Motorhome or Caravan on EHU at Home
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I can understand your dilemma regarding there being no regulations extant on connecting caravans or motorhomes to UK Domestic TN-CS /PME supply. This video describes earthing systems and may be of interest to those not familiar with the subject. Interestingly the potential problem with caravans plugged into house supplies is described!
Meanwhile why not zoom down to screwfix or other supplier and buy an earthing rod. Clamp the rod to any exposed chassis point using a thick cable eg starter lead. it's what we do on continental sites when our tester says 'no earth'.
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chasncath - Thanks for posting link to video.
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Excellent video which is a very good introduction to the subject. It also tells you how to find out if your house is PME (TN-CS).
You could earth your van using an earthing rod whilst it is connected to your home supply. Apart from the practicality, this may not achieve the desired result as it is difficult to get a low enough resistance to earth to produce a voltage of less than 70 volts under fault conditions. It probably helps though.
If you had a separate building, say, a shed with a metal structure there are specific regulations. This in fact is exactly the same as connecting a caravan/motorhome and sometimes the van could actually be used as a dwelling (people live in their vans when having house renovation projects done). In this case you convert your shed/van etc. into an isolated installation with its own earth rod and the earth is NOT connected to the house. This in fact is what installers are doing for EV chargers located outside and it is sometimes referred to a TT island.
I am about to write to the Club and will publish the results.
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Any information from the club would be useful.
The risk is as, as I understand it,, in a TNC-S system should the Neutral fail in a certain way then the Earth conductors could become live. It would need the Neutral to fail between the service head and the main supply transformer - ie further back up the chain.
It has been identified that this potentially poses a small risk with Car charging points and hence the new regs.
Is the Mains hookup earth actually connected to the van body I wonder?
I have a good friend taking his 18th edition exams this week and will ask him for an opinion.
Mike
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The van metalwork is all bonded to the van earth terminal which in turn is connected to the earth conductor in the EHU cable then to the house earth and bonding system. With the caravan or motorhome outside of the house “zone” a potential can therefore exist between the van metalwork and the general mass of earth.
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Thanks hitchglitch - I assumed the chassis was bonded to the earth terminal, but the metal skin must prove a challenge to bond as its all glued together.
But it seems we have exactly the same situation as a car charging point, but the regs insist on TT earthing for that and have ignored other "vehicles".
I have a reply along the lines of "interesting - I will ask the instructors if I can". If I get anything useful I will add it here.
As you say DIY earth rods are pretty hit and miss, and I am not sure I would trust that as being better than the potential problem with PME.
Have you posed the question to JW (who made the video) he appears very knowledgeable in this area.
Mike
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I do believe that the Regulations are quite clear and the risks well known so I don't think that there is any need to seek advice on that. The fact that the Regulations don't cover plugging vans into your house doesn't really alter the potential risk.
The question that I have for the Club is whether they consider that these risks are sufficient to consider advising people by way of a technical note or other guidance.
I have had a reply indicating that the Technical Manager of the Club will respond in due course. They should be in possession of far more information on the subject than I am able to access so it will be helpful to get a response.
I should stress, again, that the risk is quite low but I am concerned enough to exercise caution when I am plugged in at home. I will not be washing the motorhome with the EHU connected!
Most house built in the last 20 - 30 years are on a PME system as there are technical reasons for doing this and also cost considerations. Those houses fed from overhead lines are not, nor are some older properties.
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The electrician fitting our car charger tells me that there is now a lot of extra work as he has to fit earth rods to most installations due to a minor and recent change in the Regulations. Looking at the motorhome on our driveway he agreed that could be a far bigger problem!
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UPDATE
I am pleased to say that I have received a prompt and well considered reply from the Club’s technical department on this subject.
The Club are aware of the issues involved and in the past have discussed them with the industry trade association, the National Caravan Council. Although the situation I have described above can occur, the instances are rare and require a combination of adverse circumstances for any problems to arise. It is far more important to have a caravan which is designed, built and maintained to the appropriate regulations in conjunction with good hook-up leads and a sound house wiring system.
It is also difficult for the average person to determine what system their house is wired to, plus the not inconsiderable risk that they may attempt DIY solutions which result in a more unsafe installation than the problem they are trying to solve.
Personally I am not aware of any simple solutions anyway and know that when you look at electrical safety statistics there have been serious accidents caused by private individuals attempting to fix things – connecting the earth to the live in a 13 amp plug for example!
I agree with the Club’s advice and it is good to know that the issues at least are acknowledged even if there is no simple remedy.
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Exellent discussion , earth spikes ,wait till they put one through underground pipes ( used to happen ) on a tangent ,built extension to bungalow ,did all the work ,then sparky comes to sign it off . earfh bonding when you use plastic pipes ? he didnt get it either
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hitchglitch - good to know technical dept replied promptly.
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I once worked for a small company which supplied power generating equipment for fitting into vehicles -frequently Land Rovers. We also supplied 440v.a.c. units for fitting in ice-cream vans. One day, and owner of a fleet of these van phoned me to say one unit was faulty - the freezer kept tripping out. He said it was the unit, because when they isolated the built-in power unit and ran a 440-volt supply from the depot, the freezer worked fine. Then he did mention that they had to jump on and off the vehicle or they got a shock. Ah! I then asked if they also had an earth cable connected. No, just the three live cables. I told the owner to switch off the supply, connect an earth cable, then try the freezer again. As I expected, the MCB dropped out.
With all the older caravans around, and many reliant solely on DIY maintenance, I do wonder how we rarely, if ever, hear of campers occasionally getting a "jolt" when hooked up on campsites.
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Just to confirm the comments from Hitchglitch and what the club has said.
From an instructor running an 18th edition wiring regs course. The regs would not allow a TNC-S earthing system for a camp site but do not have any special requirements for hooking up at home. They DO have requirements for electric vehicle charge points at home.
Fiddling with home grown earth rods or similar is unlikely to improve anything and unless properly tested could be a bigger risk than the potential, but extremely unlikely risk of failure in the combined N and E in a TNC-S system.
So I for one will change nothing and connect up at home as normal.
Mike
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Correct. As to what action you wish to take that is entirely up to the individual.
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We were at a site near Shrewsbury with a new caravan when I decided to give it a clean. I was wearing wellies and had no issues at first. I then got out a step ladder to clean the top and climbed up holding on to the ladder, when I also put my hand on part of the van I got a shock, mild but still a shock. First I thought it was static but doing the same thing again produced another shock. I had an electric meter so I checked between the van and the ladder and there was a voltage, can't remember how much now. We stood clear of the van and checked the electric post and noticed it had been bashed. Called out the park owner and he immediately called in his Electrician. He found that the post had been hit by someone and it had dislodged the earth strap from the earth spike, after repair the van was at the same potential as the earth, no more shocks.
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Sounds quite dangerous.
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