Mains electricity through motorhome chassis (1 Viewer)

[veevee]

Problem solved!

0v at the wheel/chassis when switched on or off due to the simple fact of having an earth in the supply socket transforming the situation.
An hour ago measured the voltage at the road wheel with the same EHU cable connected to the same shed socket, 69.9v and 14.0v as a residual. Pull EHU cable out of socket and 0v.
Plug into a known earthed socket in the house and both readings are 0v.

Have since discovered we have 3 buildings all with no earth point but they are due to be either demolished or seriously repaired depending on the Brexit negotiations outcome. So in the same vein as all our other projects we have here in France we have decided to stop investing in what may or may not be our home in retirement until more is known. Providing this isn't a stupid idea I'll get three earth rods and wire each building into an RCB.

The unstinting expert help given by all on this thread is so typical of the goodwill here, a very big thank you indeed, and if we are here and you need an overnight on your way north or south we have plenty of space... but can't guarantee you can plug into the electrics!

 

[pyro]

Excellent news

The individual earth rods should do the trick nicely. Might be an idea to check earth bonding to water pipes, etc, whilst you're at it. Tempting as it may be to cross bond them, I think it isn't recommended for some arcane reason (something about a fault in one earth causing problems with adjacent dwellings).

@Gromett I reckon it must run in your blood then, as you are spot on about neutral often being grounded at source. We only have live and neutral supplied by the electricity board at the point of entry to our home in the UK, and earth is split off from neutral at the meter. However, I think it could be dangerous to try to do this with the system at @veevee 's place, best to keep earth completely independent.

On the Brexit issues, we have been in a similar quandary, but news is that properties are selling over here (Portugal) almost the moment they go on the market. Either it is because people are using overseas property as a safe haven for their savings (as opposed to buying to let in the UK) or because they are establishing residency in other EU countries whilst they still can as of right, expat demand is high, despite the low value of the £.

Glad if I have helped in any way. Thanks for the kind offer

 

[Gromett]

Problem solved!

Glad to hear you have resolved it without any frizzy hair or worse

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[pappajohn]

Problem solved!

0v at the wheel/chassis when switched on or off due to the simple fact of having an earth in the supply socket transforming the situation.
An hour ago measured the voltage at the road wheel with the same EHU cable connected to the same shed socket, 69.9v and 14.0v as a residual. Pull EHU cable out of socket and 0v.
Plug into a known earthed socket in the house and both readings are 0v.

I still can't understand how you can have 80vac at the wheel, regardless of an earth or not.
230vac is COMPLETELY insulated from the vehicle chassis ....unless you have a phase/earth fault making the chassis live.
Plugged into the shed would then make the chassis live as there is no earth return to ground...until you touch the metal parts and you become the earth.
If that was the case the RCD in the house consumer unit would trip when you plug in to the 'proved good' house electrics as you still have a phase earth fault....it wouldn't remove the problem.
I'm assuming you do have a modern consumer unit in the house and not an old re-wireable fuse/cartridge type fusebox.

 

[veevee]

I still can't understand how you can have 80vac at the wheel, regardless of an earth or not.
230vac is COMPLETELY insulated from the vehicle chassis ....unless you have a phase/earth fault making the chassis live.
Plugged into the shed would then make the chassis live as there is no earth return to ground...until you touch the metal parts and you become the earth.
If that was the case the RCD in the house consumer unit would trip when you plug in to the 'proved good' house electrics as you still have a phase earth fault....it wouldn't remove the problem.
I'm assuming you do have a modern consumer unit in the house and not an old re-wireable fuse/cartridge type fusebox.

Yes there is a modern consumer unit, it was installed about 2 years ago at the same time as the EDF changed our incoming power from 3 phase to single phase (was previously a small poor hill farm home) , so all was new from outside to the consumer unit. A local electrician connected the existing cables to the new consumer unit waiting for us to upgrade the cottage which we started this year, but Brexit has called a halt for us at the moment.

I don't have your experience but I couldn't understand why the 230vac is not completely insolated from the vehicle, but the sequence and readings really happened as it is written. The RCD's in the new consumer are all Legrand and new with the consumer unit so don't think there is a failing there? but of course sometimes even new parts fail.
If you have any further suggestions I'd appreciate them, failing that I have a good mate who is a serious auto electrician who I would ask to check the MH over when we are back late August.

I wouldn't call the house electrics good, this is a very old house with associated oddities, but I did check the relevant earth cables and they were good. I'm sure you have seen it all before but a few exterior electrical fixes were truly amazing, and looking at the age of some of the units have been working in their original condition for at least 50 years.

Thanks for your input

 

[veevee]

On the Brexit issues, we have been in a similar quandary, but news is that properties are selling over here (Portugal) almost the moment they go on the market. Either it is because people are using overseas property as a safe haven for their savings (as opposed to buying to let in the UK) or because they are establishing residency in other EU countries whilst they still can as of right, expat demand is high, despite the low value of the £.

We aren't panicking but being cautious as we were considering spending 10's of thousands on improvements here starting this summer, but if the 3 Brexitiers make a horlicks of the negotiations then that hard won money may be like water down a drain. So we'll enjoy our time here for the moment and fiddle around the edges of what needs to be done until a clear direction is given and an indication as to what the new rules of the UK outside the EU will look like, plus of course how ex-pats will be regarded by the EU.

There are so many other options in life if this goes t..s up, we would probably go back to full-timing again for that taste of ultimate freedom.

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[pyro]

@pappajohn I think that the voltage being measured at the chassis is induced voltage in the floating (disconnected) earth line in the EHU lead. If you think of the Faraday Rules from school physics, the earth runs parallel to in the EHU lead. Being AC, induced current will flow in the parallel conductor. Bit rusty on the physics, but I think that is how it works. As soon as the earth lead is tied to an actual earth, this low induced (but still sufficient to kill you) voltage simply dissipates.

As to why the fault never tripped the supply RCD (back in the house), the house didn't have an earth, therefore there was no reference point against which earth leakage could be determined

 

[pyro]

@veevee I understand where you're coming from. Whilst I voted to remain in (and would probably do the same again), I'm not convinced Brexit will (if it ever happens, or the EU survives in its present form long enough to make it necessary) make that much difference

Over here (Portugal) everyone is amazed that the UK had the courage to hold a referendum. It wasn't the result I wanted, but aside from a natural apprehension about the short term future, predictable "collywobbles", it doesn't seem to have been as catastrophic as feared. Ironically, the biggest concern over here is the number of incoming French moving to avoid high taxation

 

[veevee]

I guess the only thing we know for certain is nobody has a clue what the next few years will bring, how exciting!

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[tonyidle]

Yes there is a modern consumer unit, it was installed about 2 years ago at the same time as the EDF changed our incoming power from 3 phase to single phase (was previously a small poor hill farm home) , so all was new from outside to the consumer unit. A local electrician connected the existing cables to the new consumer unit waiting for us to upgrade the cottage which we started this year, but Brexit has called a halt for us at the moment.

I don't have your experience but I couldn't understand why the 230vac is not completely insolated from the vehicle, but the sequence and readings really happened as it is written. The RCD's in the new consumer are all Legrand and new with the consumer unit so don't think there is a failing there? but of course sometimes even new parts fail.
If you have any further suggestions I'd appreciate them, failing that I have a good mate who is a serious auto electrician who I would ask to check the MH over when we are back late August.

I wouldn't call the house electrics good, this is a very old house with associated oddities, but I did check the relevant earth cables and they were good. I'm sure you have seen it all before but a few exterior electrical fixes were truly amazing, and looking at the age of some of the units have been working in their original condition for at least 50 years.

Thanks for your input

It's one of the dangers of using a decent meter. Simply connecting one probe to a good earth (or the earth itself!) and connecting the other to any NOT earthed lump of metal will cause the meter to read an AC voltage. The bigger the lump of metal, and the better it's insulated from earth, the larger the reading will be. It's caused by the lump of metal acting as an aerial (in simple terms) and picking up radiation from nearby mains supplies. It won't hurt you because it cannot supply enough current to do so (a bit like the several thousand volts of static when you see a spark). "It's Volts that jolts but (milli)Amps that kill".

 

[pyro]

Whilst it is true that it is a product of both current and voltage that will kill, it is also a fact that any voltage over 50V (which this was), combined with a current of more than 50mA (which we don't know) is defined by the IET as being the threshold of potentially lethal exposure.

A high impedance test meter will often react to RF (radio) or EMI (radiated electrical interference) pickup through its test leads, giving a spurious voltage reading, albeit at an indiscernible current.

However, the problem in this instance was caused not by the short test leads of the meter picking up stray voltage, but by induced voltage in a parallel floating earth, extending over some distance. I would be very hesitant to dismiss the risk to life too casually

 

[mitzimad]

I still can't understand how you can have 80vac at the wheel, regardless of an earth or not.
230vac is COMPLETELY insulated from the vehicle chassis ....unless you have a phase/earth fault making the chassis live.
Plugged into the shed would then make the chassis live as there is no earth return to ground...until you touch the metal parts and you become the earth.
If that was the case the RCD in the house consumer unit would trip when you plug in to the 'proved good' house electrics as you still have a phase earth fault....it wouldn't remove the problem.
I'm assuming you do have a modern consumer unit in the house and not an old re-wireable fuse/cartridge type fusebox.

my 240 incoming is earthed to the chasis which was the way i found most electricians advised when i was building

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[Flamenca]

my 240 incoming is earthed to the chasis which was the way i found most electricians advised when i was building

and if you have an electrical fault the entire chassis can go 'live'

 

[pyro]

and if you have an electrical fault the entire chassis can go 'live'

No, that is precisely what the RCD situated in the incoming mains supply is to protect against.

 

[tonyidle]

Whilst it is true that it is a product of both current and voltage that will kill, it is also a fact that any voltage over 50V (which this was), combined with a current of more than 50mA (which we don't know) is defined by the IET as being the threshold of potentially lethal exposure.

A high impedance test meter will often react to RF (radio) or EMI (radiated electrical interference) pickup through its test leads, giving a spurious voltage reading, albeit at an indiscernible current.

However, the problem in this instance was caused not by the short test leads of the meter picking up stray voltage, but by induced voltage in a parallel floating earth, extending over some distance. I would be very hesitant to dismiss the risk to life too casually

I'm not dismissing the potential danger offered by the situation described - I was simply stating that meter readings should never be taken at face value. Voltage never kills - there has to be a current of sufficient magnitude flowing through the human body for any damage to occur.

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[Flamenca]

No, that is precisely what the RCD situated in the incoming mains supply is to protect against.

No, that is precisely what the RCD situated in the incoming mains supply is to protect against.

and if the RCD is faulty and the chassis is not earthed externally what then?

 

[tonyidle]

and if the RCD is faulty and the chassis is not earthed externally what then?

You will receive a shock if you touch both the van and the ground outside at the same time. The advice Mitzimad was given is correct and guards against the van becoming live if it is in contact with a chafed wire or an appliance mounted to its structure develops a fault that connects a live to its mounting metalwork. RCDs are reliable and should be tested on a regular basis anyway. Ultimate electrical safety is only available to wild campers .

 

[Gromett]

my 240 incoming is earthed to the chasis which was the way i found most electricians advised when i was building

and if you have an electrical fault the entire chassis can go 'live'

No, that is precisely what the RCD situated in the incoming mains supply is to protect against.

This is an interesting debate and really depends on what equipment you have added to your vehicle such as inverters and generators, also how they are wired in and whether you travel to the continent.

I studied this in great depth and went through all the fault conditions I could think of and decided in the end not to bond my incoming earth to the van's chassis as there was fault situations especially on the continent were it was possible for the van to become live. Designing a system to cope with one fault condition is easy, however you really have to plan for 2 simultaneous fault conditions.

On my system I ended up isolating all the 240v electrics fully, running all cables in plastic trunking/conduit so that there was no way of 240v reaching the chassis at all even in extreme fault conditions. I also selected my appliances that were all plastic with no metal surfaces that could come in contact with the mains under a fault. Plastic toasters etc etc instead of metal ones. I expect at some point I will connect my van to a supply with a duff earth and want my van to be safe when this happens.

If you have your van chassis bonded to earth and you plug into a supply with no earth, then you are in a situation where one additional fault could leave you with a live chassis.

There were lots of debates at the time about earth rods when using generators etc...

The problems with asking most electricians is that they don't have experience of mobile usage and very few if any have experience of continental electrical systems. They tend to give the standard practice as advise without having thought through the potential fault conditions.

These are just my opinions based on research 6 years ago on top of my original training. Your level of risk, usage and configuration may vary though and this should not be considered as advice on what to do on your installation!!!

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[pyro]

@tonyidle Agreed. We rely on RCDs in domestic environments, and they are both reliable and have saved countless lives since they were first introduced.

An electrical safety test should form part of any annual habitation check, and RCD's all feature a means of self testing

@Gromett In the majority of cases, people don't keep to double insulated appliances, thus for them the risks remain high, and on balance it is probably better for them to have the chassis earth bonded.

I presume from what you say that you still maintain earth continuity to the RCD, and from there, through to all the van's 230V outlets? In which case, you still have the protection of the RCD in series with the supply

Certainly there is provision within IET Regulation 721.411.3.1.2 which requires structural metallic parts that are accessible from within any caravan/motorhome to be connected through main protective bonding conductors to the main earthing terminal within the vehicle. Presumably that means the cross bonding of chassis, steel sinks, taps, handles, etc. http://electrical.theiet.org/wiring-matters/61/caravans/index.cfm

The whole issue reinforces the sense in always carrying with you a "Martindale" type tester, where the presence of earth and correct L-N polarity can be easily identified. If nothing else, you know that when you switch something off, you have interrupted the live supply.

 

[Gromett]

I presume from what you say that you still maintain earth continuity to the RCD, and from there, through to all the van's 230V outlets? In which case, you still have the protection of the RCD

That is correct. But if there is an earth fault on the supply then the RCD would not trip as the current going to the earth side has no where to go.

PS: You did make me think, if the current flows through the body of course the RCD would trip,....