One of my recent projects I have been working on is a variac (variable mains autotransformer), in a nice project box with meters.
I've finished the mechanical side of the build, and wired everything up yesterday.
The setup:
This all works well, and everything seems to function as it should. However - when I press the 'test' button on the RCB on the project, two things happen.
1) - The RCB on the project flicks off (as you would expect)
2) - The RCB in the main fusebox that feeds my workshop also flicks off
This seems a bit weird - as from what I can tell, the test button just allows a small amount of current to bypass the toroid inside the RCD being tested. The fact that the whole workshop is tripping indicates it is actually allowing the test current to flow from live to neutral - this seems a bit weird.
I've found the main RCD covering the workshop to be very sensitive - once I cut through a mains cable (with live switched off at the breaker) - the act of the cutter shorting earth and neutral was enough to trip the RCD. This seems to indicate my neutral is slightly above earth potential?
Any thoughts would be very helpful!
Cheers,
Andy