where does my spur connect?

[dnel]

Hi, when I removed the old airing cupboard from my house, I discovered an live power cable under the floor of the cupboard. I've spent some time now trying to figure out what it's wired into but it only appears to go dead after I kill all the power to the house, either by the master switch or all the circuit breakers.

I have 5 in the MCB, 5/5/20/32/32 amps, 2x lighting, boiler, oven and ring main as I'd expect, it seems to be feeding power from both the lighting and ring main, disabling the ring main reduces the power of the signal I get from my power tester, while the boiler and oven circuits seem to have no effect, turning off the lighting by themselves does not kill the power to the cable.

I'm getting quite concerned because the cable was left in a very dangerous state when I found it, live and with bare wire exposed, clearly no attempt was made to make it safe. I'd like to find where it's connected and remove it. Is there any ideas how this might be wired in? I'm assuming it used to be used for an immersion heater.

Following the cable under the floor, it takes a left turn, which passes two sockets, I've disconnected both with no effect. one of the sockets has a spur but I'm not sure where to. If it carries on it may go right back to the MCB but short of pulling up carpet and floorboards I've no way of knowing.

 

[ricicle]

What instrument are you using to test this cable ?

 

[dnel]

its a stud and electric cable detector

 

[rjm2k]

Is the cable connected to anything at the end away from the board or is it just bare unconnected wires? Does your board have a breaker marked immersian heater or anything?

 

[dnel]

they were bare unconnected wires shaped in a fork, I've since masked them up for safety.

I can't see any evidence there's a dedicated circuit on the MCB, the empty slots are all masked up.

 

[securespark]

You need a two pole tester to be sure of correct confirmation.

You can buy one for a tenner and use it on other electrical jobs. They're OK for battery testing too.

 

[Maxatoria]

It'll be quicker and safer just to start chasing the wire by pulling up carpets/boards as you'll be able to follow it, just turn off the power and try not to pull too hard on the cables as you don't want to disturb stuff thats not been screwed down properly and cause even more trouble and it probably wont take more than 15-20 mins to find the origin but i'd put a few quid on it being under a wardrobe

 

[dnel]

You need a two pole tester to be sure of correct confirmation.

You can buy one for a tenner and use it on other electrical jobs. They're OK for battery testing too.

I have an multimetre, I could give that a go, just a bit wary having never used it on anything close to mains voltages

 

[dnel]

It'll be quicker and safer just to start chasing the wire by pulling up carpets/boards as you'll be able to follow it, just turn off the power and try not to pull too hard on the cables as you don't want to disturb stuff thats not been screwed down properly and cause even more trouble and it probably wont take more than 15-20 mins to find the origin but i'd put a few quid on it being under a wardrobe

I'm sure it is, but my problem is once I start dismantling things, I get dragged into another big DIY job! I'm actively trying to avoid starting on the back bedroom the cable runs under until I finish the front bedroom renovation. I suppose this is the DIYer's curse!

 

[Maxatoria]

perhaps take the cover off the fuseboard and take a photo of the board as it maybe that they've just popped it in with something else like the cooker and it may be a quick 2 sec job to pull it out of the board

 

[rjm2k]

only appears to go dead after I kill all the power to the house, either by the master switch or all the circuit breakers.

If switching ALL of the breakers of isolates this cable then that suggests that it's actually just 1 of them isolating it or it's not really live, or it's somehow connected to all the circuits through a fault?

 

[ericmark]

There are a number of possibilities.
* It may not really be live but due to running alongside a live cable inductive and capacitive links have given it enough voltage for the detector your using to flag it as live.
* It is not unknown for a ring to be feed from two fuses/MCB's clearly it should not be done that way but mistakes do happen.

As an electrician I have many meters all able to measure different things. There are a number of ways to work out where it is being powered from. Putting a known load on the cable say a fan heater and then using a clamp on ammeter one can quickly work out which cable is supplying it.

Often it is a case of calculated guess work. And some times even we are stumped.

My daughters house has all radials yet at the old fuse box it seemed there was a ring. We have guessed that some time in the past the consumer unit has been moved. This is supported by the fact the orignal garage is now a room. What we will guess is that a junction box has been installed where the old consumer unit was. And that was in turn feed from the new one.

So to be on safe side 25A not 32A MCB's have been used when moving from fuse to MCB with RCD protection.

Really we should knock holes in the wall and find the junction box but we really don't want to do that.

Your in a similar position. All well and good saying physically trace the cable but in real terms one has to be realistic. But electricians do have tools and toys you only dream of and to hire them is so costly that likely best option is to engage some one who has the tools for the job.

The CAT generators and detectors will find a cable 4 foot under the road clearly far more sensitive than your DIY tool. The bigger the firm the more likely they have the CAT tools. You could of course ask before engaging them.