RCD tripping even with all MCB's off when it was a LINE to earth fault.

[Lawmal]

Hi, can anyone please explain this situation. 30mA rcd was tripping in a domestic installation. I narrowed it down to a lighting circuit but even with all McB's off, the rcd kept tripping, so I naturally imagined that it mus be a neutral to earth fault. In fact i discovered the problem and it was a clearly visible LINE to earth fault. Why was the RCD tripping even with all mcb's off when it was a line to earth fault?? The RCD was only tripping if the bulb was in the luminare, when I removed the bulb the Rcd only tripped when the Mcb was on and the fixture lighting turned on as naturally it does when it is a line to earth fault. But when the bulb was in the affected luminare the rcd kept tripping with all mcb's off!!

 

[davesparks]

The lamp connects line to neutral

 

[Lawmal]

Perfectly right, thanks !!! must have been really tired not to have figured it out!!