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

 

[St3v3]

. 4 ohms is too high for things which are supposed to be connected,

No, his leads probably measure a couple of ohms lol.

 

[Gromett]

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.

I disagree. If he is getting a shock then there is something wrong either in the design/implementation or a failure after.

A vehicle electrics should be designed in such a way that it cannot give a shock under pretty much any operating condition.

 

[Raul]

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

Unless you are static, and close to supply. That’s why you need good continuity back to supply, like in any other extension lead.

 

[Raul]

Does anyone carry an earth rod with their own connection?

Not suppose to, unless you are static, and your earth rod has to be close to supply , and tested for low resistance to be effective.

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[Raul]

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!

Only for few milliseconds and red will trip, any metal chassis, like washing machine, boiler, van, table saw etc, the metal chassis that can be touched, it has to be earth bonded.

 

[DBK]

View attachment 815802
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.

I think you need to repeat the test on another site to see if you can eliminate the possibility the problem is site-specific.

 

[TravellingSmurff]

I think you need to repeat the test on another site to see if you can eliminate the possibility the problem is site-specific.

The only test that proved there was an issue was me touching the metal and getting a shock. I didn't want to try that again.

 

[TravellingSmurff]

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.

Worked as in same result. Plugged the lead into the ehu and the other end I stuck my multimeter in and with the other multimeter lead, stuck that in the earth of the plugs in the van, touched the earth on the battery charger etc and all showed the same resistance. Indicating continuity.

 

[DBK]

The only test that proved there was an issue was me touching the metal and getting a shock. I didn't want to try that again.

Use your multimeter between bare metal on the van and a bit of wet earth. You could improve the measurement by using a tin can or something metal resting on the wet earth to give a larger surface area, then touch it with one of the multimeter probes with the other contacting the vehicle.

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[Bodoge]

View attachment 815802
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.

It means, that you have an earth leakage and the earth via the mains cable isnt connected to either ground, if it is, then the earth cable isnt connected to the apperatus that is causing the leakage.

 

[Tigger-Tim]

Worked as in same result. Plugged the lead into the ehu and the other end I stuck my multimeter in and with the other multimeter lead, stuck that in the earth of the plugs in the van, touched the earth on the battery charger etc and all showed the same resistance. Indicating continuity.

I'm still can't quite envision what you've tested. But if it's from the earth pin on the end of the lead to points that should be earthed in the van, then 4 ohms is MUCH too high.

 

[tonyidle]

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!

Earth is just a convenient term and doesn't necessarily refer to the muddy stuff underfoot. The mains earth MUST be connected to the vehicle chassis. In the event of a live contact with vehicle metalwork the RCD will operate and (if all is well with the incoming supply) the circuit breaker will operate as well. The alternative, with no chassis connection to the mains earth, is that the whole vehicle is live when a fault occurs. This may be advantageous in that it stops illicit callers in their tracks. Less so for the occupants unless they jump, rather than step, out.

 

[Roger J Holman]

I am very sorry, but it my firm and long held belief that the vehicle electrics ,12volt, should be insulated/isolated from the mains voltage in every respect. There should be no chance of the vehicle chassis, or body, coming in contact with mains voltage, through an Earth cable, or through a 'leak'. To have such a contact occurring gives rise to the possibility of death by electrocution.

Vehicle electrics are a stand alone system. The mains earth should NOT be connected to the chassis, it should be connected to the MHU earth via whatever set of equipment it in use, RCD , consumer unit, and mains plug.

OP. Get hold of a reliable, qualified, knowledgable real electrician and pay him what he asks to remove the risk to your life, and that of your loved ones.

 

[autorouter]

If you are trying to measure a low resistance, you need to switch the multimeter to its lowest range, which I think from your picture is the 200 Ohm range. Before you take a measurement, see what you get when the probes are not touching. The display will probably say 'Overload' or some abbreviation like OVLD or OL, which means the resistance is too high to measure on that range. Then press the two probes together to see what the reading is. Usually about 0.3 ohms, which is the resistance of the test leads. Now you can measure the thing you want to know the resistance of. Whatever the reading is, you can subtract the resistance of the test leads to give you the resistance of the thing you are testing.

If you are trying to measure a high resistance, switch the multimeter to the highest range, which I think from your picture is 2000k ohms (= 2 Megohms). Before you take the measurement, press the two probes together to see what the reading is. It should be zero ohms. When the probes are not touching, you should see 'OVLD' or OL', ie resistance is too high to measure. Now you can measure the thing you want to know the resistance of.

So imagine you want to see if the insulation between two wires in a hookup cable is satisfactory. Switch the multimeter to its highest range. With the cable unplugged at both ends, touch one probe on the neutral pin and the other probe on the earth pin. The display should read 'OVLD' or 'OL' all the time, and shouldn't show anything else. The resistance should be higher than the highest reading an ordinary multimeter is capable of reading.

To see what the actual insulation resistance is, you need a more expensive meter, as Tigger-Tim has explained. However if your ordinary multimeter gives an OL reading, that's a pretty good indication that the insulation is likely to be good.

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[tinkertaylor]

I wish posters who don't know anything about electrical systems would stop posting their opinions and let the other posters, who obviously do, post their thoughts.

This is a dangerous situation and posting huge posts on the merits of multi meters and continuity just dilute the qualified posters who could help.

If the poster doesn't know how to use a multi meter then his attempts to find this fault, which have led him to plugging it back in! Is going to end in disaster..

 

[autorouter]

The only test that proved there was an issue was me touching the metal and getting a shock. I didn't want to try that again.

In my opinion, vehicle electrics and hookup post electrics are designed so that a single fault will not cause a life-threatening situation. The fact that you have had a shock from touching exposed vehicle metal means to me that there is more than one fault. Maybe one fault has been present for a while, and plugging into a faulty hookup supply or cable made two simultaneous faults that made the situation dangerous.

By all means do some tests on isolated items like the hookup cable or the easily accessible parts of the vehicle electrics. But if you don't find a couple of obvious faults, get the whole thing looked at by a competent motorhome electrician. An auto-electrician or an electrician who works just on domestic systems may not have the necessary experience in the ins and outs of motorhome 12V and 240V wiring.

 

[68c]

I thought europe does not have neutral tied to earth, odd you are getting a shock. Thought you had to touch both neutral and live.

 

[Mark and Mindy]

I am not qualified to give advice so this is just for your information and could help you to ask the correct questions...

It could along the lines of a diverted neutral current fault with the site electrical installation.

These faults are very difficult to diagnose but there could be nothing wrong with the van.

 

[meanders]

Another very technical forum I frequent always comes back with "if you have to ask, you don't understand enough to do it" for anything safety related.

Let's look at worst case for a moment. A third party gets seriously injured or killed. The OP would be prosecuted, as might the converter, lead supplier or the site owner. Saying you took advice from an internet forum would be zero defence in front of a judge.

I could ramble on about the differences between earth, earthy, and floating neutrals but it adds nothing.

Please just get a professional to sort it out.

Remember mains level electricity kills.

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[Bodoge]

Another very technical forum I frequent always comes back with "if you have to ask, you don't understand enough to do it" for anything safety related.

Let's look at worst case for a moment. A third party gets seriously injured or killed. The OP would be prosecuted, as might the converter, lead supplier or the site owner. Saying you took advice from an internet forum would be zero defence in front of a judge.

I could ramble on about the differences between earth, earthy, and floating neutrals but it adds nothing.

Please just get a professional to sort it out.

Remember mains level electricity kills.

As ive already said. One if the 1st things i was taught as an apprentice spark 60yrs ago was that, Live can kill you, Neutral can kill you but earth will save you, respect all. 2nd was Dont meddle with what you know little about.
I have also seen horrendous injuries from a 12v dc battery where body parts were lost. Just because its low voltage doesn't mean its less dangerous, even those qualified to meddle have to maintain respect or face the consequences.
My advice, respect yourself, get a professional .

 

[meanders]

but earth will save you

Great advice and similar to what I was told as an electronics apprentice. However there is a caveat. You don't want to be connected to anything live and then touch earth. Working with 1000's volts RF, we had to be very careful with earth.

 

[autorouter]

It could along the lines of a diverted neutral current fault with the site electrical installation.

These faults are very difficult to diagnose but there could be nothing wrong with the van.

I appreciate the possibility of diverted neutral current in domestic properties that have metal pipes going into the ground as well as the earth connection back to the substation. but there is not really any possibility of that in a mobile motorhome installation. Even a static caravan wouldn't have that problem, all the pipes are likely to be plastic, with no mains gas pipes. It may be a real problem in other scenarios, but it doesn't affect motorhomes.

 

[Bodoge]

Great advice and similar to what I was told as an electronics apprentice. However there is a caveat. You don't want to be connected to anything live and then touch earth. Working with 1000's volts RF, we had to be very careful with earth.

The biggest machinery i ever worked on was a shipsplate bending machine that could bend 1" steal plate like we fold paper. Only 415v backed up by 500A fuses, one of which i managed to blow, lost a stanley screwdiver with an 8mm x 100mm blade. Most of the metal embedded itself in my face and neck and all facial hair was gone. All i did was lever a cable in the isolator out of the way of a cable entry. Taught me a lesson, dont take fuseboard legends as gospel.

 

[Tigger-Tim]

My father had 33,000 volts to his bench at MEB. Current limited to safe levels, but the cleaners still gave his area of the lab a wide berth!

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[EML]

My father had 33,000 volts to his bench at MEB. Current limited to safe levels, but the cleaners still gave his area of the lab a wide berth!

And Van de Graaff generators; even toy ones are 200,000V. We had one at school, but I guess schools can't afford £150 for one of these nowadays.

 

[EML]

I'm still can't quite envision what you've tested. But if it's from the earth pin on the end of the lead to points that should be earthed in the van, then 4 ohms is MUCH too high.

TravellingSmurf's (how do you reference someone in a post?) meter is a SinoMeter M830B. Farnell sells this at £2.95 one-off, with the 'SinoMeter' scratched off, which is probably pertinent to your observation.

@TravellingSmurf: I'm an engineer, and my last multimeter cost £220. However, I would think twice before using this to try to locate a potential mains safety issue in my van. Don't get me wrong - cheap Chinese kit has its place, and I have some, but it's horses for courses.

 

[EML]

I wish posters who don't know anything about electrical systems would stop posting their opinions and let the other posters, who obviously do, post their thoughts.

This is a dangerous situation and posting huge posts on the merits of multi meters and continuity just dilute the qualified posters who could help.

If the poster doesn't know how to use a multi meter then his attempts to find this fault, which have led him to plugging it back in! Is going to end in disaster..

This. motorhomefun is pretty much useless if you need electrical/electronic advice. There are several people who know something useful, and several others who know exactly nothing, but who are quite happy to post their incorrect/dangerous/dumb advice. Any 'normal' person has no way of distinguishing between them.

 

[Bodoge]

This. motorhomefun is pretty much useless if you need electrical/electronic advice. There are several people who know something useful, and several others who know exactly nothing, but who are quite happy to post their incorrect/dangerous/dumb advice. Any 'normal' person has no way of distinguishing between them.

I have put a notation on my Avatar, to give a clue to my trade albeit ive been retired 12 years, the regs have changed but electricity is for the trained. My meter is an isoTech IDM 72 a good bit of kit, around £200 at RS.

 

[Widge]

I have put a notation on my Avatar, to give a clue to my trade albeit ive been retired 12 years, the regs have changed but electricity is for the trained. My meter is an isoTech IDM 72 a good bit of kit, around £200 at RS.

I had an Avo 8 for many years, but not very convenient to put in a toolbox so flogged it, i have had a mid range Iso-Tech digital multimeter for the last 32 years ( i think it cost about £120 then) it still works fine for everything that I need it for, I do check it occasionally to check if the readings are ok, it always seams to be ok.

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[tinkertaylor]

I passed my inspection and test over 10 years ago, 2391. Multimeters are great for certain things but to find these type of faults, thoroughly and to the wiring regs, you need an Insulation and Continuity Tester that can test upto twice the working voltage, in this case its 500 volts.

230 volts when used outside is deadly, be very careful. I have friend who was a fireman that attended a fatality caused by faulty wiring, in a child's back garden.

The conditions the OP has outlined show the steel work on his van live, anyone can touch the outside of his van........