RCD tripping - nothing plugged in

[JohnD]

Idea: If it's a load that comes on at random times (

Very common with a fridge or heating

 

[martinxxxxxx]

Hi LadyJane

This is really nosey but would you mind sharing how much he is charging you for this fault-finding, if you can bare to state it .

I often get involved in this sort of thing and I have yet to fail to narrow it down to a particular run of wire in within an hour or TWO. So I always get concerned when I hear of cases where it is taking an extended time to locate the fault.

Good luck whether you share the info I have asked for or not

Martin

 

[LadyJane]

The electrician has said it was the live circuit earth test that must have blown the fuse in his machine.

sounds like he forgot to set it correctly. An easy mistake, everbody does it at least once.

I phoned electrician and apparently it's a test he always does on a live circuit to measure earth looping, he called it the 'zed S' test. The fault on my socket circuit might have caused it to blow the fuse in his tester. He is now asking how I am becoming so knowledgeable in the electrical world and where do all the suggestions come from. So I have confessed to coming on here. He has not heard of it before, but is curious to see what I have written about him. lol

Hi John D- There is no fridge on this circuit, it's just living room, dining room, and hallway. That was first item we unplugged, when trying to identify the tripping.
Hi martin - thankfully so far no charge. He has worked for family before and spent about 1/2hr on phone the first night, he came for half an hour yesterday, then his machine broke. He is a local electrician with a good reputation and we know he won't overcharge. He is doing a rewire at the minute on another property and has kindly given up some time to help us in this little emergency. He will give us a price to fix the problem once found. He is coming back tomorrow as he hasn't got a spare fuse for his machine.
thanks to all responses, looks like there are a few of us interested in the answer.

 

[JohnD]

I phoned electrician and apparently it's a test he always does on a live circuit to measure earth looping, he called it the 'zed S' test. The fault on my socket circuit might have caused it to blow the fuse in his tester.

 

[WabbitPoo]

Might it coincide with say, the heating or hot water coming on? Just a stab in the dark, but you do seem to be searching for a fault that seems random!

 

[LadyJane]

Hi, thanks to all for reading the post and for your suggestions.
Electrician found fault and has narrowed it down to a particular length of cable by doing his testing, and eliminating different sections as he went.
The length of cable in question goes from the last socket to the fuse box.
There is a live/earth fault on this cable.
Unfortunately, it is from an extension we had built 10 years ago and the builder buried the cable under the concrete floor without any protection. We lifted carpet, and this was very wet, either because of rising damp or from a burst pipe we had 2 months ago in the bathroom above, that flooded this room.
So, the cable drops from this last socket, goes under the concrete floor and enters original house where it then goes into a junction box. Electrician disconnected at this point and the fault is definitely under the concrete floor somewhere. The cable must be damaged/moisture entering it.
We have 2 options, run a new length of cable from socket to fuse box to make the full circuit, or put the sockets on a radiole. For now we have done the radiole option, using a smaller MCB. I have a seperate downstairs circuit for kitchen anyway and this one is mainly just tv, computers, occasional vacuum. He was at our house in total over 3.5hrs on two seperate occasions and he went out to get the mcb for our particular fusebox. I paid a very fair price for this work(£70.00) and we get a certificate

 

[JohnD]

Price is more than reasonable.

Re-running the cable is IMO preferable as it enables you to have a 32A ring instead of a 20A radial. But some people will say it doesn't matter. If you have two large appliances running at the same time on a 20A radial, it will trip (and might do if you have e.g. a kettle and toaster running at the same time).

If the cable run is only through a single room, one way to deal with it would be to run the cable along the wall, about 450mm above the floor, straight and horizontal, preferably in mini-trunking which is quite neat and can be painted to blend in. This will enable you to put one or more new sockets along the wall on this run, which will probably be useful. Next time the room is going to be decorated, you could have the cable sunk into the wall, plastered over and redecorated. If the cable is going to be concealed, it is important to have two or more sockets along the run, as this gives the clue that there is a cable in the wall, and prompts people to think and check before drilling into the wall there.

 

[ban-all-sheds]

Electrician slightly baffled but he says he will not charge until fault is found, then will only charge for fixing fault. He has worked for our family before.

He was at our house in total over 3.5hrs on two seperate occasions and he went out to get the mcb for our particular fusebox. I paid a very fair price for this work(£70.00) and we get a certificate

Very fair indeed.

I hope you kept him well supplied with tea and biscuits, and that you'll recommend him to others.

 

[ban-all-sheds]

Price is more than reasonable.

[pedantic]Shouldn't that be "less than reasonable"?[/pedantic]

 

[JohnW2]

So, the cable drops from this last socket, goes under the concrete floor and enters original house where it then goes into a junction box. Electrician disconnected at this point and the fault is definitely under the concrete floor somewhere. The cable must be damaged/moisture entering it.

Interesting. Unless there are joints in the cable within the concrete floor (unlikely), I suspect the damage may have been done by some sort of 'movement' in the concrete. Moisture, per se, shouldn't really be a problem - although definitely 'not recommended', undamaged PVC cable is essentially OK even if submerged in water!

However, I'm very glad that the problem has been identified, and at least temporarily solved, and at an exceptionally reasonable price!

Kind Regards, John.

 

[ban-all-sheds]

I phoned electrician and apparently it's a test he always does on a live circuit to measure earth looping, he called it the 'zed S' test.

In case you're curious:

http://www.tlc-direct.co.uk/Book/8.6.2.htm