# One For All the Electrical Gurus Out There



## Paulway (May 9, 2005)

Hi All,

Just had a new and 'interesting' experience that I hope may make a change from battery charging and the like!
I was crawling under the van yesterday inspecting mishaps abroad (another story) when suddenly to my temple there was a spark bright blue flash and the definate feel of an electric shock, not a static one for sure, as I was in close proximity to a chassis member. I will add that the back of my overalls were wet and I was rather covered in perspiration at the time.
I was still in one piece so to speak so I carefully, not carefully enough, eased my way out from under the van and in doing so my arm contacted the handbrake cable from where i felt a mains 'vibration' through my overalls and jumper. I then contacted the exhaust with my hand, not purposely, and again the definate feel of mains AC but now realising that this could not possibly be full mains voltage, or could it.
Today I have been doing some testing and find that there is an AC voltage of around 28 volts on all metal parts of the chassis and engine.
Now I am in the processof trying to find the problem, is there one(?), and have tested polarity and earth faults on circuits using a Martindale tester, all show as good and am slowly working around isolating as I go but as yet cannot determine where the 'leak' is.
As I have just stopped for a break I thought I would share this one with you to see if it is unusual, (this is the first time I have crawled about under the van with it connected) why does the RCD not drop, it is working perfectly on the 'Test' function.

Cheers 'A bright spark' Paul


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## Scotjimland (May 23, 2005)

Hi Paul 

an ' electrifrying' experience no doubt .. 8O 

I would check the hook up cable for a loose or broken earth wire, the ELCB isn't tripping suggests that there is no earth connection to the van.. 
The test switch checks the unit not the integrity of the earth path. 

Ill sit back now and let an expert shoot me down .. 


Jim


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## Paulway (May 9, 2005)

Hi ScotJimland

Thanks for the reply, it truly was, just glad it wasn't full voltage!!
Yes that was what I thought to but both the Martingdale test on the sockets says its ok and using a digital multimeter there is well under 1ohm resistance to earth down the earth lead!!
Hence my posting because I am starting to think what the heck is going on here!!


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## spykal (May 9, 2005)

Hi Paul

first suspect has to be the power unit but no doubt that is where you started.

So these are stabs in the dark:

1. Did you have the immersion heater switched on....leakage is possible from a faulty element even if under normal use it heats the water.

2. Did you have the TV on or on standby...mains TVs are notorious for faults that can lead to the coax outer becoming live.

3. Maybe it is not the van wiring but the house wiring :roll: 

if I come up with any more I will post them :lol: 

mike


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## Paulway (May 9, 2005)

Hello Spykal

After testing leads I disconnected the Zig power unit with no effect. The immersion heater has the fuse pulled, no TV connected. I am about to test the house wiring as a precaution but that also has an RCD and that has not tripped either.
What I cannot get my head round at the moment is if the earth connection is correct how can I be getting voltage on the chassis when measured to the ground, surely it should be under the same potential!

Thanks for any thoughts and advice Paul


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## Scotjimland (May 23, 2005)

Paulway said:


> What I cannot get my head round at the moment is if the earth connection is correct how can I be getting voltage on the chassis when measured to the ground, surely it should be under the same potential!


This is excatly correct Paul, .. there must be a poor eath connection somewhere. 
Either in the lead or in the house ..

This reminds me of some years ago in France we were getting shocks from the van when we stepped out and touched 'earth' . I suspected a bad site earth and as a remedy drove a steel peg into the ground and connected it to the van chassis. No more shocks .. 
I reported to the site manager but he just shrugged.. telle est la vie lol

Jim


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## 92046 (May 1, 2005)

*Earth*

Hi Paul

This is a nice one to get the grey matter working

The house may be well bonded, all the earths bonded to one point ?

Is that point well bonded to the general earth outside the house, or is it floating above the general earth, by a few volts ?

Using a digital multimeter may pick up a floating earth, where a Avometer or heavy voltmeter may pull this down to the same potential,

can you measure a voltage from the house earth, to the ground in the area where you ""felt"" the voltage ?

Have fun & wear rubber gloves 8O


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## Scotjimland (May 23, 2005)

*Re: Earth*



Cowly said:


> Have fun & wear rubber gloves 8O


And rubber underpants .. :lol: :lol: :lol: :lol:

Just a thought, have you had a look inside the van hook up socket.. ? With all the recent rain it might be damp inside ..


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## spykal (May 9, 2005)

Hi

more thoughts:

1. sorting out the earth will solve the shock problem but not find the leakage

2. have you any water / moisture ingress into the hook up point.

3. spiders nests in any junction boxes, connection blocks(not a joke)

Mike


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## 96560 (Oct 22, 2005)

The "spark" and "shock" could be different problems perhaps? Digital meters don't necessarily give the best result for some voltage measurements (input impedance too high). 28 volts could just be "noise" (metal parts of van acting as a large receiving aerial). 
You don't say what the 28 volts was measured with respect to. "Earth", ie, local ground) or the earth cable? 
There are different types of earthing systems used in houses (TN, TN-C, TN-S, TN-C-S, TT etc). Ask your supplier what yours is if not clear from your incoming cable connections. Some have the neutral connected to local earth, some have this link back at sub-station and others have local separate earth via local earth rod. These different arrangements can confuse the picture too. There are also issues of balancing (3 phases plus neutral from sub-station and phases shared around houses/streets to try to get similar loads on each). A net effect of this is to raise the neutral voltage with respect to earth. Not familiar with the "Martingdale" tester, but does it check your polarity? Easy way to check polarity is voltage measurement phase to earth (around 230 volts) and neutral to earth (much lower). Be sure that your polarity is correct, in the house and in the van. Once these issues are clear, continue progressively checking along the circuits as you seem to be doing. The "overcome" the digital meter high input impedance issue, a parallel load could be applied between chassis and earth reference point (effectively across the meter, but only for this test, not on known live circuits). Parallel load could be a resistor (from local Maplin or electronics store perhaps) of say 100 k ohms. Also inspect the "spark" area (with mains disconnected from van) and see if there is a van 12v circuit fault type explanation for it (as if mains derived, a "spark" should have tripped a correctly connected RCD).


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## DABurleigh (May 9, 2005)

Generally speaking I find earth & leakage path problems as much black magic as radio frequency circuit design at microwave and above. But if I were a betting man I'd say Mike was right with his first number 3:

3. Maybe it is not the van wiring but the house wiring 

Dave


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## 89122 (May 14, 2005)

If you have a generator try it with that and see if it is the same.
Eddie


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## Paulway (May 9, 2005)

Hello Everyone

Well, I am still unsure about some aspects of this but I now know the cause!!

Checked out the house wiring and main and supplementary earthing all correct, have relied on the Martingdale for several of the tests but also using the multimeter at the fuse box, (sorry JSW the Martingale tester is a propriatry reverse polarity, earth fault and neutral fault tester bit like saying 'Hoover' for vacuum cleaner I suppose). The 28volts was measured to a metal stake in the ground by the way.
Several of you were on the right lines because it was wetness causing the problem.
As I said I was inspecting under the van after our near disasterous trip to France this year, where we had a tyre explode at 70mph on the M20 whilst going to Dover for the ferry. The tyre became a 70 mph flail that caused an imense amount of damage to the underside of the van. The sandwich constructed floor was obliterated approx 6 x 12inches through to the inner wood, GRP skirts smashed along bottom and electric step damaged so it did not work. Thats what I had seen to be the problems.
What I had not seen is behind the wheel arch, hidden behind the mudflap also, the main electrical wiring passes from the nearside of the van where the inlet and battery compartment is , past the wheel arch to the far side of the van where the RCD is installed in the wardrobe base. The flailing tyre had destroyed the convoluted plastic conduit that the wiring was protected by and partially cut into the main wire, water has entered the outer sheathing and there is damage to the inner sheathing thus giving a path to earth.
The reason that the van RCD did not operate is because the fault is on the inlet side however I am at a loss to explain why the house RCD did not operate, it is quite sensative and has been known to shut off during thunderstorms.
I am now renewing the supply cable and I am making a metal cover plate to go behind the wheel arch to protect the wiring, some of the low voltage cabling crosses here to in a seperate conduit, so that should there be another blow out at least the wiring will be protected.
After seeing this I would advise everyone to check whether they have wiring in the vicinity of the wheel arches and if they do ensure the protection given to it is sufficient to defeat the flailing metal band of a burst tyre.

Thanks everyone for your help.


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## Scotjimland (May 23, 2005)

All's well that ends well.. glad you found the problem and getting it sorted..  


Jim


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## spykal (May 9, 2005)

Hi paul

Thats good news ...you will now be able to sleep tonight, but if f you were a cat I would say that you now have only eight lives left :lol: 

Mike


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## 91929 (May 1, 2005)

Was just going to say Jin scot lad was correct in whatever he said (lost it in reading your last letter)

Reason why the house RCD didnt trip was because there was no earth curerent flow down the hook up 

Although the wire was cut through to the Cunductor & you got a shock to earth through your wet overalls 
That does not mean that there was a significant current flow (if any) down the earch wire to the house RCD enough to operate the trip

The leakage to earth was through you or through your metal spike

You could make another test to see if the van chasis etc is connected to the earth of the mains connection - if not that could be a reason why the home RCD did not trip

I am not sufficiently up with the regulations re connection of mains to Caravans and motorhomes as they are not covered by those that cover industrial and domestic installations

i was originally thinking in terms of a fault in the battery chargeing department


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## Brambles (May 12, 2005)

"That does not mean that there was a significant current flow (if any) down the earch wire to the house RCD enough to operate the trip".

PnP, I think you and a few others misunderstand how an RCB works. It does not sense the current down the earth wire. It works by sensing a difference between the Live and Neutral. The imbalance being what could be going down the house earth but also could be any other path to earth.

I think it is most likely the leakage was just not enough to trip the RCB. A test with the meter between the earth wire of your extension lead to the ground stake will show up any fault with the house Earth but do also check for 230 volts between the Earth wire and Live as it could actually be open circuit.
Depending on the earth arrangement in the house there may actually be a few volts showing on the Earth wire to ground or Neutral.
Jon.


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## spykal (May 9, 2005)

Brambles said:


> I think you and a few others misunderstand how an RCB works. It does not sense the current down the earth wire. It works by sensing a difference between the Live and Neutral. The imbalance being what could be going down the house earth but also could be any other path to earth.


Quite right Jon but only for most RCBs. This is where offering online advice can be difficult. You would need to see or know what type of device was protecting pauls house to be certain that what you have said is correct....I know we get told off for rabbiting on but to be accurate you must not forget that there are several types of RCDs (some are known as Earth Leakage Circuit Breakers) which are primarily designed to protect against electrocution.

RCDs are nowadays mostly current operated, but there is also the older voltage operated Earth Leakage Circuit Breaker (ELCB). Voltage operated devices have the disadvantage that as they measure earth leakage directly, they can only detect leakage to the earth circuit that passes through them. Thus, they will not detect current passing through the body to the ground when using equipment outdoors.

mike


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## Brambles (May 12, 2005)

Thanks Spykal for mention ELCBs (Earth leakage circuit breakers). I suppose I should have mentioned then as well. If anyone does have an old ELCB they should really consider replacing it with an RCB or RCD ( Residual current Breaker or Residual Current device). So confusing with abbreviations, so off to play a VCR in my DVD!!! )


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## Paulway (May 9, 2005)

Hi Spykal and Brambles

Yes this is my concern now as the device is indeed an RCD and the unbalanced line and neutral should, by my understanding and apparently yours, have tripped but it didn't. If you press the test button it trips and it has tripped in the past so giving no indication of a problem, in fact an old Flymo lawnmower makes it trip as soon as the mowers o/heat protection cuts it off, so I have until now had no reason to doubt its operation!
This experience has now got me wondering and I will probably change the RCD to be on the safe side. But to me it still is a timely reminder to not rely on anything to save your life but removing any possible dangers before you start. Having said that, had I not gone under the van without disconnecting the mains first, I would never have known I had a problem, so I am not sure whether it is good or bad as maybe something more serious on a site might have happened, I will never know.
One thing, I have added a chassis to the ground test to my list of periodic checks that I do and will check it for definate annually when I do a full habitation overhaul, cannot remember the dealer doing it as part of the habitation check when it was under warranty (I did used to wait and watch while the inspection was carried out).


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## Brambles (May 12, 2005)

Paulway,
I think you may have highlighted a potential hazard on your make/model of Motorhhome. If tyre tread/bands lashing round could damage the cable I would assume other objects thrown up by a tyre could damage the power cable before it is connected to the RCD and short the supply to the chassis. Maybe something that should be taken up with manufactures as a safety issue. I would expect any Motorhome to be wired with the mains inlet as close to the protection devices as possible and suitable protection afforded to the cable from inlet to safety device.
Jon.


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## 88966 (May 11, 2005)

Hi Paul and Others,

I am glad that you have sorted your problem. Just for interest and to show how these strange things can happen I will recount something that happened to me a couple of years ago.

I live in a little hamlet of 6 houses all off 1 mains transformer. One day my neighbour came over quite concerned and said she was getting shocks every time she touched the taps at her kitchen sink, did we have any problem ?

I got out a meter and found that we had about 30 volts on the earth bonded metal work compared to a real earth.
I called out the local elec. distribution Co., but before they came I had a suspicion ??

I had a rather long temporary lead up to a tractor shed and someone had damaged it (driven over it) so that it was shorting internally - but had not blown the supply fuse. I disconnected it and the 'fault' was cleared.

When the supply people came they couldn't find a fault and said it was probably an intermittent earth fault - and they are the most difficult to find !!!!

They 'explained' that with the system they now use the neutral is used as the earth and therefore it is possible for it to float above true earth by some small amount.

This seems to relate very closely to Paul's story. The voltage of about 30 volts I know I cannot feel normally but with wet hands ( my neighbour) and lying in dampness (Paul) reduces the surface resistance of the body and makes it more sensitive.

I hope this was of interest.


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## DABurleigh (May 9, 2005)

Paul,

From a few instances over the years I still associate a voltage of around 28V ac with house mains wiring/ earth issues. Maybe I haven't digested all in this thread, but did you conclude the 28V was due to resistive losses from a full 230V due to the damage, or potentially (ha ha) something further back up the chain?

Dave


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## Paulway (May 9, 2005)

Hi Brambles BillD and others,

Brambles I am considering, no will be, moving the van RCD to the nearside next to the inlet and feeding new wiring to the supplies on the other side of the van, that way all below van wiring will be covered by the RCD, got to be a safer bet.
Tha is an interesting tale Bill and does seem to reflect my experience, so from what you are saying it does not always mean that an RCD will trip if the voltage is very low? That seems to fly in the face of what the benifit of an RCD is supposed to give, but it would be good to know that my house one isn't faulty, I'll probably still change it though!!


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## 88966 (May 11, 2005)

I think it confirms that everything about electrics is not always black and white (or red and black or blue and brown).

The fact that my cable was severely blackened inside and was obviously tracking across but not sufficent to blow a15 amp fuse and the lengths of cable involved must have had a combined effect to raise the neutral voltage.


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## oldun (Nov 10, 2005)

In a motorhome the mains circuits are protected by an earth cable. Is this cable bonded to the chassis?

Another oddity when on a mains hook-up we have an earth cable for protection. When using a generator there is no earth protection.


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## Paulway (May 9, 2005)

Hi dj
yes in my case the earth is bonded to the chassis, which is why I couldn't get my head round what was happening. 
My understanding with generators is that you should in fact put an earth rod into the ground when you are using it to give earth protection. If that is not correct, as I do not use one anyway I am only repeating what I have read elsewhere, perhaps someone could correct me!!


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