Mains electricity through motorhome chassis (1 Viewer)

Jul 4, 2010
1,194
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Essex / central France
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Hymer Star Line 680
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9 years
Our motorhome is parked up and plugged into power, all 240v devices are working correctly, no apparent problem.
This afternoon was checking tyre pressures and picked up a small shock off of a steel wheel rim, first for me getting a static electricity shock from a vehicle chassis. While adding air and checking tyre pressure again received more shocks but they increased in power and were becoming quite sharp.
One shock was a little like the shock (I think 60v) from a phone line, well it was 35 years ago anyway. So decided to try to measure if there was any AC power through the wheel rim, it measured 80v.
Got wife to switch the mains off and the reading dropped to 18v, switched on again back to 80v.

So a question. Is there a shortcut to where to start looking for the problem or is it a case of starting at the 240v input socket and going through everything from there?

I was involved with general vehicle electrics for 20+ years with own garage workshop and have rewired a couple of houses, but wouldn't call myself an electrician.

Any help gratefully received
 
Feb 27, 2011
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Isolate each circuit in turn. My van has two breakers which would cut the search in half. after that it will require disconnecting wires.. Good luck.
 

Flamenca

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Jun 21, 2013
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The 'mains' supply should be completely isolated from the chassis.
 
OP
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Jul 4, 2010
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The 'mains' supply should be completely isolated from the chassis.

Thank you Flamenca, I realise that but something is passing current to earth and mitzimad's suggestion above may be the worst thing for it to be. It's raining hard here for the next 2 days so maybe as the MH is outside I'll leave the testing until Sunday or Monday.
 

Tootles

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Yes, the charger in the Elektroblock only
Just had a trawl online. It seems the Elektroblock units suffer from poor or faulty earth connections. In effect, your becoming the earth for the unit. Now I dont know how these units are wired, or if in fact they are earthed to the chassis??????????? Could there be a possibility that your EHU earth is faulty, either cable, at the van, or even the house??
 
OP
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Jul 4, 2010
1,194
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Hymer Star Line 680
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Just had a trawl online. It seems the Elektroblock units suffer from poor or faulty earth connections. In effect, your becoming the earth for the unit. Now I dont know how these units are wired, or if in fact they are earthed to the chassis??????????? Could there be a possibility that your EHU earth is faulty, either cable, at the van, or even the house??

I guess any of that is possible, this may be a long process and thanks for checking all that out. I'll check which circuit the problem is on first or if it's one or both, then go back initially to the EHU supply socket and so on. I do have the Hymer wiring diagram so can study that while it rains.

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OP
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Jul 4, 2010
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No inverter, no aircon, no fans, no 240v oven or microwave, no tv, just the basic MH as it came in the standard form a 2006 Hymer B680 Starline comes in. There are 3 extra plug sockets but with nothing plugged into them.

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Emmit

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I had a similar problem last year when on hook up. I used the steadies to earth the van before I touched it.
Those very nice people at 'VanBits' talked me through checking.
(Assuming your RCB's are not tripping?)

Check the plug on your cable that plugs into the mains. You are checking to see if the Earth is connected properly.
If that is OK, check the plug that goes into the 'van, (assuming you are using a single cable and not as reel with a spur on it). Again see if the wires are connected properly and securely.
The next to check on the 'van where the cables are attached at the rear of the input socket where the electricity enters the vehicle.
Here's the words of VanBits.
"If it's all OK up to there then you need specialist help"

I was OK because I found one of the Earth connections on my Hook Up cable were hanging on by just a thread or two. On rewiring the plug, everything returned to 'Normal' whatever that means. Good Luck.
 
OP
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Jul 4, 2010
1,194
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Hymer Star Line 680
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I thought about it all overnight and came to the same conclusion of checking the input into the MH first, but as it's tipping it down at the moment and the ground is very damp will leave that for a couple of days.

Out of interest where did you place your probes when measuring the AC voltage?

+ to the wheel rim and - to the ground the MH stands on. It's a thin layer of gravel with soil underneath


to get 18v without ehu connected you must have solar running? sounds like its an earth problem from the electroblock and the voltage increases when ehu is on

no solar fitted yet but that's an interesting point of a residue 18v with the EHU disconnected.


Check the plug on your cable that plugs into the mains. You are checking to see if the Earth is connected properly.
If that is OK, check the plug that goes into the 'van, (assuming you are using a single cable and not as reel with a spur on it). Again see if the wires are connected properly and securely.
The next to check on the 'van where the cables are attached at the rear of the input socket where the electricity enters the vehicle.
Here's the words of VanBits.
"If it's all OK up to there then you need specialist help"

I was OK because I found one of the Earth connections on my Hook Up cable were hanging on by just a thread or two. On rewiring the plug, everything returned to 'Normal' whatever that means. Good Luck.

After some basic checking this may be the route I'll take but will test first. I do have another 2 EHU leads so swapping them may prove something to start, then the plugs and sockets.

Thanks to everyone, I'll certainly report back with whatever result I find, all this may be helpful to others.
 
Jul 6, 2016
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I've used a mains tester which plugs into a standard 240v socket. Mainly got it to test for reversed polarity but has been handy for checking the EHU cable. It checks for No Neutral, No Earth, Live/Earth reversed and Live/Neutral reversed.

Can also be used to check campsite bollards with suitable adaptor.

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DBK

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Why would you still get 18v when disconnected from mains????

Battery charger? Common with AC and DC circuits?
The OP said the electricity was switched off, not disconnected. If the switch is single pole (unlikely I admit) then it could be a neutral to earth fault as a neutral wire could well read 18v measured to earth. But that doesn't explain why it goes up to 80v when switched on! Very odd.

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OP
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Jul 4, 2010
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The OP said the electricity was switched off, not disconnected. If the switch is single pole (unlikely I admit) then it could be a neutral to earth fault as a neutral wire could well read 18v measured to earth. But that doesn't explain why it goes up to 80v when switched on! Very odd.

Yes correct DBK, it was switched off and not unplugged. Once it dries out I will take a longer more measured look at voltages and if they remain stable or drop off/increase. Along with other suggestions here I'm sure the fault area will start to become clear once I can get back to it.
 
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Nov 6, 2013
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Sounds like you've lost an earth somewhere along the way.
I would start at the beginning and logically work through the electrical distribution:
Swap the hook up cable for another, and see if the fault stays (fault within the motorhome) or disappears (faulty cable).
If still faulty - then check the EHU commando socket on the MH - check the connections to the back of it are still making good contact.
Then move along the circuit.

Be careful using yourself as a test probe. 80V is more than enough to remove someone from the gene pool :(

Where abouts in Essex are you ?
 
May 8, 2016
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It is always possible that there may be a problem with the supply earth, as if it is "floating" (poor or unconnected) then a detectable voltage could be induced.

Thus the first thing I would do would be to disconnect the EHU cable from the van before doing anything else (thus eliminating the van altogether) and then check the earth integrity of the supply cable. If there is still voltage present on the earth of the EHU cable whilst connected to the supply, then the fault probably lies either in the cable/connectors, or even in the house itself. That could explain with the RCD in the van hasn't tripped.

It is obviously important to get to the bottom of this problem, use of gas in the van could be risky, and any earth fault in the house itself could have serious consequences.

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OP
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Jul 4, 2010
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Be careful using yourself as a test probe. 80V is more than enough to remove someone from the gene pool :(

Where abouts in Essex are you ?

Usually in Rochford and some work in Rayleigh, but until end of August at our holiday home in central France. Will make all the checks with safety in mind, having too good a time at the moment to want it all to end just yet.
 
OP
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Jul 4, 2010
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It is always possible that there may be a problem with the supply earth, as if it is "floating" (poor or unconnected) then a detectable voltage could be induced.

Thus the first thing I would do would be to disconnect the EHU cable from the van before doing anything else (thus eliminating the van altogether) and then check the earth integrity of the supply cable. If there is still voltage present on the earth of the EHU cable whilst connected to the supply, then the fault probably lies either in the cable/connectors, or even in the house itself. That could explain with the RCD in the van hasn't tripped.

It is obviously important to get to the bottom of this problem, use of gas in the van could be risky, and any earth fault in the house itself could have serious consequences.

The supply socket for the EHU is in a large shed a short way from the house, going to trace the shed's power source at the house to check the connections as first step.
 
OP
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No earth into the shed!

There is a junction box in the loft of the house with power supplied by a 3 core cable from the kitchen. The overhead cable from the loft across the yard to the large shed is 2 core terminating in another junction box. There is no earth supply to the large shed junction box in any form.
Will connect the EHU cable to a house socket where I can prove there is an earth supply, but do have to wait for it to stop raining first.

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Feb 27, 2011
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I may be talking out of my Butt here. But in some installations neutral and earth are bonded. If you are on a 2 pin supply and the phase is reversed is it possible that the 220v is going to your chassis via the neutral line? It would be a pretty poor installation for this to happen. But have you got a phase tester or a phase swap adapter?

I doubt it is this, but might be worth a check.

I have literally just got up and my head is fuzzy so I may be out on this one, just a thought.
 
May 8, 2016
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I may be talking out of my Butt here. But in some installations neutral and earth are bonded.

Nope, you're not talking out of your butt. Neutral and earth are usually commoned at the 3 phase star point (generator and sometimes transformers), and in certain distribution systems, also at the point of entry to the property or even at the distribution board.

It is always possible that there may be a problem with the supply earth, as if it is "floating" (poor or unconnected) then a detectable voltage could be induced.

No earth into the shed!

Bingo.

As previously mentioned, this will be where your fault almost certainly lies. I strongly advise against using the shed supply until it is sorted out and also adding in a local "home made" earth from a grounding rod. (There are numerous reasons for this that which I won't go into, suffice it to say that it would contravene just about every safety recommendation going)

Best bet is to plug the supply cable into a known good socket (in the house), then test the van. I'm confident you'll find that the problem will have disappeared.

Your next challenge will be to rip out the two wire feed to the shed and replace it with a three core version, suitably earthed and connected to an RCD in the shed. As it is an overhead cable, you will have to be careful choosing what to put in, perhaps SWA (steel wire armoured) cable would be best? I'm sure someone here would be able to advise

I take it that this is in France? Somehow nothing about French electrical practices comes as a shock (pun intended)
 
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Feb 27, 2011
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Nope, you're not talking out of your butt. Neutral and earth are usually commoned at the 3 phase star point (generator and sometimes transformers), and in certain distribution systems, also at the point of entry to the property or even at the distribution board.

My first trade was as an Electrician but that was back in 1987 and I stopped doing it in about 1992. I did however learn under my dad who was an electrician from the age of 5 or so. I also worked at a Transformer factory.

Because it is a long time ago my memory of the theory and practice is dated and fading. I know enough and remember enough to fix stuff when I am hands on but remote is always much harder not knowing full information.

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