Safety Issue - connecting to mains at home?
I had my caravan connected to the home mains supply via a cutout device as I have done for years. I needed to move it slightly and happened to touch the wheel hub and the ground at the same time and got a slight electric shock. Checking this with a voltmeter
I found there was a voltage of nearly 80 between the hub and the earth.
My caravan supplier checked the van and found no fault and thought there may be an issue with my supply at home. Checking this out I found there was a voltage between the earth and neutral connections. This is apparently normal for house supplies using Protected
Multiple Earth (PME) systems.
Caravan club guidance in this leaflet http://www.caravanclub.co.uk/media/1022895/mains-electrical-installations-mo.pdf says this is OK and makes no mention of PME. Yet an electicians website https://www.tlc-direct.co.uk/Book/7.9.1.htm says caravans should
NOT be connected to a PME supply - one like in caravan sites with separate earthing arrangements should be used.
So is there a safety issue here? There are plenty of people selling leads for connecting your van to the home supply.....
Comments
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It's a while since I looked at this but I believe that PME systems are used in areas where it is difficult to get earth continuity back to the substation. The neutral (outside of the installation) is connected to earth to give a route back to the substation. The problems occur if the neutral is not properly connected or goes open circuit so the earth can then become live. The problem with the caravan is making sure that all parts are properly bonded and securely connected to earth and relying on the earth conductor in the EHU cable may not be sufficient.
I appreciate that this doesn't answer your question directly although a small earth to neutral voltage should not normally be a problem. Will try and do some more research.
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The Wiring Regs. forbid a caravan park and caravans within it from using a PME system. It seems also that caravans should not be connected to a PME supply but maybe this is meant to be in the context of a caravan park rather than in the home environment.
There are two main reasons as far as I can see. Firstly, there many be a voltage between the caravan metalwork and the "true earth" that the caravan is standing on. Secondly, the caravan bonded metalwork will carry fault current as it is connected to the neutral return.
As usual with these situations it is impossible to say whether this is a real problem or just a theoretical problem so unfortuanately I cannot contribute any more on the topic but I think it is a serious enough discussion to raise with the Club and see if one of their technical forums can assist. Not sure how to do this.
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Interesting as we live on top of a hill that is made of sand, which in summer dries out, so for the 40 years we have been here have had a PME system. But we have external power to the garage and for 30 of those years from there to a caravan. Initially the
van was via a RCD plug.Probably 25 years back the Utility did some checking and installed a supply RCD so I dropped using the domestic plug type RCD. The utility people made no point about the van during their looksee and modification.
Is the van's supply safe on the RCD protected system?
Clearly we can't earth anything as that will potentially trip the RCD.
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From an electrical point of view, the connection to the caravan is a spur the same as one in the house or to the shed etc. There are many appliances where a faulty earth will reslt in the neutral voltage being transmitted to a metal case, electrically the
same as a caravan.When the caravan in question was checked at the dealer it was probably checked using the dealer's cable. I wonder if the cable or its terminals are faulty.
Why not obtain a tester such as those sold by caravan dealers for checking polarity. These are easy to use and will show a fault in any of the sockets in the van and in the house.
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Thanks for the comments to date. All cables have been checked and the dealer used a supply just like those used on caravan sites which is why he could not find an issue. In fact I tested it myself on site using my own meter between the caravan connected
there and the ground and there was no voltage at all.There is certainly no problem with polarity with my home supply or the connecting cable and I have checked the bonding of the system to the home PME terminal where the power supply comes into the house and it is as designed.
As stated originally, I only got a tingling sensation but 80 volts seemed unusually high to me. If it had been say 10 volts I would not have felt anything. And I suspect I only experienced the shock because it was a rainy day and I happened to touch the
wet ground and wheelhub at the same time. Assuming the whole caravan was 'live' as I suspect, you would normally be wearing insulating shoes which might explain why nobody else has noticed this.I do not expect to be fried alive but it does raise the question of whether it really is safe to hook up a caravan at home without a separately grounded supply.
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By no means can I say I understand the ins and outs of electrickery, but we were advised that we should NOT plug our caravan into the ordinary socket in our garage without first having an RCD in between, we were also advised that if we ignored this and were
unfortunate enough to have a fire in our house and it arced to the caravan via said cable - our insurers would most likely invalidate our claim !!!Needless to say we installed the RCD sharpish
Alison
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Reverse polarity is a red herring in this instance and won't affect the fact that you have a "touch voltage" on the caravan metalwork. With the PME system it is possible to have a voltage on the neutral as a result of what is happening on the rest of the
network. Your house's neutral is connected to the house's protective conductor which, although referred to as the 'Earth', is actually just a wire which is connected through your EHU lead to the caravan chassis. What you are experiencing is a voltage between
your chassis (which you assume to be "earth" but which is not) and the real earth or ground. Inside the house you would probably not experience this due to insulated flooring etc.Is this a problem? Sorry, although I am a qualified electrical engineer who once sat on the IET Wiring Regs. Committee, I cannot give you a straight answer. I suspect not but it really needs somebody with expertise in this type of system. 80 volts in wet
weather is getting a bit higher than I would like.If it were me I think I would only plug into the EHU to cool down the fridge before leaving home (it's not good for the battery anyway to keep the EHU connected). Then I would try to find an expert!
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Re earlier comments, I have checked the polarity of the supply and it is correct.
I have found a place on this site for 'consulting the experts' so I will email them and refer to this thread and see what advice they can offer.
Thanks again to everyone who has responded.
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Re earlier comments, I have checked the polarity of the supply and it is correct.
I have found a place on this site for 'consulting the experts' so I will email them and refer to this thread and see what advice they can offer.
Thanks again to everyone who has responded.
If you come up with anything definitive, please let us know, as this could affect many of us.
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When you said that you measured the voltage between the wheel hub and "earth", which earth did you use? i.e. a spike in the ground, other metalwork ......etc.
I am assuming of course that your caravan is correctly bonded and that the protective conductor (earth wire) is present in the EHU cable and connected to the earth terminal in your house socket and that this socket earth terminal is correctly bonded to the
rest of the house earth system. The fact that you have a PME system doesn't affect the need to have the house metalwork, piping etc. properly bonded.0 -
Have just checked our van stored at home and connected to electrical supply in garage, tested van sockets with a 'martindale' plug in tester and all o.k.
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, AND ,,and when in the past used a 'genny',i put an earth spike in the ground too !!0 -
I am assuming of course that your caravan is correctly bonded and that the protective conductor (earth wire) is present in the EHU cable and connected to the earth terminal in your house socket and that this socket earth terminal is correctly bonded to the
rest of the house earth system. The fact that you have a PME system doesn't affect the need to have the house metalwork, piping etc. properly bondedThe earth bonding cable had a 1/8" gap under the nut on our van even though it was supposed to have been PDI'd when new
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The 80V Potential difference could be due to the caravan being outside the main equipotential zone. I would disconnect your lead at the caravan end and measure from the earth terminal in the trailing socket to the earth where you tested before to see if
there is a potentail difference.Then check between neutral and earth terminals in the trailing socket to check that the neutral earth link is made back at the incomer. there should be 0V between them if there is higher than that then you have a bad Neutral - earth connection.
you mentioned in your post you measured a voltage between neutral and earth what was it?
Also check your Live to Earth voltage it should be exactly the same as your Live to Neutral voltage.
it sounds to me the problem is on your house .
To me it doesn't mattter the type of earthing system the caravan is plugged into, an electric cement mixer would have the same problem ,as its also made of metal.
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The 80V Potential difference could be due to the caravan being outside the main equipotential zone. I would disconnect your lead at the caravan end and measure from the earth terminal in the trailing socket to the earth where you tested before to see if
there is a potentail difference.Then check between neutral and earth terminals in the trailing socket to check that the neutral earth link is made back at the incomer. there should be 0V between them if there is higher than that then you have a bad Neutral - earth connection.
you mentioned in your post you measured a voltage between neutral and earth what was it?
Also check your Live to Earth voltage it should be exactly the same as your Live to Neutral voltage.
it sounds to me the problem is on your house .
To me it doesn't mattter the type of earthing system the caravan is plugged into, an electric cement mixer would have the same problem ,as its also made of metal.
The OP measured from the caravan chassis to "earth" not neutral to earth and it was 80 volts as it says in his posts. Agree that there cannot be a voltage between the neutral and earth cable (protective conductor). I assume that he measured between chassis
and real earth e.g. a spike in the ground. In a PME system the neutral can float above real earth because of high resistance in the subsoil.In large industrial sites and dry locations we used to create several earth points deep in the ground. This was to reduce the possible touch voltage during lightning strikes. Same problem.
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Interesting as we live on top of a hill that is made of sand, which in summer dries out, so for the 40 years we have been here have had a PME system. But we have external power to the garage and for 30 of those years from there to a caravan. Initially the
van was via a RCD plug.Probably 25 years back the Utility did some checking and installed a supply RCD so I dropped using the domestic plug type RCD. The utility people made no point about the van during their looksee and modification.
Is the van's supply safe on the RCD protected system?
Clearly we can't earth anything as that will potentially trip the RCD.
Ocsid, there is no difference in bonding requirements on a PME system. The more earthing the better. The rcd is just a coil around the live and neutral conductors and under normal conditions the same current flows through both wires and cancel out. If you
get a fault to earth or if you touch a live wire whilst standing on earth, a current flows from live to earth rather than live back through neutral. The rcd detects the imbalance in a few milliseconds and trips the supply.0 -
he did say he measured chasis to earth .
I am asking him to measure neutral to earth voltage to ensure they are at the same potential.
I can't see him braying a spike into his drive to test it.
more chance of finding the water main.
I would do the same test as he did before but from the lead earth terminal to the ground at the same point he did it before with the caravan disconnected , if he gets the same result the problem is not with the caravan
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I had a friend who was a Fireman - and he thought it was great when I lost one of the "feet" off the corner steadies. Leave it was his advice so the caravan was permanently earthed in case of something going wrong. I still do it - not sure if it's really
correct but it made sense to me.0 -
Judging by this forum, there is at least one person who drives a spike into the ground and connects an earth when they pitch up. I make no comment.
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I had a friend who was a Fireman - and he thought it was great when I lost one of the "feet" off the corner steadies. Leave it was his advice so the caravan was permanently earthed in case of something going wrong. I still do it - not sure if it's really
correct but it made sense to me.When I looked under my caravan the legs were mounted on the caravan floor not on the chassis so they would have been earthed.
Just had a similar conversation in the electrical suppliers today about Firemen giving electrical advice.
In most cases you would be better off asking a bus conductor.
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I had a friend who was a Fireman - and he thought it was great when I lost one of the "feet" off the corner steadies. Leave it was his advice so the caravan was permanently earthed in case of something going wrong. I still do it - not sure if it's really
correct but it made sense to me.When I looked under my caravan the legs were mounted on the caravan floor not on the chassis so they would have been earthed.
Just had a similar conversation in the electrical suppliers today about Firemen giving electrical advice.
In most cases you would be better off asking a bus conductor.
Yep, have to agree, been married to a fireman for years and the one thng he will not mess with is electrics, he always says..." don't mind gas, you can smell that, but electricity you don't know about it until you wake up (hopefully) after hitting the wall
behind !"Alison
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"When I looked under my caravan the legs were mounted on the caravan floor not on the chassis so they would have been earthed."
Don't the plastic "feet" on the corner steadies mean the caravan isn't earthed? As I understand it if a car is accidentally hitting a live wire is safe enough untill you go to get out of it.
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It is true that a car is effectively insulated from the ground which is why you can sometimes get a belt from static build-up when exiting the car. You used to see cars with earth straps dangling down onto the road to dissipate any static. Maybe the modern
car construction contains materials that are not prone to static build-up.0 -
Thanks for the ongoing comments.
I will make some further measurements and report them if it ever stops raining. I don't feel inclined to poke around with cables while it is bucketing down.
As to how I made the measurements, I had a multimeter which has two metal probes. I poked one probe into the soil a foot or so off the drive (which was very wet) and touched the other one on the wheel nut.
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Brian,
1 st test I would make would be to check voltage from neutral to earth in your fuse box, it should be zero.
check by testing live to nuetral 1st you should get between 230V - 240V with your meter on the AC setting.
then check live to neutral you should get exactly the same reading.
that will prove your meter is reading.
if they are not the same and you then check netral to earth and the reading is greater than 0V you have a problem.
post your results on here .
if all is ok your problrm could be further down the line towards your caravan.
good luck with it.
If your not confident , get a spark in.
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Following the last few posts I have done some indoor checks and have found a problem. I started by checking voltages at the fusebox and these were as expected. 240v between live and earth, 240v between live and neutral and 0v between neutral and earth.
I repeated these tests at the socket with the RCD which I plug the caravan lead into and was surprised to find that there was 0v between live and earth..... Hmmmmmm...
So I traced the cabling back and found that the idiotic fitter who connected a new electric garage door opener a couple of years ago managed to disconnect the earth conductor going from the spur for the door opener to the socket where the caravan plugs in. I
fixed that and the voltages on the socket are now as expected.I still have to check whether this has fixed the original fault by plugging the caravan in and testing there. Hopefully I can do that later this afternoon as the rain seems to be easing off. It is not very re-assuring to know that the 'safety' socket is
indifferent as to whether there is a sound earth connection ....0
