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

[Steve]

<cowers in corner and hides>

 

[Chri5]

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

I'm not super smart with CH wiring centres, I'm awaiting the Honeywell road trip / £30 course to go local.

So if the water heater is part of the CH could there be voltage via the wiring centre, boiler live, prog unit etc ???

Or are we (as in the other poster responders) happy that the immersion / cable feed being talked about is solely for top up / manual override when extra hw is required via the mains rather than via the boiler ?

 

[nv_london]

I'm sorry, you've totally lost me.

Are you asking, if the boiler could still be live? Maybe, but I was assuming that everything was off because I switched the power off. I don't understand how the boiler could still be on. Yet again, excuse my ignorance in this matter.

 

[Space cat]

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.

So, nothing on the pen when you touch it to the wires but something when you're in close proximity. Are there any earth wires in there - maybe connected to a terminal in the back box rather than to the switch itself? What happens if you touch the pen to those?

If they also show dead, wave the pen around the general area, especially near to water pipes. Try touching a few too. You can get a tingle off a dead wire if you're also in contact with metal that should be earthed but isn't.

 

[Click-Sure]

I've worked on houses with a TT supply where there is a potential difference between the supply neutral and the tt earth rod. If the neutral is not disconnected then this could explain things...

 

[nv_london]

Thanks lads. It's just been suggested to me that it could be 'back feed' from the neutral?!?! (Apparently a common situation with the way old wiring was hooked up?! No idea if this is true).....anyway, if I confirm this with a multimeter, i.e. that there is a relatively low reading from the neutral (maybe, less than 20 V?!?), can I go ahead and replace the face plate (still making sure not to touch the exposed neutral wire)?

 

[RF Lighting]

How and with what did you isolate the mains?

Did you turn off all the CU main switches, or just the MCBs or withdrew the fuses?

Volt sticks are great. Mine even lights up if it is near the radiator in my bedroom.

 

[nv_london]

I isloated the mains, by switching off everything at the fuse box and pulling out all the fuses! Everything went off/stopped working, including the neon light at the front of the isolator switch.

While volt sticks may not be the best piece of equiptment, I know this isn't a false positive as I felt the shock!

So after basically rewriting my original post, the question about 'back feed' still stands...

 

[electronicsuk]

I think what you're referring to may be what we prefer to call a 'borrowed neutral". You'll find plenty of info on this with a search, but it's irrelevant if you isolated all circuits, as you still need something to liven up a borrowed neutral to get a shock.

 

[nv_london]

A borrowed neutral would make sense....maybe it's being borrowed with next door?! How 'live' can a borrowed neutral become? I.e. can it reach 230 V? or is it usually less that this, or does it depend on the situation?

 

[JohnD]

Look for those green and yellow wires I mentioned earlier.

They are supposed to protect you from shock under fault conditions, and would normally do pretty good job of preventing what happened to you.

Shocks are particularly dangerous when you are working next to metal pipes and bare wires.

If not properly bonded (green and yellows) then the risk of shock from touching taps, pipes, radiators, metal bath in a bathroom where you are wet and naked are quite worrying.

 

[electronicsuk]

A borrowed neutral would make sense....maybe it's being borrowed with next door?! How 'live' can a borrowed neutral become? I.e. can it reach 230 V? or is it usually less that this, or does it depend on the situation?

It depends on the situation, you would very likely read 230v with a high impedance voltmeter, but as soon as you start to load it down the voltage would drop. Again, exactly how much depends on what loads (impedances) are on the circuit that's borrowing the neutral.

It's technically possible that next door could have borrowed a neutral from you, as that would fit with the information you've given us. If that were the case, the voltage on the neutral should disappear when you turn your main DP isolator on the consumer unit back on, as the neutral current then has a return path. However, I don't recommend doing this, as you then only have SP isolation via the fuses in the CU, and as you have no test equipment you could end up with a nasty shock if you have reverse polarity anywhere in your wiring.

In any case, it's far more likely to be a problem with the earth bonding arrangements as JohnD says. I can't even imagine how a borrowed neutral would happen, unless the properties were originally one and have been split at some point in the past.