Drilled through an electric cable - I think

[jjfresh66]

I know this is a really dum thing that i did and i'm really annoyed at myself and also now concerned. I put a kitchen unit up over the weekend after lots of nagging from my wife - I forgot about the plug socket situated below where the cuboard was to hang. Luckily the electric was already turned off and i only realised that i made the mistake when it was too late.

When drilling i noticed the sound was different so i stopped, then noticed white plastic under the plaster (Gulp) Spotted the plug socket directly in line where i just drilled and nearly had a cardiac arrest. Thank god the electric was off at the time. Anyway just to confirm this, I chipped a little more of the plaster away and i could see the white plastic trunking with a drilled hole bang in the middle of it - the drilled hole is only small so i'm not sure if this has penetrated any cable behind it (could not see any cable through the small hole) Anyway i turned the electric back on, lights etc but no T.V etc - i noticed that one of the trip switches was down and i pushed it back up. Then everything came on and the trip switch stayed up.

I'm now in panic mode as i don't know if this is dangerousor not
Can anyone advise me what to do please.

 

[rjb]

I take you don't have test equipment! Phone a sparky and say what you just posted.

He will test your circuit for insulation resistance and hopefully put your mind as rest. If necessary he can carry out any recification needed.

Don't worry. This happens a lot especially with pictures being hung.

A bit shutting the gate after horse has bolted, but get yourselve a GOOD cable / stud detector for future.

 

[rjb]

I'm removing the post this replaces. I didn't read the bit about RCD tripping.A lesson in not reading very thing twice as I was told as school many years ago!!! SORRY

 

[nozspark]

You say that one of the trips were down.... was it an RCD (wider module with a test button on it)?? If so it sounds like you have nicked the cable and it will need repairing.

You will have to visually inspect this cable as any fault might not show up with testing as your drill bit will have caused the RCD (??) to trip, and now that you have removed it the 'fault' will have gone - but the damage to the cable will still remain!!

The only way to know for certain though is to remove some more plaster over the conduit and then carefully cut into it with a sharp stanley (power off!!!) The way that I do this is to reveal about 2 inches above and below the hole, cut down the side and across the top and bottom of the revealed section (very carefully so as to not cause any more damage - score several times rather than trying to make the cut in one go). Once you have done this you should then be able to peel back the conduit and see what (if any) damage you have caused.

 

[rjb]

and now that you have removed it the 'fault' will have gone - but the damage to the cable will still remain!!

Not necessary. Is you test for insulation resistance by firing 500V down the circuit then if the results are greater than 2M ohms then everything will be fine. If less than 0.5M ohms then there is a big problem.

If the cable is nicked then you may get a reading between the two which indicates you need to do further exploration. If this is the case then bash into the wall.

 

[nozspark]

Sorry, maybe I wasn't making myself clear.

Say you drill into a cable, damaging the sheath and insulation and also causing a N-E fault with your drill bit. Now you remove your drill bit and do an insulation test at 500V, the results are:-

L-N >299Mohms
L-E >299Mohms
N-E >299Mohms

Continuity also checks out!!!

What I am saying is that there is still damage to the cable which needs repairing, do you not think so??

 

[jjfresh66]

Thanks for everyones response so far.
I will have a look closer inspection later, chip more plaster away and cut into it as advised - at least i can see whats happened exactly.
My main concern is that can or is this a fire issue.

Thanks

 

[nozspark]

Is this a fire risk??

If this circuit is protected by a RCD with a maximum rating of 100mA (should be 30mA for socket circuits) then this should trip beofre anything serious happens.

This does not mean though that you shouldn't at least have a look for any possible damage and repair it as necessary!

 

[rjb]

If you've drilled off the insulation so have exposed conductor close together would the results of insulation resistance be as high as you state?

In this case it is easy to access the fault and it will be covered up by thecupboard so yuor suggestion of going into wall is a valid first action to take in this case being pragmatic.

(What has jjfresh66 started )

It does go to show nothing is black and white.

 

[jjfresh66]

Right - I've just been home in my lunch hr because i can't stop thinking of the worst possible scenario i.e. House burning down while asleep.

Took the cuboard off and cut through the white plastic cove ( Very carefully with the electric off), Just my luck it was a double plug socket and there were two cables there. I've drilled through the centre of both, just clipping the lefthand side one. I think i can just see the copper - it's hard to tell (what a plonker)

looks like an expensive sparky's job - our lass will kill me

 

[rjb]

Glad you've found problem and glad your fixing it. If it was plumbing it is obvious something 's wrong - you get wet or see water dripping.

Electricity is a bit more tricky and dangerous.

Is this a fire risk??

I am chewing the cud now. I would argue the OP's situation could be a very real fire risk. If a drill shorts out a cable then the RCD will trip as there was earth leakage when drill head made conduct with a live conductor. However the igitinal arcing can cause the copper the burn away so your 2.5mm cable will now be much less than designed. When you reset RCD the RCD will not re-trip as there is current flowing without leakage and hense there will be continuity, but as copper conductor is less than 2.5 (talking live conductors) this will cause a hot spot as reduced cross section area and potentially therefore potential a fire risk espeically as this is a kitchen situation the load for the socket could be relatively high (kettles etc) . The MCB will only detect over current so that won't necessary detect the fault either.

Another point you said you've drilled through 1 cable completely and knicked the other one. You may have inadvertently broken the ring and now have two radial circuits. The circuit may appeared to be working OK, but for many reason this would be dangerous.

(MY GRAMMAR ARGGGHH!!)

 

[NickStone]

I know this is a really dum thing that i did .

You're not alone. Did the same thing when hanging a mirror.

 

[rjb]

And so did my double glazing fitters!!

(When fitting French Windows, not hanging a mirror for me. Mrs RJB can hang a mirror )

 

[viewer]

One answer, which may not be acceptable to you, would be to put the socket on the ring in the cupboard (through neat hole and properly fixed to wall at rear). The socket below could then be on a spur if still required and so the chiselling of the wall would be behind the cupboard and damage to tiling etc limited.
V

 

[bernardgreen]

You are not alone.

I installed a new run of triple and earth to a new switch. Then putting the door framing back I put the tip of a screw ( longer than it should have been ) into the new cable.

Note the length of internal damage due to a small pin hole. The outside of the cable showed no damage other than the pin hole