Replacing switch...Tingle. Ouch! Power definately off.

[nv_london]

Dear all,

I’ve just moved in to a new place and noticed that the neon switch controlling the water heater was cracked and broken, I therefore decided to replace it. I went to a DIY store and bought an identical replacement. After turning off all the power to the house (the neon light at the front of the switch no longer came on and all other electrical devices weren’t working) I took off the faceplate and started unscrewing the nuts holding the 4 wires in place (one blue, one red, one brown, one balck – the earth wasn’t connected to anything, it was just lying in the back box, but not screwed in) – at some stage I got a tingle / shock from the wires….I’m not sure which one and I’m not sure why.

After looking up a number of different topics in this forum, I read that it could have been static from walking across the carpet, however, I’m thinking that this isn’t the case as when I place my voltmeter near the wires it still registers to a small extent (nowhere near the way it registers when everything is hooked up and the power switched on, but never the less, it does register something). I’ve also noticed that there are special pole switches for water heaters (rated at 20 A I think) (the original one wasn’t – but I’ll now get another suitable replacement). Anyway, I was just wondering if anybody had any ideas as to why there still seems to be some amount of current present and if it were possible to discharge this so that I could replace the switch with a more appropriate one without being ‘shocked’!

(I don’t currently have a multimeter, but would be willing to buy one if it were needed).

Thanks for any suggestions with this DIY project.

 

[Chri5]

Please confirm the blue and brown were the cores of the cable flex to the water heater and that the black and red were the supply cables.

Is the water heater purely for manual topping up or does it intergrate in to the central heating system, and controlled by timers ?

 

[nv_london]

Dear Chri5,

'Please confirm the blue and brown were the cores of the cable flex to the water heater and that the black and red were the supply cables.' - That's correct.

With regards to the water heater, it is indeed intergrated in to the central heating system, and is controlled by timers.

(I knew there were inportant bits I forgot to mention!)

 

[Space cat]

when I place my voltmeter near the wires it still registers to a small extent

What do you mean by (a) "near the wires" and (b) "a small extent"?

It's normal for a voltmeter to read some tens of millivolts when placed IN CONTACT with isolated wiring. That's because the wiring is an aerial and it's picking up all sorts of noise. If you get tens of volts, something is going on. Do you have a high-powered radio/TV transmitter nearby?

 

[JohnD]

it might be you have a voltage between the earth wire (and/or Neutral) in the electrical circuit, and the metal water pipes. To prevent this, (in most cases) you are required to Supplementary-bond all the metal pipes that enter the bathroom, to the earthwire of all the electrical circuits that enter the bathroom.

Additionally, the water-main and gas-main entering the house should be bonded to the main electrical earth at the Consumer Unit (fusebox) or by the meter. This deals with any voltages coming in from outside your home (which there can be).

If you live in a flat, especially an old one or a converted larger house, the cables and pipes may be connected in another home and voltage may come from a fault in there. This is particularly common in watery appliances like immersion heaters.

Have a look for green-and-yellow striped cables in the bathroom and the mains,and observe (a) if there are any (b) how big they look (c) what they are connected to. Post some pics if you can.

We have instructions on how to do it. The materials are quite cheap.

It is a fairly easy DIY job to fit it, or you can pay a SUITABLY QUALIFIED electrician, who can carry out some tests that are beyond most DIYers or general handymen. Most of the cost is in the time it takes to crawl about the floor or in dusty airing cupboards tacking wires to walls and tightening screws while lying on your back in the dark.

I recommend you buy a simple Multimeter anyway to measure the voltage. It will cost less than £10

 

[nv_london]

a) 'near the wires' means that the voltmeter wasn't picking up any signal outside the socket (which it usually does, when the power is on and the socket is switched on) but rather, that it was only picking up a signal when the face plate was removed, and when I held it next to the wires now on show. (It wasn't registering any signal when I placed it in direct contact with the wires, but rather when I hovered it over the wires generally).
b) 'small extent' means, that unlike when everything is switched on and the voltmeter lights up brightly and beeps loudly when it's placed near the socket on the outside, after I switch everything off and open up the socket, I now have to hold the voltmeter quite close to the exposed wires to register any type of signal whatsoever.

It also states on the voltmeter that it can detect above 50 mV, I'm therefore assuming that I'm around this range (but I know that I would need a multimeter to be more accurate).

By the way, i don't have any transmitters near by.

 

[nv_london]

I do indeed live in the upstairs floor of a very old flat - but I did switch off downstairs' electric as well (just in case), but the same thing still happened. (I doubt it could be from next door's wiring, but who knows!).

I'll have a look for the green and yellow wires, but at the moment, it sounds like my best bet is to get somebody who knows what they're doing.

 

[JohnD]

if you're going to pay someone, ask them when phoning if they are a member of a self-certification scheme, and which one. A qualified professional will not mind you asking.

//search.diynot.com/forum_sear...mit=drop&since=90&author=&search=Search+Forum

 

[ban-all-sheds]

It also states on the voltmeter that it can detect above 50 mV, I'm therefore assuming that I'm around this range (but I know that I would need a multimeter to be more accurate).

It's not a voltmeter....

 

[nv_london]

Sorry! I meant, voltage detection pen.

 

[Steve]

Sorry! I meant, voltage detection pen.

Oh dear. Go and buy a multimeter.

 

[nv_london]

Will that fix the problem Steve?! Oh dear, I don't think it will!

Thanks for your helpful suggestions JohnD.

 

[electronicsuk]

Sorry! I meant, voltage detection pen.

Oh dear. Go and buy a multimeter.

Will that fix the problem Steve?! Oh dear, I don't think it will!

Actually, it will help a great deal. A voltage detection pen does not allow you to measure the potential difference (voltage) between two points, nor does it give any indication of the voltages present.

A multimeter would allow you to see what the voltage is between live and neutral, live and earth, neutral and earth and find out how you managed to get a shock. What's more, you will know how high a voltage (if any) you're dealing with.

Do not underestimate the importance of having the correct tools.

 

[nv_london]

Thank you very much Matthew.

I'm not underestimating that wahtsoever.

I'm just slightly miffed at a reply a long the lines of 'Oh dear. Go and buy a multimeter'.....?!? And then what.......?! Go and put your feet up and have a cuppa?!.....Go to the pub?!?! Go and do something constructive with it?! Sometimes I think people just write something/anything for the sake of increasing their posts but don't actually answer any questions or give any helpful suggestions. - Then again, if you've got nothing else better to do with your time, then so be it and carry on.

But if you finish it off with the suggestions you gave i.e. where to measure, what to measure and what you're looking for, then great. _ I will go and get one and do as you say.

I really appreciate your helpful suggestions.

Thanks a lot.

 

[JohnD]

that told you steve