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YAPH YAPH is offline
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Default MCB tripping - why?

On Tue, 29 Dec 2009 02:41:08 -0800, nafuk wrote:

Hi, the MCB on my split circuit consumer unit is tripping sporadically,
sometimes when nothing is connected to the downstairs socket circuit.
The MCB protects the RCD protected circuits (upstairs and downstairs
sockets, cooker, hot tank, kitchen sockets). The hot tank and cooker
circuits are turned off at the rcd and are not connected used/connected
yet.The light (non-RCD'd) circuits stay on when the RCD trips.


Some confusion he one generally has an RCD giving residual-current
protection to one or more MCB-protected circuits, not the other way round.
Please can you confirm your layout of MCBs and RCDs?

(The RCD is the one with the 'TEST' button.)

Please can someone tell me what causes an MCB to trip, other than
overcurrent, and not trip an RCD, and hopefully some possible things to
check in order to locate the fault.


Overcurrent is the only thing that causes an MCB to trip. A difference in
current between live and neutral causes an RCD to trip. Thus a fault that
causes excess current to flow (slightly excess for a long period or gross
excess for a short period) trips an MCB (or other over-current device
such as a fuse). A few tens of milliamps leakage to earth trips an RCD -
even touching neutral and earth together on a circuit switched off at the
MCB or other single-pole switch in the circuit can cause enough earth-
loop current to flow to do it.


--
John Stumbles -- http://yaph.co.uk

Xenophobia? Sounds a bit foreign to me.