Just nailed through lighting cable

14 Jun 2006
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United Kingdom
Hi guys,

I have a question: I was just securing a loose floorboard down with a nail and all the lights went off. Pulled the nail out, checked the fusebox and it looks like the fuse has blown (although I can't be 100% sure) so my question is this: Can I simply buy a new fuse in the morning, install it and everything will be OK ... or not?

If I get the fuse and the lights still don't work, what's the next step? Electrician?

I swear I'm never doing any DIY ever again!


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If you've damaged the cable then you need to fix it. Sounds like the cable is installed in a notched (as opposed to a drilled) joist. This is indicative of a cheap and nasty rewire some time in the past. (Let me guess; property built in 30's or 50's and rewired around 1980?)

Might be worth getting in a qualified spark to inspect.
Thanks for reply ... yes the house is a terrace built in the 30s, not sure when it was rewired I've not long moved in.

What'll happen when I change the fuse in the morning? Is there a chance of a fire?
There's a fair chance that nothing untoward will happen, at least in the short term. Your nail might have shorted between live and earth and then left a gap when removed. But the fact is the cable may well have been damaged (unless it's a coincidence) and you should investigate and rectify the problem.

There's no point in brushing it under the carpet and hoping that it doesn't create a problem for the future.
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It's funny you should mention carpet - I'm having a new carpet fitted tomorrow, hence my need to fix the creaky floorboard!

So if I remove the floorboard in the morning, what am I looking for to indicate the cable is knackered? Exposed copper?
OK I'll take a look. First stop B&Q, replace the fuse then lift the floorboard to check the damage ... all before the carpet fitters come.

Thank you for your help dingbat,

I'd suggest you lift the board before replacing the fuse, when you are in B&Q pick up a 20A junction box (get a good make like MK), I know you shouldn't put junction boxes where they are inaccessable, but get the screws tightened properly and it won't be a problem (and will be much, much better than a nailed through cable)
And I'll back Adam up here. Fix the problem before you change the fuse - what's the point of replacing the safety device without repairing the fault that caused it to operate?

Remember fuses don't 'fail', they do their job and disconnect a faulty circuit.
Sounds like a good idea, I'll pick one up.

What if I don't fit a junction box - what kind of problems might I encounter?
If you dont fix the cable NOW
1 You could have an open ring
2 It could arc & cause a fire

There might be a 3 & 4

But if you do have latter problems as well as lifting the floor board, you will have to lift the carpet.

How can you even be thinking of leaving it.
The only reason I was considering leaving it is if I do lift the floorboard up, what if I cause further damage to the cable? Just hammering a nail through it damaged it once, I don't want to make it any worse.

Just been to B&Q and got the bits, put the fuse in and everything's back on.
When you have the board up, you take note of where the cables are and when you re-fix it you excercise care to avoid doing it again

You better lift it and check it out, you could have left the circuit with no earth, live conductors exposed, conductors reduced in cross section, current tracking across it, etc

Get it lifted and check, your new carpet won't look good with a burnt patch in the middle :eek:
Just taken the floorboard up, theres a small hole in the cable where the nail went in. It didn't go right through, and there's no sign of scorching.

Should I still cut the cable and fit this junction box?
Yes, and remove the smallish section where the nail went in (it'll be a bit burnt from the short circuit current that flowed)

Make sure you get the screws on the JB nice and tight, but not so tight that it shears the cable, along with other good wiring practice such as keeping the unsheathed cores entirely within the JB, using earth sleeving, fitting the lid in the right orientation that it blocks off unused cable entries, etc

(Sorry, I'm not quite sure how experciencd you are with electrics, so ignore me if I've been stating the obvious)

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