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

Reply to
petek
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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

Reply to
D.M. Procida

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.

Reply to
Dave Plowman (News)

=A0 London SW

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

Reply to
petek

It needs checking out, as others have said.

However, my guess is that you'd somehow managed to aquire an electrostatic charge, which discharged - giving you a tingle - when you touched the radiator and switch. The same thing would probably have happened had you touched only one of them. In this cold weather, the humidity is very low, and it's easy to build up quite a charge - especially if your carpets and/or clothes contain nylon.

Reply to
Roger Mills

= snipped-for-privacy@davenoise.co.uk =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD L= ondon SW

=EF=BF=BD =EF=BF=BD To e-mail, change noise into sound.

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

Reply to
meow2222

You could get a fairly unpleasant shock just from capacitive coupling between the live and floating earth conductors without any direct connection between them. However, if you were using your AVO (I am assuming a model 8) on the 250Vac range, it was drawing nearly 1mA while causing the supply voltage to be attenuated by perhaps 10V to

20V.

Assuming that the leakage impedance is constant, this implies a potential leakage current of perhaps 5 to 10 mA into a low impedance which is a lot for capacitive coupling in your lighting circuit.

Your whole house might have a floating earth connection, in which case you felt the combined leakage currents of whatever appliances were switched on.

If you repeat your measurement on the 250V and 1000V ac ranges in quick succession and also measure the mains voltage the leakage current can be calculated much more accurately. (Don't be tempted to use a current range on the AVO - you risk destroying it and possibly hurting yourself.)

Check that there is proper cross bonding between gas and water pipes and the main electrical supply earth as a matter of urgency. The leakage current could become a lot higher if an electric oven or immersion heater is switched on.

John

Reply to
jrwalliker

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

Reply to
petek

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

Reply to
D.M. Procida

You have indeed.

Only a guess - do the other checks first.

Have you got something you know to be earthed - perhaps a metal kettle etc? Use that to measure to - it only needs to be plugged in, not switched on.

The first step (after doing the tests) is to examine the earth bonding where the services enter the house. If it's not present or faulty this should be seen to before anything else.

Reply to
Dave Plowman (News)

He was seeing 230V between the metal clad lightswitch and the radiator on a 20,000 ohms per volt meter. That's_ not_static

Reply to
Graham.

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.

Reply to
Dave Plowman (News)

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

Reply to
petek

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.

Reply to
GMM

In the interim, I would replace the metal light switch with a plastic one, until you have sorted it all out properly!

Toby...

Reply to
Toby

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

Reply to
Dave Liquorice

It's the potential between live and an earth. Pretty much what one would expect

Reply to
Alang

on 04/01/2009, petek supposed :

Your reading with the meter are correct, but that is not the way to be certain it is properly earthed. Assumming everything is correct with the switch, the other possibility (unlikely) is that the radiator became briefly live.

Sometimes a nerve in your body catches and it can certainly seem like a large jolt.

Reply to
Harry Bloomfield

In message , "Dave Plowman (News)" writes

Should it? Didn't we 'harmonise' with Yoorope on 230V a few years back or have I mis remembered that?

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Reply to
Clint Sharp

I've never understood why anyone would want bare metal around a switch.

Reply to
Matty F

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