Help with testing to find why I'm getting shocked when on EHU

[TravellingSmurff]

Hi guys,
I have a converted crafter that I didn't convert.
When in France the other week, I went on ehu and touched the underslung gas tank and got a shock. Same when I touched the metal in the garage part under the bed.
I do not have an inverter.
I have two UK mains plug sockets
I have a battery charger connected to the ehu

I understand that when on ehu, the chassis and plugs should be connected to the ehu earth and that when I got the shock, I was laying on wet grass and I was the conductor to earth, rather than it going back to the ehu.
How and what do I test? I have a multimeter. And I understand there should be some resistance between the earth on the ehu and the things connected to it, including the chassis. Do I need to make up a long lead, touch the earth on the ehu IN and then start measuring the resistance on appliances?

If you think I should hire someone to have a look, then who and anyone know at what cost roughly?
Taking it back to the people that did the conversation is a possibility but they're the other end of the country and was hoping to save some time, money and effort really.
Thanks for your time
Danny

 

[autorouter]

surely the incoming 240 should be earth bonded to the vehicle chassis to prevent this

Yes that's right. So the question is, is the break in the earth bonding in the hookup post, the cable or the motorhome wiring?

 

[herald_400rl]

Does anyone carry an earth rod with their own connection?

 

[Tigger-Tim]

First I want to say thank you for all the comments. Cheers
I'm back home in the UK now. I just didn't try any ehu for the rest of the trip
I ordered one of the plugin testers and will test today.
I asked about the polarity thing on the French site and that wasn't the case this time. But I didn't know about that at the time. I since have ordered some cables from ebay.
I agree about the electrician, however I wanted to do the basic continuity tests myself first to learn and second to save some time, which hopefully will save some money too. However, I fully appreciate the "leave it to the experts" comments
I will update when I have had a look
Thanks again everyone

I'd suggest starting by checking the cable. Use the multimeter to check the wires, especially the earth. I'd also pop the covers off the connectors at each end and make sure they are tight. If you can easily open the socket where the mains enters the van, I'd pop that off and check too.

Then plug the cable into the van [but NOT into the mains]. Use your multimeter to see if you have a connection from the van body to the earth at the other end of the cable [should be very low resistance].

With the breakers in the van turned on [still not plugged into the mains], check from the van body to the live pin [should be no connection] and the Neutral pin [should also be no connection].

 

[Widge]

I would also report any findings back to the crafter, unless it turns out to be your own lead, if it is due to an error in their wiring or not coping with reverse polarity situation (which is common overseas), they should address the issue, and ensure that their other clients dont have the same issue.

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[pappajohn]

Does anyone carry an earth rod with their own connection?

Doubtful.
It needs to be 4ft long and place a pre-determined distance from the incoming supply.

 

[Abacist]

surely the incoming 240 should be earth bonded to the vehicle chassis to prevent this

No - surely this is very incorrect! If the mains is Earth bonded to the vehicle then the vehicle chassis becomes live with 240 volts in the event of a mains short or leak as the vehicle sits on 4 rubber tyres so no connection to earth. If you then touch the chassis you become the earth connection and get a shock if you are lucky or die!

 

[TheBig1]

The fact is that there is no functional earth in vehicles and the only earth is that supplied by the hookup lead. Often you find no earth on foreign sites with only 2 core wiring. It is more concerning that the chassis has gone live, as this indicates a wiring fault or a damaged wire shorting to the chassis or something that is wired to it

The other possibility is build up of static electricity being discharged when you touch the tank. The van is on rubber tyres so generally insulated, unless there are stabilisers deployed or a discharge strap

 

[EML]

This is interesting and seems divided on this whole forum. I thought this was the case because anything metal can be conductive and I assume having it connected to ehu earth was mean that is a better conductor that a human and therefore be good for safety. assumption, not an electrician
Thanks

On chassis grounding: there's a lot of confusion about this out there. There's a long way, and a short way, to think about this - this is the short way.

There are two ways to build your van:

1. Have 3-core cabling in your van connected to anything which requires mains, and occasionally join the earth wire directly to exposed metal surfaces, such as a cooker top, but exclude the chassis
2. Have 3-core cabling in your van connected to anything which requires mains, and connect earth to the chassis. You can now connect cooker surfaces, and so on, directly to the chassis or to a nearby earth cable.

Your house does (2) above, where the "chassis" is your pipework, and so on, which is connected to earth somewhere (the very short answer is that if it's good enough for your house, it's good enough for your van).

So what's the difference? In case (1), the chassis floats relative to everything else in the van. You're in a metal box which is at an arbitrary voltage relative to all the mains-powered kit inside. This may not actually be dangerous if you put one hand on the kettle and another on the chassis, because the chassis can't normally dump current anywhere, but I think it would at least be temporarily uncomfortable, and at least potentially fatal. Besides, it makes absolutely no sense to let the chassis float. It's a no-brainer; set it to the same voltage as earth.

See also section 7.5 of Victron's wiring safety manual for pictures showing the earth connection. These pics show boats but, as the text says, they're applicable to any mobile system.

 

[autorouter]

The van is on rubber tyres so generally insulated,

The rubber that tyres are made from contain substances (carbon etc) that make it slightly conductive. Enough to dissipate any static that would otherwise build up when tyres rub against the road. That problem was solved in the last century. Obviously they are not very conductive, but they won't hold a static charge.

The simple idea of bonding the chassis to earth is that if a live wire comes into contact with the chassis, then a large current will flow through the live conductor to earth, which will trip any MCB or blow any fuse. If there's an RCD in the system then it will trip even faster.

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[meanders]

Sorry helpful Funsters, but is it really worth the risk of someone being killed when the person is clearly out of their competence zone?
The OP needs to get professional help and not use EHU until they can do so.
Should someone with a heart condition, or even a small chid get a shock, it could well prove fatal.

 

[Nomad.]

Start at the site supply plug and go from there. Check ehu plugs for loose earth wires then move to the van. As above the 240v should have its own circuitry.

Ok,for starters rhe chassis is connected to the negative of the battery.The rubber tyres block the potential difference to earth which is considered Zero potential or ground or earth.This probably probably explains why you’re receiving shocks.When you connect to an electric supply the CCU unit is earthed through one of the 3 pins in your blue connector plugs.Another way of guaranteeing safe connection to 230 v is to run a 10 mm cable from a lug on the chassis to an earth rod,you can buy this item from TLC electric .I assume you have an RCD unit to provide circuit protection.This will Not trip as any current leakage to earth will not show up as no earth potential exists with your set up.Hope this helps.

 

[Pausim]

I assume you have an RCD unit to provide circuit protection.This will Not trip as any current leakage to earth will not show up as no earth potential exists with your set up.Hope this helps.

I don’t understand this bit because there is leakage to earth through TravellingSmurff when he touched his gas tank. Surely an RCD should have detected this because there would have been an imbalance between the supply and negative, some of the current was going to ground through the OP rather than through the second stage of the RCD.

 

[Tigger-Tim]

I don’t understand this bit because there is leakage to earth through TravellingSmurff when he touched his gas tank. Surely an RCD should have detected this because there would have been an imbalance between the supply and negative, some of the current was going to ground through the OP rather than through the second stage of the RCD.

I can think of a few possibilities...

If there was an earth fault at the site bollard (ie some mains on the earth connection), he'd get a shock without causing an imbalance between live and neutral.

or

If Travellingsmurff only made a bad connection to earth, the imbalance might not have been enough to trigger the RCD

or

The van might not have an RCD.

 

[TravellingSmurff]

Tested the cable and no resistance from the two plug ends on LNE. I checked and the wires are in nice and tight.

meanders I appreciate your thoughts, however I am not hooking up the ehu and testing that. I am just trying to do the basics to learn and understand in the hope I can save time and money with the electrician. I do appreciate the care and comment though. I have contacted the company that did the conversion and I will be booking it in. I just want to take the opportunity to learn

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[Bodoge]

Does anyone carry an earth rod with their own connection?

I used to when in france in moho, and still would if i ever take mine there. Have a home in france and have knowledge of their wiring systems. I have stated elsewhere on these forums that Barny Rubble designed the wiring accessories , ie sockets and switches.

 

[Tigger-Tim]

Tested the cable and no resistance from the two plug ends on LNE. I checked and the wires are in nice and tight.

View attachment 815116

meanders I appreciate your thoughts, however I am not hooking up the ehu and testing that. I am just trying to do the basics to learn and understand in the hope I can save time and money with the electrician. I do appreciate the care and comment though. I have contacted the company that did the conversion and I will be booking it in. I just want to take the opportunity to learn

Use that setting on the multimeter when you're trying to prove a high resistance (eg. between the earth pin and the live pin on your plug - things that you expect not to be connected).

To prove a low resistance (ie the earth end to end), move it to the lower resistance setting - about 6 o@clock on your tester). When you change it over, you will find that your lead does have some resistance. This is normal. A 25m cable will be around 0.2 to 0.4 of an ohm.

 

[Abacist]

Something with absolutely zero resistance usually means that there is a break in the connection as otherwise there would be some resistance as explained above which is the cable wire.

 

[Derbyshire wanderer]

Tested the cable and no resistance from the two plug ends on LNE. I checked and the wires are in nice and tight.

View attachment 815116

meanders I appreciate your thoughts, however I am not hooking up the ehu and testing that. I am just trying to do the basics to learn and understand in the hope I can save time and money with the electrician. I do appreciate the care and comment though. I have contacted the company that did the conversion and I will be booking it in. I just want to take the opportunity to learn

That is not the correct setting for continuity testing. You need an electrician who can insulation test the installation.

 

[Derbyshire wanderer]

All RCD's are double pole they work by detecting I balance of current between live & neutral.

They are not all the same and given the OP statement there is probably nothing fitted to detect current leakage. I do know how they work

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[Abacist]

Perhaps it would be a good idea for the OP to buy a book or two to develop his understanding of the electrics, both 12 volt and 240 volt. There are number available:-

Haynes do a workshop manual on Motorcaravans though you can only get this in paperwork form now as they only provide online manuals now.

https://www.amazon.co.uk/Caravan-Motorhome-Electrics-complete-guide/dp/0648319083/ref=sr_1_1?crid=2EYIJ46NU6PKP&keywords=motorhome+power+%26+electrical&qid=1695834991&s=books&sprefix=Motorhome+electrics%2Cstripbooks%2C72&sr=1-1

There are also good books on marine installations for yachts and canal barges/narrow boats which operate on the same principles as motorhomes with both 12 volt and EHU systems for when they plug in to the EHU at marinas.

There are also 120volt versions available from the USA for RV's.

 

[DBK]

Tested the cable and no resistance from the two plug ends on LNE. I checked and the wires are in nice and tight.

View attachment 815116

meanders I appreciate your thoughts, however I am not hooking up the ehu and testing that. I am just trying to do the basics to learn and understand in the hope I can save time and money with the electrician. I do appreciate the care and comment though. I have contacted the company that did the conversion and I will be booking it in. I just want to take the opportunity to learn

Has the problem you are experiencing only happened at this one site? If this is the case it is possible there is nothing wrong with your vehicle and the issue lies at the site.

It is possible neutral and earth are swapped around and if your earth is bonded to the chassis and you are experiencing the voltage on the neutral line which if there is imbalance might be for example 40 volts which if you are well earthed by wet grass you would notice as a tingle.

The other explanation is the site has a Protective Multiple Earth (PME) installation and the local earth connection has failed. The impact of this would be your chassis would rise to the neutral voltage which shouldn't be a problem but could be in certain circumstances of load imbalance as mentioned above.

The only way is to try another socket in another site.

 

[tinkertaylor]

That is not the correct setting for continuity testing. You need an electrician who can insulation test the installation.

This, you need an insulation resistance meter that can test upto 500 volts on a 230 volt system. You can then test between live and the van chassis and neutral and the van chassis, you have a connection somewhere hence the minor shock. The rcd on the supply from the campsite should have tripped if the earth from it is good and the van chassis is earthed to the supply.

 

[Parrot Face]

We had exactly the same problem some years back. I got shocks when touching garage floor. Dog shaded under van and his head touched chassis and squealed. Same effect as ect, electro convulsive therapy. He was very happy for weeks remembered that I'd told wife off for pulling ehu cable. Checked the wires and the earth cable had worked loose. .

 

[Roger J Holman]

I am not going to attempt to suggest a solution to OP problem I am not a qualified electrician; I have, however, spent years installing and modifying 12v & 240 systems on boats. I have not managed to kill anyone as far as I know. BUT 240 Volt systems are inherently dangerous if incorrectly wired/connected, and can kill anyone. It is even possible for a vehicle/van to be built with reversed polarity; we had two Hymers in which the 12v positive wire was coloured blue, and the 12v negative wire was coloured brown. On the 240 volt system fitted on the same van, the 240 positive was coloured brown, and the 240v negative coloured blue. Confusion reigned for some time, until I worked it out.
The only advice I would offer to OP is that it is worth an hour or two of the time of a competent qualified electrician to sort out if and where you have a problem.
When wiring boats, an overriding principle was that the 12v system and the 240 volt system NEVER joined each other, even at the earth connection. The outcome of ignoring this mantra could be, in the event of a fault, A. the 12v equipment becomes 'live 'with 240 volts, and destroys itself, B. the 12v equipment becomes live with 240volts and destroys you.
Bear in mind also that comparatively small currents/amperages can seriously damage the health of anybody who is using a pacemaker or similar

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[Rapido925M]

Something with absolutely zero resistance usually means that there is a break in the connection as otherwise there would be some resistance as explained above which is the cable wire.

Surely a break would result in infinite resistance?

Gordon

 

[Bodoge]

Surely a break would result in infinite resistance?

Gordon

Exactly. For the non electrical experienced motorhomer all you really need to establish is that you have cable continuity, which, in my opinion, has been confused with cable resistance. The multimeter in use here is very basic and doesn't have the more useful range of ohm settings and an audible buzzer, which is about all the lay person needs.
Motorhome power systems need the expertise of both mains power and auto electricians for the more complex problems, its a dangerous opinion the unqualified guess.

 

[TravellingSmurff]

Something with absolutely zero resistance usually means that there is a break in the connection as otherwise there would be some resistance as explained above which is the cable wire.

I think my multimeter shows -1 for that

 

[TravellingSmurff]

All the continuity tests I did worked. E.g. plugged the cable in and tested from the appliances and plugs and the same resistance on all tests ~ 4ohms. So I plugged it in, I know I said I wouldn't but the curiosity go the better of me, I plugged it into the ground and with the other I touched the metal garage, and it should 2v when plugged in and 0v when unplugged.
I would be interested in people's thoughts. But I have it booked in with the builders now. So we will see.

 

[Silver-Fox]

NOT MH RELATED: I came home one evening and my neighbour was complaining about getting shocks from his cement mixer (trough his thick rubber boots).
Eventually I worked out that the problem lay with his extension lead. To save money he made one himself using TWO CORE flex. He had connected the neutral wire to earth at both ends "because that is what the power company do - connect earth to one phase to give the neutral effect". OK: not sensible but understandable.
Unfortunately, he'd then cut through the cable accidently and used a bit of "school-boy science": connect red to black and black to red. He didn't want to explain why he thought he'd cut through just at the point where the wires changed colour!

IF you haven't worked out the consequences of his error, power was coming in via the red wire, changing into the black wire at his repair and then being connected to the earth at his socket. Then, of course, it went into the metal frame of the cement mixer.

Gordon

My mind just boggles at what some people will do

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[Tigger-Tim]

All the continuity tests I did worked. E.g. plugged the cable in and tested from the appliances and plugs and the same resistance on all tests ~ 4ohms...

I've no idea what you were testing, or what you mean by 'worked'. but that doesn't make sense. 4 ohms is too high for things which are supposed to be connected, and too low for things which are not.