Working on a circuit with an RCD board

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Hi, I had to replace a PIR security light for my nans garage at the weekend. I isolated the circuit via the sub board in the garage so the circuit I was working on was dead (I proved this out prior to starting). However during the process of unwiring the old security light and wiring in the new light the RCD in the house tripped a number of times (split board CCU).

This still occurred even when I switched the MCB off for the sub board at the main CCU in the house. I have spoken to others who have advised of similar issues of RCD tripping when working on isolated ring final circuits in houses.

My question is, "Is there a common practice used other than complete isolation of the CCU to stop this occurring"

Thanks
 
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The trip occours when the earth and neutral touch together.

You could have turned off the main switch/rcd at the garage which would be a dual pole isolator.
 
Thanks, in response to other issues I am aware of i.e working on on a Ring Final which is RCD protected, in order to stop this tripping out would it mean the whole board would need isolating via the main switch. Is this the usual practice, or would the L/N/E for the circuit be broken out from the board for the duration of works?

Just wondered on the best approach.
 
depends.

If the other circuits are essential to remain on, then you could disconnect the neutral at the CU.
No need to disconnect the earth.

or work carefully, trying not to touch N and E together.
 
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If you want to achieve isolation you should use the main switch rather than a circuit breaker. In a domestic premises and TT installations ALL live conductors must be interrupted.
 
Timely quesion - I am about to update my lighting circuits and tripped the RCD - despite the MCB being open. Scared the life out of me at first - the clunk followed by my microwave beeping (it lets out a death yelp when it's power is cut!)

I would quite like the rest of the circuits to be live as I'm fed-up of resetting every clock and timer every time I do any work.

Seems like removing the lighting's neutral from the CU will resolve that.
 
You'll need to isolate the entire consumer unit before you remove the cover or carry out any work in it, so your clocks are going to need resetting either way.
 
You'll need to isolate the entire consumer unit before you remove the cover or carry out any work in it, so your clocks are going to need resetting either way.

Good point! Looks like I'll just isolate the whole lot..

Just to confirm my belief - if I switch the RCD (i.e. the one with the test switch) - that *should* make the circuit safe to work on in terms of cutting wires and installing junction boxes?

I will of course test the links are dead before starting.

whitling2k
 
If you want to achieve isolation you should use the main switch rather than a circuit breaker. In a domestic premises and TT installations ALL live conductors must be interrupted.
UK Regs allow you to have the line only disconnected in TN installations.
 
Thanks for this, dependent on the work Im doing I may take the approach of isolating the circuit in question and temp cap the neutral (choc block on the end) to prevent the earth and the neutral making contact. Hopefully that should do it.
 

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