12VAC on circuit.

[Stripestripe]

I've had boiler changed from condenser to combi so water tank removed from airing cupboard. Immersion heater switch was left in in situ but "load" cabling removed back to switch and circuit switched off at the 16A mcb.

Wanting to put a WiFi repeater in the airing cupboard I thought I'd replace the switch with a socket and reactivate the circuit.

Now the funny stuff - with the MCB pulled, there's 12VAC on the circuit (?). Tested with multimeter. Engage the MCB and 240VAC appears as expected.

Pulled the MCB to make the change. As I removed the immersion switch the RCD tripped(?)

The sockets, cooker and hob MCBs are on the same RCD.

Any ideas? Where's the 12VAC coming from?

 

[DetlefSchmitz]

The voltage is capacitive coupling. Multimeters are too high impedance for this kind of work. The RCD tripped because you allowed the earth to touch the neutral.

 

[ban-all-sheds]

I thought I'd replace the switch with a socket and reactivate the circuit.

The problem is that you won't have been able to do any testing....

 

[Stripestripe]

The problem is that you won't have been able to do any testing....

The immersion heater has just been removed - what testing do you mean please?