Safety - does switching off at consumer unit isolate the circuit switched?

[Joric1]

I am not an electrician (as you will see from the question!) and I am not planning on doing any electrical alterations. My question is one of safety. I wanted to move a couple of sockets on a kitchen ring main. So I switched off that circuit on the RCD board and all the sockets were then dead. I thought that this isolated the ring main and so was safe to work on? In the process of trying to move one of the sockets I had to take out the wiring and at this point the RCD for the whole downstairs tripped – I was alerted by the lights going off. I thought at first this was a coincidence and a separate fault had developed in the lights! But after turning everything back on except the socket circuit the same thing happened again just when I moved the wires around. My question is, would this be normal for what I thought was a dead circuit to trip the RCD switch? Is there some residual sensitivity to short circuits in a circuit that is switched off? Or when you switch the switch are you not really disconnecting? Is it safe to carry on messing about with the sockets? Is it safe if I switch off the RCD control switch for the downstairs? Or do I have to switch off at the mains? On the other hand is this an actual fault? Should I be calling an electrician? Should I call back the electrician who installed the consumer unit less than a year ago – could it be wired up incorrectly? I have never had any trouble with the sockets when connected, before or after. Please excuse ignorance.

 

[SJD]

Yes this is normal.

When you short N and E on the socket circuit, it provides an alternative path for a small amount of current from other circuits on that RCD, which will often trip the RCD.

It does not indicate anything wrong with the consumer unit install. In fact I'd be worried if it didn't trip (assuming there are other circuits in use at the time).

 

[littlespark]

Rcd’s work in a way that if you touch the live or neutral, it will trip.
turning off a circuit breaker only disconnects the live.

what you possibly did was touch the neutral to the earth wire or earthed backbox, causing the rcd to trip, because it thinks there’s a fault.

 

[Joric1]

Thank you both - replies greatly appreciated. I tried the experiment N to E and that indeed seems to be what did it. That means I can get on and move the sockets ready for tiling tomorrow, with confidence. Although... when you say "small amount of current" I'm assuming you mean not enough to feel it!

 

[littlespark]

The small amount of current is anything up to 30mA. Stated on the Rcd. (Other ratings are possible, but unlikely in domestic)

Different story if you touched a 230v live cable. You would still receive a shock, but only for 40ms or less. Still long enough to feel it.

Both statements here are true, IF the RCD is working properly.