few years ago, at the Le Verdoyer campsite, I had to repair the earth connections in the EHU box before I could get an earth on my caravan. This can be important because, if the box has multi-point EHUs, and all EHU earth pins are connected to each other but not to earth itself, back feed from a faulty van can cause another connected van to be "live".
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I live cable's bare ends look no different to those of a dead cable
That reminded me of an incident 35 years ago. I was moving a light fitting over the stairway and fit a 2 way switch for a friend who lived in a row of terraced houses. I pulled the lighting circuit fuses but left the mains on as his wife was baking. I took the cover off a junction box to change the light cable. As a habit that I took the precaution of testing the cable before disconnecting. It was live. Turned off all the power and checked again. Still live and power was from next door
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Ha, ha, EasyT. Reminds me of long ago when we lived in a terraced house. A neighbour said her light in the outside toilet wasn't working and probably a blown bulb. I offered to check it, but she said her husband was going to buy a new bulb and fit it at the weekend. But it wasn't the bulb. Someone in the next street had carefully hidden a cable through the rafters of the outhouse and into their own outhouse, and removed the light bulb to fit a bayonet connector on this cable in its place. Don't think the police were involved, but there were some fisticuffs exchanged.
Can you get these bayonet connectors now - I still have two in my 'odds-and-sods' box?
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