RCD Fault

[Bright.Spark]

Ive just got back from a nightmare fault. an electrician rewired a customers kitchen, which was done around 2 weeks ago. Today the customer turned on his extractor for the first time and it tripped his RCD. I was called to investigate and found it to be an earth on the kitchen sockets, when it touched the earth bar with the cable, it tripped the RCD. Just as I split the ring, the kitchen electrician turned up and didnt want me to continue. I left not to cause bad feelings and he later rang me and said the problem is on the upstairs lights not the kitchen sockets, he said the earths was in the wrong place and it was the upstairs lighting earth we had out not the kitchen sockets earth. The thing that is confusing me is the board is an old split load one where there is only 1 RCD on it covering the sockets. The upstairs lighting circuit isnt protected by an RCD. My understanding was if a circuit isnt protected by an RCD it wont trip the device. Any ideas?

Also the customer has 15 LV lights upstairs, could a possible faulty transformer causing the problem???

 

[Draig Coch]

Hi BrightSpark just running through this for a second. Are the Kitchen SO on a ring? If so were there 2 x 1.5mm earths that you were removing? Secondly if it was the extractor fan that was faulty he most likely took the feed from the down stairs lights no? Or was there a fused spur from the kitchen SO?

 

[Bright.Spark]

There was two 1.5 earths in the terminal at the fuse board. The kitchen sockets are in a ring. He reckons he spurred off the sockets for the extractor which is on a plug top.

 

[Draig Coch]

I see, for what its worth I have heard of unusual behaviour of RCDs from unrelated circuits so without going through the install yourself circuit by circuit we are left to best guess.

As the RCD was only on the ring the device was tripping through an in-balance in L&N. By making the earth connection (providing the return path for the fault on the ring) you tripped the device.

On the face of it the ring circuit is as guilty as a fox in a hen house and the guy was covering his tracks. I'd have liked to see IR (L&N to E) results of the ring with the extractor fan in and out of circuit.

 

[IQ Electrical]

I see, for what its worth I have heard of unusual behaviour of RCDs from unrelated circuits so without going through the install yourself circuit by circuit we are left to best guess.

As the RCD was only on the ring the device was tripping through an in-balance in L&N. By making the earth connection (providing the return path for the fault on the ring) you tripped the device.

On the face of it the ring circuit is as guilty as a fox in a hen house and the guy was covering his tracks. I'd have liked to see IR (L&N to E) results of the ring with the extractor fan in and out of circuit.

I agree, there was almost certainly a fault on the ring, why was the original installer not asked to correct the problem immediately on such a new installation?

 

[telectrix]

agree with IQ. probably the guy has had to fix the fault for free, so has invented a fault on the upstairs lights so as to be able to charge.

 

[Richard Burns]

Is this not just a case of a faulty extractor. If you check the extractor socket is correctly wired (no borrowed neutrals as well) then with the extractor unplugged see if the earth connection on the ring trips the RCD, if it does not trip then it is just the wiring in the extractor you need to check (unless there is a fault inside the extractor)

 

[IQ Electrical]

Is this not just a case of a faulty extractor. If you check the extractor socket is correctly wired (no borrowed neutrals as well) then with the extractor unplugged see if the earth connection on the ring trips the RCD, if it does not trip then it is just the wiring in the extractor you need to check (unless there is a fault inside the extractor)

I would have thought that the 'kitchen electrician' would have been quite happy to blame a faulty extract fan?

Why blame the upstairs lighting?

 

[truckster]

If the install was two weeks old and the first time the fan was turned on there was a problem I would be fairly confident it was a problem with the fan or its wiring, as been said, fairy fault to cover his tracks.

 

[Bright.Spark]

rite I went to the job quickley today. I firstly did a continuity check between earth and neutral and got 10 ohms. I then did a N-E test on the upstairs lights and got 2.87 ohms. Whats peoples view on this? Finally i just went for it and connected the earth which was the problem to the earth bar and the RCD didnt trip. I turned all the lights on and had no problem. Any ideas??? Im just confused why an upstairs lighting circuit which isnt protected by an RCD would trip an RCD.

 

[telectrix]

did you have the N and E dissed from the CU when you got the 2.87ohms? still think the fault was on the extract fan and he made up the lighting fault . anyway, why did he not fix the obvious fault on the lights?

 

[Des 56]

Finally i just went for it and connected the earth which was the problem to the earth bar and the RCD didnt trip

I'm getting a little lost with this thread
Can you expand on this statement please.

 

[Deleted member 9648]

Some very odd test /fault finding proceedures going on here....:saddam:

 

[Bright.Spark]

Yep the neutral and earth was disconnected from the board when i tested.

Sorry for it being confusing, I was called to a job last friday a customer said he turned on his extractor fan in his kitchen and it tripped his RCD. His kitchen has just been fitted and it was the first time he did this. I started testing and the electrician who did the kitchen turned up and swore it wasnt his wiring.

Monday I got a phone call from the electrician saying it is a problem with the upstairs lights not the kitchen sockets and that every time he put the earth of the upstairs lights on it tripped the RCD. The thing is the lights are not protected by and RCD, its an old 16th edition board where RCD is just for the sockets. Today I tested the board and between neutral and earth bars I got 10 ohms. I then disconnected the earth and neutral of the lighting circuit and got 2.87 ohms. I reconnected the earth to the upstairs lights (which the kitchen fitter said was to be the problem) and nothing has tripped. I turned all the lights on and nothing tripped. Any ideas????

 

[Des 56]

It would appear that there is a fault with the upstairs lighting to have such a low n-e insulation resistance reading and should be investigated

That low reading should have no impact on the function of the rcd as you state, considering you have a non rcd side for the lighting circuit
Was the insulation resistance test carried out with all precautions taken, or was this done on the continuity range with appliances in situ
Its still vague to me what actual tests were carried out and were they carried out as per should have been

Little porkies may be being told, and a fault that was causing the problem has been rectified with a
"it was nought to do with me guv" rear end covering