please help !!! RCD Poblem

cyberjunction · Mar 14, 2011

Hi

I am doing my first consumer unit for my assesment on Friday and have come a cropper.

I have put in a split dual consumer unit, Wylex.

On the one half, closest to the main switch, the rcd works fine.
The second RCD, the test button does not work . When I apply a load ie upstairs kights , it trips straight away.Obviously thought the RCD was faulty so took it back and got it replaced and the same problem. I have disconnected all lines form the MCB and the buzz bar but the same problem. I have ensured there is no connection between the neutrals on the neutral bars as some one suggested and am completely stuck,

Can anyone help, I am panicking with my assesment due and am hoping this is something silly.

Just a note there is voltage to the RCD.

the preivous consumer unit was a single rcd and MCDs with problems

Thanks

pushrod · Mar 16, 2011

alanl said:
Neutral to earth fault.
Even if the MCB for the faulty circuit is off, the RCD will trip. It will not reset, so the test button will not work.

How does that work then

Is that because there is some earth leakage elsewhere that is choosing to go through the neutral of the rcd rather than through the main earth? Would that be more likely on a TNS or TT (as opposed to a TNCS) where the return impedance of the N would be less than that of the earth?

tony mc · Mar 16, 2011

I maybe read it wrong.

Did't he say the RCD test button would not work when energised then after a while the RCD tripped.

Thats what has caused the concern I think.

The second RCD, the test button does not work . When I apply a load ie upstairs kights , it trips straight away

I can see what alanl is saying but thats not the case here the RCD is already energised but will not trip.

pushrod · Mar 16, 2011

tony mc said:
I can see what alanl is saying but thats not the case here the RCD is already energised but will not trip.

There was a case the other day (if i remember correctly) where someone was saying that their rcd was tripping even though the lines were removed from the mcbs was just wondering what is going on. You normally think that the circuit would be energised for the rcd to work, but seems like it is not in these cases.

Think Alan was saying that with a N/E fault and no power to faulty circuit rcd still can't be reset.

Deleted member 9648 · Mar 16, 2011

I was under the impression that the RCD was energised but would not trip on the test button.....and after disconnecting the faulty cooker circuit the test button worked....maybe I've got that wrong,if not I cant see how disconnecting a faulty circuit could affect the test button.

cyberjunction · Mar 16, 2011

final update - cooker problem solved

the cable form the cooker to cooker point was sliced very slightly. Its seems when the gas fitter fitted, he had pushed the cooker back and nipped the wire, the cable was about 3 foot too long so cut and reconnected and all is sweet, rcd does not trip and the missus is cooking agian
thanks again for everyone help, I hate being new to something and not knowing !!