Electrics that go with a bang!

[Anonymous]

Hi All,

I think I know the answer to this (it involves £'s and an electrician) but I thought I'd share....
So the refurb of our dining room is taking shape, I note the distinct colour change of the brings / mortar from the damp proofed flooring up to about a metre high as that bequeathed to me by the moron's who owned the house before me but I digress....

I finally bit the bullet and decided to move the electric sockets from their dangling from the ceiling to a more safe fixed to the wall position. This required me to shorten the existing cables, terminate with junction boxes then run cables from the junction box to the wall box positions, no problem so far....

So I turn off the power to the ring main... I plug in a lamp into the existing socket and voila no light... I check the light in a different socket on a different ring (it works). I take the front off the socket and test with my meter no voltage / amps etc... all good so far.

I start to cut through the cable (to shorten it for the junction box) and BANG piece of pliers now vapourised and a black mark on the cable ! Shish Kebabs I'm thinking at this point. Confusingly nothing has switched off in the main fuse box... shared neutral or something ???? Confused...anyone any thoughts apart from call a sparky!! ?

The electrics are pretty modern and were certified in 2003... House is C18th but I'm hoping the wiring isn't !!

 

[a twig]

Cut the wrong cable? :twisted:

 

[a twig]

In a more serious vein - one for two things spring to mind:

1) Dodgy ground/earth - main breaker off and get metering to find out if this is the case.

2) There was an appliance on the ring main which had a large capacitor in it - which you discharged by cutting the wiring - i.e. nothing to worry about

 

[Flyfisher]

Very odd, given that you had explicitly tested the socket before cutting the wire. Is it possible that someone else had switched the circuit back on without your knowledge? I've known that to happen when lots of people are on site and it's why many (all?) commercial installations have the ability to physically lock open a circuit so that no one else can re-energise it.

I once had to do some work on a socket and was using a plug-in lamp to confirm the circuit was dead, but couldn't find the fuse - and it was only a small CU! I methodically went through removing each fuse, even the lighting ones, but couldn't isolate the circuit. It made no sense. So I decided to remove ALL fuses (which did isolate the socket in question) and then replaced the fuses one by one. I discovered that the socket was fed by TWO fuses! Subsequent laborious investigation revealed that the socket had been wired across two separate ring mains!

However, while that's an example of why assumptions about wiring should never be relied upon, it wouldn't explain what happened in this case.

Hmm.

How exactly did you "turn off the power to the ring main"? Does the CU have MCBs and/or RCDs?

 

[steveb]

when you checked with your meter, did you only check for live/neutral voltage or did you do live/earth and neutral/earth too - I tend to be paranoid and check all three!

 

[plasticpigeon]

Yes I can't add any more than other people here, but a useful tool is a plug in tester that tells you if the plug has been wired correctly. They are only a few pounds. i like to plug one in after I have been doing wiring just ion case I've got things crossed. No better than a meter, but a bit more handy.

 

[a twig]

Yes I can't add any more than other people here, but a useful tool is a plug in tester that tells you if the plug has been wired correctly. They are only a few pounds. i like to plug one in after I have been doing wiring just ion case I've got things crossed. No better than a meter, but a bit more handy.

Just a note of caution, a lot of plug testers can't tell the difference between a properly wired ground and a ground that has been wired to a neutral though - something that a lot of historical cowboys and under-informed DIYers used to do.

A decent non-contact voltage tester is usually the minimum to ensure a cable is really dead. Use that as a first step, then if it indicates that something is live, use a decent meter to find out what.

If you are going to do a lot of DIY work something like this - can usually be found for around £25 - its as idiot proof as these things get, there are no knobs and dials to forget to set correctly, or leads to plug/unplug wrongly, and it is easy to use with two hands as well:

 

[Anonymous]

Hi All,

thanks for all the responses... I have a meter and I checked both live neutral, live earth and neutral earth (not 100% on the last one but I think I did)... I also plugged a working lamp into the socket and confirmed that the lamp didn't light.

The only other person in the house was my wife who was hoovering in the same room as me at the time of the BANG !

I think the only thing to do is to get a sparky to come and take a look. I will be turning the power off to the whole house from now on !!!

thanks again.

Paul.

 

[noj]

hoovering in the same room as me at the time of the BANG !

Same ring main?

 

[Anonymous]

Hehe sadly no... via extension lead plugged in, in the kitchen (which is on a separate ring) (well I thought it was !!! )

hoovering in the same room as me at the time of the BANG !

Same ring main?

 

[CliffordPope]

So I turn off the power to the ring main

How? Could you break both live and neutral, or rely merely on pulling the fuse out?