Odd voltage on Off peak circuit

[Dartlec]

While sorting out some issues with immersions at a flat yesterday, I ran into something that seemed peculiar (to me at least).

Immersions need new thermostats/cut out, all quite normal..

However, while testing the lower (off peak) immersion I was getting 13V L-N - which I assumed was just my meter picking up 'stray' voltage from wires running together.

However, when testing resistance across the immersion, the off peak RCD tripped.... (Possibly when also touching earth).

After resetting it I checked again and no voltage at all showing up on the off peak - and RCD test button non responsive as expected since it was not an off peak time....

I imagine the neutral is shared between on peak and off peak boards, though didn't take them apart to verify. But could that give a situation with a stray current where the RCD was 'powered' adequately to trip?

Boards are fairly recent, with Wylex RCD protection - on a flat with economy 7. I did verify the polarity of the main incoming supply at the other immersion switch since a meter had recently been changed.... Didn't have time to investigate any further though...

Is it normal to get a situation where you can trip the off peak RCD even when Line isn't powered? Not something I've run into before...

 

[Lucien Nunes]

Yes. A conventional non-electronic RCD doesn't need to be 'powered', the tripping coil is operated directly from the balance transformer. Completing a circuit N-E can cause a residual current regardless of whether the line is present. One should preferably isolate all poles when carrying out resistance tests.