John,
Thanks for the advice...
I can see that if the leak is a complex device (switch-mode power supply for example) rather than just a resistance then the multimeter won't read it properly, or at all. But if it is a resistance such as a leaky cable due to decaying insulation I'd have thought 82 ohms should show up nicely? I realise I'm pre-judging what the problem is, though...
OK, I was going to do a "BInary chop" with what I think is the sequence - starting with dividing it in two, then successively divide the faulty half each time until only one part is left. I think this results in the fewest disconnections needed?
Is there a good way to replace a cable in-situ? Again, lifting floorboards will be a major undertaking. I know the existing cable isn't clipped (none of them are), so I suppose the obvious way is to pull it out with the new one attached and hope it doesn't get stuck on the way, and/or get disconnected. But would it be feasible to use rods with a ring on the end around the old cable, pushing it along like a curtain on a rail? At least if this goes wrong there's nothing to stop me trying again, or trying another method. Pulling through the old cable seems such a risky one-shot deal!
I wonder if I'll find that one of the cables feels warm when I go to disconnnect it from a socket?
Cheers,
Howard
Thanks for the advice...
OK, I was just going to turn off the MCB - is there a reason this isn't enough? When the CU was changed (2004, of course!) I put in a couple of sockets on the downstairs ring near it, one on each leg of the ring, so I can work from there rather than having to open up and delve into the CU, so I was thinking that just turning that circuit off would be enough. It's going to be tricky reaching and working on the sockets as it is, without doing it in the dark!Turn off all the power at the main switch as well as the MCB, and remove all other loads from the circuit. If you measure the resistance with a simple multimeter, you will find that the resistance between L and N is so high you can't measure it, if there is no load on the circuit.
I can see that if the leak is a complex device (switch-mode power supply for example) rather than just a resistance then the multimeter won't read it properly, or at all. But if it is a resistance such as a leaky cable due to decaying insulation I'd have thought 82 ohms should show up nicely? I realise I'm pre-judging what the problem is, though...
Unfortunately the route of the ring doesn't seem to be obvious - a couple of sockets are on spurs, chased into the wall behind cabinets, and without lifting floorboards (and the stuff on top of them!) it will be tricky to work out where it all runs. If I assume most sparks will just run the shortest route around the outside walls I can guess the order, but can I rely on that?if the unexplained usage is on a ring, try to identify and draw the route that the ring takes. Remove a socket on each of the clockwise and the anticlockwise legs of the ring, so you interrupt the ring and any sockets between the interruptions will have no power going to them. Put the cores safely into chockblock.
If the load now disappears, you know it is somewhere between the two interuptions.
Interrupt the remaining part of the ring to narrow down the place where the hidden load is. And again. Eventially you will find it, or at least identify a length of hidden cable within which the fault exists. You might end up isolating that section and replacing with new cable.
OK, I was going to do a "BInary chop" with what I think is the sequence - starting with dividing it in two, then successively divide the faulty half each time until only one part is left. I think this results in the fewest disconnections needed?
Is there a good way to replace a cable in-situ? Again, lifting floorboards will be a major undertaking. I know the existing cable isn't clipped (none of them are), so I suppose the obvious way is to pull it out with the new one attached and hope it doesn't get stuck on the way, and/or get disconnected. But would it be feasible to use rods with a ring on the end around the old cable, pushing it along like a curtain on a rail? At least if this goes wrong there's nothing to stop me trying again, or trying another method. Pulling through the old cable seems such a risky one-shot deal!
Yes this had occurred to me - despite my signature, there is no smoke, smell or any warm spot apparent. I suppose that it could be a length of cable that's leaking all along, so the warmth will be well spread and not noticeable - but it will be interesting to find what was happening regardless of the fault-fixing!700W is as much as a small electric heater, so I will be surprised if you can't find it once you know where to look, because it will be hot, or possibly scorched and melted.
I wonder if I'll find that one of the cables feels warm when I go to disconnnect it from a socket?
Cheers,
Howard