(I hope this is an okay newsgroup for this article, if not, which other
ones are more suitable.)
Today all the electrics went off in the house.
My wife managed to insolate a problem electric circuit and hoped it had
a blown fuse, but it wasn't that.
The problem circuit provides electric power to half the house.
All other circuits (7 of them) are fine.
When I put the fuse holder back in the fusebox and switch on the
electrics the circuit breaker which protects the power to the house trips.
When the fuse holder is out of the fusebox the power can be switched on
I have tried using one of the other matching 30a fuses on the problem
circuit and the same problem occurs.
I have switched off all fused-connection units on the circuit.
I have unplugged all devices from all sockets.
Still no joy.
I don't understand why the problem started as no changes to the
electrical system have been made for a couple of years. The electrics
are less than 15 years old.
Could the problem be that something in the ring has gone wrong? If so,
what's the best way to test for this? Do I just need to check each
socket and continuity test the circuit wires?
(Thanks in advance for any help)
At least you've isolated the circuit. You'll probably need to look inside
each of the sockets on this circuit to see if a wire has come loose. I don't
know why they should, but they just do, sometimes. The loose wire then may
end up touching somewhere it shouldn't.
Is there an immersion heater on this circuit? If there is, it might have
blown, shorting itself out, tripping out the circuit. My parents had exactly
this problem a few years back.
Basically take everything off the circuit and then reintroduce the
appliances until one trips the power - then you've found the faulty
appliance or wiring.
Right, this is what you need to do.
First. Don't panic, everything will be all right,
Second, In your fuse board take one a live and neutral from one leg of the
ring so effectively you have a long radial circuit.
Third, split the ring at a socket , protect with terminal strip each end and
energise with the fuse. If the fuse holds you know the fault lies beyond
your split. If the fuse trips then the fault is before your split.
Fourth, repeat at various points until you identify the precise area where
your fault is and then check this area out in detail.
To quicken the process ask yourself if any floorboards have recently been
nailed down or any pictures or cupboards hung.
Good luck with it.
Thanks for the brilliant advice, it has helped me alot but I'm a little
Great idea, I didn't realise I would be able to do this
I split the circuit at one socket and lots of sockets and the boiler
FCU/power came online
As so many sockets had come online, I disconnected the first radial,
connected the other radial and started testing it as it seemed to only
serve 1 upstairs socket, 2 doubles and 1 FCU downstairs.
I split the second radial into two and the upstairs socket, 1 double and
1 FCU came online, leaving only 1 double socket, which is quite close to
the socket I used to split the original ring.
I took this circuit apart and there was a little water in the socket
(its near the sink - it wasn't me that put this in, or splashed the
socket!). Aha, this'll be the problem then I thought, but no, as I
replaced the socket with a new one and still got the same problem..
The problem must be in between the very first socket and the one that
had the water in it.
The current situation is that I have power to everything, except rather
than a single ring I have two radials. Is it okay to have two radials on
from the same fuse in the box?
There's obviously something wrong with the wire that would join the two
radials together but I can't figure out what, or how to sort the problem
Any more ideas you can give me would be greatly appreciated.
By converting to a radial it allows you to test the circuit a bit of the
circuit at a time. What you are doing is narrowing down the possibilities
until you find the area where the fault is. When you fix the fault you need
to restore the ring.
If I understand you right you've now narrowed it down to a specific area.
You now need to look at this area in detail. the water is suspicious. Is
there a socket in the bedroom or whatever room is directly behind this
socket? If so it may be only a few inches from your wet one and might also
be wet. Is there a junction box nearby (under the floorboards) that the
water may have run into by following the cable.
If all else fails you will have to get the boards up and check the problem
area in detail. Have you checked for nails, screws etc?
Good luck, I think you're getting there.
Due to other commitments I'm unlikely now to sort the problem out for a
week. Do you think I'll be okay leaving the two radials on until then?
Looking at the lie of the sockets I think that they are directly
connected, so I did a continuity test on the wires and got a perfect
result. But there could be a socket or something somewhere, but Lord
Both sockets are in the kitchen and the wires seem to run upstairs on
one, but the other runs sideways and is puzzling.
Behind the solid (two brick width) wall is my neighbour's garden. I'm
starting to wonder if he's been drilling anything, but he'd have to
drill through two bricks to affect any of my electrics, so I'm clutching
at straws I think.
I think the floors will be coming up next weekend. Damn shame, wish I
could figure out what the problem is.
You've been a great help.
Did you test between L-N or L-E? A dead short would indicate the fault.
Conductor continuity being ok doesn't rule out a fault on that cable.
But there could be a socket or something somewhere, but Lord
Not feeding a spur is it? Dish washer, Washing m/c, Central heating. If so
switch of the cord outlets (or remove the fuse if it is this type) and
I didn't do either test.
The ends of each radial are wired into sockets (which work). Between the
two sockets is the cable where the fault lies, which I don't think has
any other sockets/units on it. The cable goes in to terminal blocks for
each individual wire.
I tested Live on one end of the wire to Live on the other end, and the
same for Neutral and Earth. I got continuity each time.
Did this test prove anything or was it a useless test?
I guess it would have been useful to test Live at one end to Neutral
(and then Earth) on the other end as I guess this would have proved any
short between those wires. WDYT?
If you've identified (by elimination) the bit of ring cable that seems to be
giving the problem, I suggest you by-pass that existing bit with a
loose-laid bit of 2.5 T+E and re-test before doing anything more drastic.
IME, the cable going faulty is less likely than something going pear-shaped
with one of the adjacent sockets.
Also be aware that slight leakage in a number of places can "accumulate" to
the point where it trips the thingy. So slight (and hardly visible) damp,
for instance, in each of the kitchen / utility sockets - or the devices
plugged into them - could be causing the problem.
Just my two volts-worth.....
Here's an update:
Just as a reminder I have two radials with the cable that used to join
them together being identified as where the problem lies.
I've re-connected the duff cable to one of the radials and it still
trips the breaker. (Shame it didn't fix itself automatically after a
I put a new cable in to join the radials and everything worked fine. I
could just go ahead and put this in place but it'll take me quite a
while and I'd really like to find out what the original problem is. So I
ran a few tests...
Tested continuity on duff cable:
1. at one end of the cable I tested L-E and N-E and no problem exists,
but this was only with a simple continuity test. Martin mentioned that I
need to test using "an insulation tester that puts 500V across the
conductors" but I'm not sure my simple multimeter can do that. It does
other options for resistance (2Kohms, 20Kohms, 200Kohms, 2000Kohms) but
I've never used these. Are they any use?
2. at one end I linked L and E and at the other end tested continuity
and results were as expected
3. at one end I linked N and E and at the other end tested continuity
and results were as expected
4. at one end I linked L and N and at the other end tested continuity
and results were as expected
What the insulation test does is to introduce double the supply voltage to a
circuit. Sometimes a circuit will test OK at the voltage of a continuity
tester but as soon as mains voltage is introduced, the insulation breaks
down. Apart from that the IR tester is basically an Ohmmeter and you would
expect to see at least 1 Megohm between conductors.An insulation resistance
tester comes as a suite of testers that electricians have. Your tester won't
do it I'm afraid.
If your meter is not autoranging you would have to select these levels
depending on the resistance you were measuring. Let's say you were in 2K
ohms you were measuring open circuit, you then switch to 20K ohms and try
again until you find a level that gives you a reading. If you get to 2000K
ohms and still showing open circuit then it is an open circuit (at least at
this voltage it is)
Good to hear your making progress. If you really want to find out what the
problem is your going to have to follow the wiring between the two good
points and see what's up.
Without the tester mentioned by a different Martin, if you're really curious
you could try safely insulating one end of the duff cable, and then ....
1 Connect just L on duff cable to L on the good ring
2 Connect just N on duff cable to N on the good ring
If either of these causes a trip, it suggests that something has penetrated
the cable and is causing leakage (presumably to a "natural" earth)
3 Connect just L + E on duff cable to L + E on the good ring
4 Connect just N + E on duff cable to N + E on the good ring
5 Connect just L + N on duff cable to L + N on the good ring
One (or maybe 2) of these will probably cause a trip - so you may be able to
narrow it down to which core is playing up.
I assume you haven't got access to much of the duff cable at either end -
but if you have, then chop off a few inches from each end and retest.
Unless the cable has been penetrated, you may well find the defect is very
close to one end or the other.
Original Martin here:
I agree with Bob and the new Martin.
At the stage you've reached, an insulation tester (500V) would merely
confirm what you already know - your RCD is effectly your insulation tester.
A tester could tell you whether the leakage is from L or N, but you still
need to replace the cable so that'd be of passing interest only.
Martin's final point is worth noting: if the fault is not the result of a
penetration of the cable (nail, dead rat's mouth bridging the conductors,
cable resting on a hot source (> 70C).....) then the chances are that snag's
in the last inch or so, and as you've decided to replace the cable anyway,
if you have the slack, (big 'if') it's worthwile lopping off the end and
seeing if that does it before ripping up the floors.
The replacement cable will be the same type (current rating) - 2.5mm sq
twin and earth, I assume - and not some length of flexible cable you've
found in the garage - that's a statement not a question!
Let us know what you found - there must be dozens of people as anxious as
you are to know the cause of this snag.
The guy's merely going to kill himself - I cannot see how that can possibly
justify the use on a Newsgroup of the highly offensive expletive "oh
dear!"... you really must keep your emotions and language under better
... but purely out of curiosity, could OceanTragic please let us know if
he's still breathing...?
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