New Consumer Unit - how to isolate circuit?

[IngeJones]

After many years of successfully doing most of my own electrical work I suddenly feel disempowered. With my old consumer unit I only needed to press the button (or remove the fuse) that was directly on the circuit I needed to work on.

With this new RCD one, I flipped the switch on the MCB for the circuit, removed the light fitting I was planning to replace, and when the neutral and live wires incidentally touched each other in the process, the RCD covering that group of MCBs reacted. I take this to imply I had not isolated the lighting circuit properly?

So now I have this new consumer unit, how should I proceed with isolating a circuit other than turning off at the main bipole switch to the entire unit - which I'd really prefer not to do as then I cannot use any power tools I might have been planning to.

 

[ricicle]

It is not unusual for a RCD to operate with only the line isolated as shorting the neutral and earth can cause it to trip due to diverting neutral currents from other circuits still energised.
If you are taking on minor electrical jobs you ideally need an approved volatge tester if you are in any doubt about circuit isolation.

Incidentally - did you get and certification for your new CU ?

 

[DetlefSchmitz]

It was probably the neutral and earth wires which touched to trip the RCD. So it's safe but you have to take care that neutral doesn't touch earth. Temporary use of tape is a solution.

Edit: Someone else on their lunchbreak.

 

[ban-all-sheds]

I take this to imply I had not isolated the lighting circuit properly?

Technically you had not, and never have been - Neutral is considered to be a live conductor, and should be isolated.

So now I have this new consumer unit, how should I proceed with isolating a circuit other than turning off at the main bipole switch to the entire unit - which I'd really prefer not to do as then I cannot use any power tools I might have been planning to.

You only have to turn off the MCB covering that circuit, not the whole CU.

Rubbish.

You only need to turn off the RCD covering that circuit, not the whole CU.

Failing that open it up and remove the neutral from the bar. Or be more careful

 

[ban-all-sheds]

... it's safe ...

Unless there's a borrowed neutral.

 

[IngeJones]

Ricicle, yes the consumer unit itself was fitted professionally and the work was certified. I guess the RCD, being sensitive, objected to something I have been happily doing all this time. Ok, I'll just take care in future to test each wires before starting work and not let the neutral and earth touch. Thanks everyone

 

[ban-all-sheds]

When you connect N & E the RCD is doing what it says on the tin...

 

[OwainDIYer]

I take this to imply I had not isolated the lighting circuit properly?

Technically you had not, and never have been - Neutral is considered to be a live conductor, and should be isolated. ...
You only have to turn off the MCB covering that circuit, not the whole CU.

ITYM RCD (assuming the RCD is double pole switching)

 

[ban-all-sheds]

Oh poo.

Sorry.

I'll change it to avoid confusing anybody who doesn't read all the thread.


Thanks for spotting it.