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There must be larger hole in my knowledge than I appreciated, as I can't get my head around why both the mcb and rcd should trip on short to earth.
Situation was wasa taking quick peek into a live double socket to check which way ring ran out the back of the dry wall box. About to push it back when thought - I know, I'll just check the terminals are nice and tight first...
Somehow, shorted live to the socket earth strap. Still don't know how, as I was using proper VDE driver with insulation to within couple of mil of tip, and terminal connector deep and well shielded.
Anyhow - VDE screwdriver, MCB and the RCD (17th ed CU) all did their jobs - just a flash and a slightly shorter screwdriver tip...
What I don't get is why the MCB tripped - or more precisely, had time to trip. Assuming the 30mA 63A RCD in the CU is within spec, it should see the L-N imbalance in around 18mS. So wouldn't it kill the power before the MCB could trip - ~ 18 mS being shorter than 0.4 seconds?
What am I missing or misunderstanding here please ...
Situation was wasa taking quick peek into a live double socket to check which way ring ran out the back of the dry wall box. About to push it back when thought - I know, I'll just check the terminals are nice and tight first...
Somehow, shorted live to the socket earth strap. Still don't know how, as I was using proper VDE driver with insulation to within couple of mil of tip, and terminal connector deep and well shielded.
Anyhow - VDE screwdriver, MCB and the RCD (17th ed CU) all did their jobs - just a flash and a slightly shorter screwdriver tip...
What I don't get is why the MCB tripped - or more precisely, had time to trip. Assuming the 30mA 63A RCD in the CU is within spec, it should see the L-N imbalance in around 18mS. So wouldn't it kill the power before the MCB could trip - ~ 18 mS being shorter than 0.4 seconds?
What am I missing or misunderstanding here please ...