OK I now I am a complete idiot but I just drilled through a mains cable. Big
flash then the RCD trip switch kicked in and put all the power in the house
out. However, when I put the power back on everything works no circuit
trips? So I put an insulated screwdriver in the drill hole to check and
everything trips again, the end of the screwdriver also got pretty melted.
Reset trip switches and everything works fine.
I am having someone with a brain, unlike me, look at it tomorrow - an
electrician. But is it safe to leave the power on overnight - the lead is
below a floorboard but can not be accessed without a fair bit of work -
skirting off etc hence the wait for the man with a brain. I am concerned
that something may be smouldering away under my floorboards or if that was
the case would the RCD/MCB kick in?
PS Try to limit the comments on my stupidity and about how cheap pipe/cable
detectors are. my wife wants to kill me as it is - take pity on me!
PS We have all done it. The rules are to damage the CH cable on the coldest
night of the year, the lighting circuits just before nightfall and the ring
main just before a film you have wanted to watch for ages is due to start
Oh dear. You can get an RCD trip by connecting earth and neutral
together but since you had a flash then it is live and either neutral
or earth or both.
I don't think that it's a good idea to leave the cable powered,
especially since it is hidden away. This would be a fire risk.
Do you have any way to identify which circuit the cable is other than
poking a screwdriver into it? If you have a mains testing
screwdriver you could put the tip *near* the cable and you *may* get
an indication that it is live. Then you could selectively turn
breakers off until you find which it is.
If you can't do that, then you should turn the power off for safety I
Regarding the other issue - flowers or a nice dinner, but not today.
To email, substitute .nospam with .gl
Andy and others thanks for the replies.
I have tried to isolate by using a mains testing screwdriver but there are 4
or 5 mains cables running near each other so the screwdriver does not give a
I have noticed something odd in my consumer unit though, my MCBs are the
type that go to the mid way mark when they trip, you then have to push them
all the way down and all the way back up to reset. The one for my cooker is
just all loose and floppy although the cooker is still working, could this
be a knackered MCB but one that is still letting power through?
Think the best one along these lines is that when a chap drilled
through the cable all the power got cut,he couldn't connect the
fact that with no power the mains drill would no longer work,
he then took the drill to bits to "fix" it couldn't put it back together
so had to buy a new drill., (was on Britain's worst DIYer).
Yours S. addy not usable (not that you would try it) ( )
Utinam logica falsa tuam philosophiam totam suffodiant! / \
Oh boy done that twice in my life!
Once on that side of the Atlantic, in that instance it was fairly obvious
what we (I) had disrupted; the lights in all the bedrooms! So we removed the
fuse for that circuit and kept an eye on it until we went to bed.
We did toy with the idea of turning off 'everything' overnight but decided
The second time was on this side of the Atantic where we (I) cleverly
drilled through a wooden floor joist at angle while completing this wood
framed house; and ..... fssst! Splat! Into 115/230 volt house wiring.
Fortunately everything was exposed and it only took about ten minutes to run
a new piece of cable; minus the time spent cursing myself!
Take heart from the fact that I did the same thing about 20 years ago
in a previous house. And we didn't have RCD's in them days.
It was a very useful lesson - subsequently I've always (without fail)
checked for cables buried in the wall and take special care if there
are sockets on the wall, or on the far side of the wall.
And I am always conscious if the drill appears to suddenly change in
terms of physical feedback which could suggest it has stopped drilling
brick and is now drilling something which isn't brick.
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I didn't do this, but had to fix an identivl situatin in a rented place
- I was pianting it an FLASH as you desribe. Emuslion pain in old screw
hole with plug...
The electrician who came (via a call to teh letting agency) simply
chased the wire out, and crimped on a new bit. We wrapped it all in
insulation tape and I plastered it back where it came from.
Yes, it was in the end that simple.
from my experience of such circumstances, Damage to drill
bit/screw/driver is far vorse than cable damage.
With RCD cable damage is often nothing more than slight loss of sleve.
chase out onough wall to get a few turns of good insulation tape around
mising sheath then plaster back in. I'd be inclined to patch up existing
cable than cut out and crimp a new piece in.
The Worlds No1 Fitness & Gym Equipment/nutrition specialists.
Oh, FFS! The original poster has had fault currents coursing through this
little stretch of the cable not once, but twice. The first time he's had
"a big flash"; the second time the fault current was enough to do damge to
the end of his tool (a screwdriver, before you ask). That amount of
energy released before his protective devices kicked in strongly suggests
a hefty live-to-neutral flow, rather than a benign neutral-earth short or
even a quickly-cleared live-to-earth. Assuming a modern installation, the
main lengths of the cables ought to be OK, as the protective devices are
specced to act quickly enough to limit the temperature rise in the
conductors to below PVC-melting/softening point. *BUT* at the point of
the short, the insulation and immediate conductors *will* be damaged,
and it's irresponsible not to cut out the cable in the immediate area of
the drilling and extend with a nice new bit.
With a bit of luck it might be possible to run a new length of cable to
the nearest fitting in one direction without too much disruption, and
make the join to the old cable in the other direction either by crimping
or in a new wallbox fitted with a blanking plate, to act as a permanent
reminder when next drilling, or maybe a wall-clock connection point ;-)
Failing that, replacing the run of cable between the two existing fittings
it serves makes for a decent job.
Patching up the injured cable with "a few turns of good insulating tape"
is an approach worthy only of the spur-wearing mob...
|Stefek Zaba wrote
| ... in a new wallbox fitted with a blanking plate, to act as a
| permanent reminder when next drilling, or maybe a wall-clock
| connection point ;-)
"We'd always wondered why the previous owners had a Smiths Selectric Sun-Ray
wired into the cooker circuit"
This is a very dangerous idea.
The insulation is likely to be melted locally around the damage and
the conductors will not be at their original condition even if the
damage had only been slight. At best the continuity in the cable
is going to be unreliable, and at worst it is a fire risk.
Considering that the cable is also hidden and going to be hidden
behind decorations that will be inconvenient to replace.
Cutting in a piece of cable with crimps is a 5 minute job. Making
good the decorations will take longer.
It's silly bodging a job when it can be done properly and safely.
To email, substitute .nospam with .gl
Well It is all sorted now. Basically, there was enough slack in the cable to
cut out the damaged portion and fit a 30/40 Amp junction box to join the two
sides of the cable. It was the old feed for the cooker which now just feeds
3 sockets as we have a gas cooker.
I was suprised by this whole thing because I was drilling and screwing along
the joists as I have done to floorboards in the past. However, when the
board was lifted you could see that someone has previously cut a fair size
hole in the joist from its top i.e. u shaped and fed a few mains cables
Is/was this normal practice? I always thought following the joists was quite
safe, I am begining to wonder if any of the other boards I have screwed down
over the years, about half the house, may have screws perilously close to
wiring. Although where possible I have always tried to look and work out the
routing of wiring piping etc. I just got carried away yesterday as it was
one of the last boards along the line of the joist.
What is/was normal practice?
Regards and thanks for the replies.
Do you mean a junction box with screw terminals? If so, they are not
supposed to be used in concealed places according to the Wiring
Regulations - there needs to be access for repair. I believe that
the theory is that screw terminals are considered to be liable to
coming loose over time. Hence the discussion about using crimps.
These are permitted for concealed joints.
Again the Wiring Regulations come into play. Cables are not
supposed to be installed in notches in joists. The requirement is
that they should be at least 50mm from either surface, so the
convention is to drill through the centre of the joist and thread the
cables. If there is a need to go nearer the surface, then the
cables must be covered with a substantial shield - typically a thick
steel plate which must then be earthed.
In any case, it is not a good idea to notch joists if at all possible
because it does weaken them.
Not sure about the screw terminals as an electrician did it not me.
The wiring for the house was done in the early 70's would cut joists have
been OK then?
The wiring was tested when the new consumer unit with RCD and MCB's was
fitted 3 years ago and found to be sound - until I trashed it yesterday!
the wiring wasn't tested !
the circuits might have been tested for loop impedance
and insulation values but the wiring was certainly not
'tested' - i.e. search for buried junction boxes and
sound - only in the vaguest terms probably
- until I trashed it yesterday!
Are you suggesting that buried junction boxes and notched loits are
routinely checked before fitting new consumer units?
I poked at it twice because in my panic to restore power the first time I
did not make a note of which MCB had tripped. I used thick rubber gloves and
an insulated elecrticians screw driver. I also knew the RCD would cut in
again - not a great idea I admit but I was happy with the precautions.
"Chris Oates" <none> wrote in message
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