Help Required. electrical circuit problem

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(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 without problem. 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)
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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.
Rob Graham
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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.
Dane
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Dane Koekoek

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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.
Bob
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Thanks for the brilliant advice, it has helped me alot but I'm a little stuck...

FCU/power came online

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 out.
Any more ideas you can give me would be greatly appreciated.
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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.
Bob

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week. Do you think I'll be okay leaving the two radials on until then?

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 knows where. 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.

could figure out what the problem is.
You've been a great help.
Kev.
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Yeah should be fine Kev

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 retry.

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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?
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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.....
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Martin

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Martin is right. Can you bypass the problem with a new piece of cable either temporarily or permanently? If you can your problem is solved. Afraid your test didn't prove a lot really.

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Thanks to both of you for your help; I wish I understood as much as you guys.
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No problem at all Kev. I'm an electrician by trade though my work is more management and IT these days. I'm sure you could blow the socks off me with your profession.
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Hey, how do you think we got started ... same way you are. There's no substitute for experience.
Best wishes
Martin
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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 long wait!!)
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
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Oh but if only life was like that :-)

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.
It does

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.
Good Luck
Bob
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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)
Then ...
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.
HTH
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Martin

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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.
Martin
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oh dear!! poor guy is going to kill himself(or burn his house down)

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<snip>
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 control :-)
... but purely out of curiosity, could OceanTragic please let us know if he's still breathing...?
--
Martin

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