DIY Doctor


Postby pm1 » Thu Dec 13, 2007 9:28 pm

I have installed a new lighting circuit using junction boxes as all lighting is non standard, spots etc.I have followed a standard wiring diagram which is straight forward. However, everytime I put power into circuit the RCB trips. I have no experience of RCB's. The consumer unit is a split one and the lightiong circuit is on the non RCB side yet it still trips. Thinking I had wired something wrong I reduced the circuit to a single room.Cable from consumer unit to junction box, switch to junction box and light fitting to junction box and everything else disconnected. It still trips. Help please.

December 13, 2007

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Simply Build It

Postby stevenc1603 » Fri Dec 14, 2007 3:41 pm

How have you wired the junction box?

In your single room example you should have the following.

Firstly you need a 4 way junction box. One set of terminals for the lives, 1 for the neutrals, one for the earths and the last for the switched live.

Taking your single cable from the CU, the live goes to one set of terminals, then neutral to another and the earth to a third.

Taking your cable to the switch, attach the live to the same terminal block as the other live.
Attach the earth to the same terminal as the other earth.
Attach the switched live (what will be the neutral of the switch cable that should be tagged to show its a live) to the unused 4th terminal.
Finally the cable that goes to the light. Wire its live to the terminal with the switched live. Wire its neutral to the neutral terminal used for the supply cable.

Now test and see what's happening.

If its all working then attach the supply cable to the next light to the same live, neutral and earth terminals as the supply cable from the CU.

You will need to check this with every junction box until you have it all working.

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Postby kuzz » Fri Dec 14, 2007 8:17 pm

If it is on the non rcd side it shouldn't trip. If you have connected in to the fuse board check you have connected the neutral to the non rcd neutral. If you have the wrong neutral it would trip when energized.
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