Shock from lightswitch/radiator

I was leaving our bedroom the other day and I was turning out the light when I put my other hand on the CH radiator just to check if it was warm. Big shock and tingling fingers on both hands! The lightswitch is a stainless steel cover plate with plastic rocker switches.
I have removed the switch from the wall to check the connections and all looks OK, no bare wires touching anything else, and the earth wire in the switch cable is connected to the terminal on the cover plate. I have an old AVOmeter passed down to me by my father-in-law and a rudimentary knowledge of how to use it. It is showing approx 230 volts between one side of the switch terminal and the earth terminal, which I think is to be expected.
I have gingerly tried touching the rad and the switch simultaneously again, but I don't get a shock now.
Have I got a problem? If so, is there anything else I can do to trace the fault and hopefully correct it?
TIA Pete
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In the teaching profession, you'd be what we'd call a "slow learner".

One problem is that you're prepared to risk current from the mains across your heart.
I'd suggest that you forbid anyone else in the house to touch either the radiator or the lightswitch, avoid touching other radiators and metal plumbing, and other steel switch cover plates if you can, and call an electrician first thing tomorrow morning.
There could be any number of faults in the system (often receiving a shock is a sign that there are indeed several faults). Consequences like elctric shocks might only occur under a particular set of circumstances, and some of these might not be at all obvious.
Daniele
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In article

Should actually be 240v.

Use the AVO to measure between the switch plate and a good connection on the rad. You should get effectively a zero reading. Make sure it's set to AC volts. Just for information I've done the same here and get a reading - using a high quality DVM - of 0.0027V.
Now check between the switch plate and the ring main earth. If you have plastic sockets one of the screws should be good enough. Again, the reading should be zero.
By this you can identify if there's a problem with that switch circuit or the bonding elsewhere. My guess is that the ECC in the switch wire isn't actually connected to anything at the other end.
--
*Succeed, in spite of management *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Thanks Dave, thats been helpful so far.
I have scratched away a bit of paint on the rad and measured between there and the switchplate. The AVO shows about 225v (I take your point re 240v but maybe there's some local variation in mains voltage today). So it looks indeed as though I have a fault somewhere. Thinking about it, this would support your guess that the earth wire is not connected at the other end.
I haven't checked between the switchplate and ring main earth at this stage because that would mean me having to rig up some temporary extensions to the AVO leads. The nearest socket is 3-4 mtrs away.
I suppose my next step is to trace the wiring in the loft and find out if the earth conductor from the switch is connected to what and where. Also while I am up there to check if a live conductor is actually touching something it shouldn't. Any other ideas?
Pete
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petek wrote:

your next step is to test from rad to a reliable earth, and from light switch to reliable earth, to find out which one's live. Then report back, if still alive.
NT
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On 4 Jan, 17:13, snipped-for-privacy@care2.com wrote:

OK, I've not been in the loft yet, but have done some more testing as NT suggested and I'm still alive, but getting more worried!
There's no voltage showing between the rad and nearby ringmain earth (I assume a "reliable earth"). The resistance between the rad and ring main earth is only 1 or 2 ohms, so this suggests the rad is earthed OK, I think.
There's a voltage of 225v approx showing between switchplate and ringmain earth, which is in line with previous tests i.e. 225v between switchplate and rad, and very little resistance between rad and ringmain earth. There is a high resistance (i.e. no needle movement on the AVO) between rad and switchplate
So, this looks to me as though the switchplate is indeed live, and the earth conductor in the switch cable is not connected at the other end (as Dave guessed). Up to the loft I go .........
Pete
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wrote:

Ouch - 225VAC across the poor avo's resistance range...
--
Geo

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I'm somewhat surprised that having reported receiving a "big shock" from alight switch and radiator, no-one else is advising more caution to someone who doesn't seem to have very much expertise.
Let's assume that it wasn't just a big electrostatic discharge (most people can tell the difference). The most likely cause is an earth that has gone live, and the switch plate with it. What else should be earthed but might now be live?
I've discovered, on more than one occasion, DIY electrical work that was ready to kill, including the (supposed) earth in lighting circuits that was in fact switched live.

That would still require a second fault, to give someone a big shock just by touching the switch plate. The earth circuit is to offer protection against such faults. So Pete's dealing with a circuit with a fault, and faulty protection.
Daniele
Daniele
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In article

I've seen that done by pros. Big reputable firm too.

Capacitive coupling can easily cause a tingle. The earth wire not actually connected can give this effect. The OP has already proved it's not connected so is halfway there to sorting it. However, it might well be a bigger job than he imagines - there might not be any ECC connection on the lighting circuits, and never has been.
--
*Change is inevitable, except from a vending machine.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 4 Jan, 17:43, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

OK Daniele, thanks for your concerns which are much appreciated. Just to set the record straight in terms of my expertise. I have a BSc Hons in Mechanical Engineering (which included some electrical/electronic theory) albeit 40 years ago, and reasonable experience of simple DIY electrics but I admit I am not up to scratch with capacitive coupling and leakage impedance although the terms are a bit familiar from 40 years ago.
I have experienced static shocks many times previously and this felt more like a mains shock (which I have also experienced in the past!)
To reply to John, my AVO is a Model 8 and I have been using the 300Vac range (there isn't a 250Vac range).
My excursion up to the loft has revealed nothing untoward visually in terms of electrical connections, i.e. no bare wires or loose connections, but there may be a problem with the connection of the switch cable earth conductor at the ceiling rose. I can't check this properly as it will mean moving the bed to get at it and I don't want to start doing this on a Sunday evening. I may have a go tomorrow. If indeed this is faulty then it would support the theory that the stainless steel switchplate is not effectively earthed.
There also appears to be a break in the lighting ring earth between this bedroom light and the next light in the circuit, where a spur has been taken off using a junction box and the earth wire not continued IYSWIM.
Which leaves me with the conclusion that the earth circuit is not 100%, and that there is a fault somewhere that is making the switchplate live. But how to trace this fault........?
Think it's time to bite the bullet, get a leccy in and take out a second mortgage to pay him!
Pete
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I could easily be wrong (and I'm sure someone will correct me if I am), but it seems to me that 230V from the switch plate to a good earth indicates not only that the cpc in the lighting circuit is not connected to a good earth but also that it's connected to a live somewhere around the place. So either it's wrongly wired (into a live rather than an earth connection) somewhere or that something has shorted to the cpc and failed to blow the fuse/trip the mcb as a result of the cpc not being connected to earth. If I'm right, it might be that the whole of that lighting circuit shows similar properties, which might be pretty/very dangerous to anyone in the house. I would carefully test the voltage to earth of another switch on the circuit to check this.
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wrote:

In the interim, I would replace the metal light switch with a plastic one, until you have sorted it all out properly!
Toby...
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I've never understood why anyone would want bare metal around a switch.
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On Sun, 4 Jan 2009 11:00:29 -0800 (PST), petek wrote:

Lighting circuits are generally not rings just a series connection. Looks like you have found the problem...
--
Cheers
Dave.




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petek wrote:

Its possible that this is the only fault - that could leave a large section of the earth wiring in the circuit floating, and hence it probably would tend to acquire a mains potential due to proximity to other live wires. If this were the case you ought not be able to get a dangerous shock from it.

If you turn the light switch on (such that both wires in it are now live) and measure the voltage between one of them and the earth, what reading do you get then? Only if it is 0V (or close) would that suggest a physical low resistance fault between live and earth).
The other test to do would be to disconnect the circuit at the consumer unit, and measure the resistance between live and earth of the cable feeding the circuit. You should see an open circuit.
--
Cheers,

John.

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Personally I would turn everything off and conduct a visual examination by following the earth wire back.
--
Michael Chare


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petek wrote:

What no-one's yet mentioned is that if the earth fault isn't local to the switch only, reconnecting an earth wire could result in lots of other stuff in the house also becoming live. And if the earth fault is unfortunately situationed, you or your family may be frying tonight in the shower.
Really your last sentence is the best advice you can take. Despite your protestations of knowledge, some of the things you've said are plain scary, and some of the things proposed just dangerous.
NT
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It's all gone silent since Sunday night. I hope that the first visit Pete had on Monday morning was the electrician, and not the paramedics.
Daniele
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On 6 Jan, 13:13, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

Still here, alive and kicking! Nice to know that you are thinking of me!
After a bit more testing and much thought on my part, the aforementioned leccy turned up on Monday afternoon. He repeated many of the tests I had done with my AVO, but with more modern electronic/ digital test kit. After some more thought, the conclusion was that there is a probable live to earth fault in the lighting circuit (not sure where yet) and that there is a probable break in the earth line somewhere between the fault and the CU or even that it is not connected at all, which is why the fuse has not blown.
We then took the cover off the CU, and guess what ............ although we could count 8 live (red) wires and 8 neg (black) wires - cooker, 2 x power rings, 2 x lights and immersion heater - there were only 7 earth (yel/green) wires visible! . This probably goes back to the time when we had the kitchen re-fitted about 15 years ago, and the guy who did it had to move the CU about 1/2 - 1 mtr along the wall behind the cupboards. IIRC, he was a joiner by trade and did it himself - who said Part P was rubbish?
You will have guessed that the CU is fairly old (30 yrs), and has wired fuses. So, the first job is to replace the CU with a new mcb CU and at the same time see if the missing earth wire can be traced and connected properly. Estimate for this part of the job is 210 which sounds reasonable I suppose. After this we can set about tracing the fault by isolating each bit of the lighting circuit in turn. He can't give me a price for this obviously as we don't know how long it will take, could find it straight away or sod's law says it will be in the last bit that is tested.
He's coming round later this week to do it, but meanwhile he has replaced the stainless steel switch with a plastic one.
Just a couple of Part P type questions -
His business card says "JIB Approved Electrician". Is this OK in Part P terms?
After he has finished, what documentation if any should I expect? Test Cert perhaps?
Regards and thanks again to all
Peter
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petek coughed up some electrons that declared:

http://www.jib.org.uk/gdappelec.htm
JIB is an more industrial thing.
It almost certainly indicates his competence to a good standard, but I don't think it implies directly that he's set up for Part P self notifications.
Ask if he's registered to self certify for Part P and with whom. Assuming you care!?

You should expect (and ask for in advance) a EIC (Electrical Installation Certificate) and some sort of evidence of Part P notification (never seen one, can't tell you what this looks like).

Cheers
Tim
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