We had a power cut here a few days ago ('Grounded 11KV overhead line' - presumably branch etc) and power was restored after about 6 hours. On restoration my RCD (100 mA whole house) tripped instantly.
I reset it, and all was normal.
Anyone know why?
Curious behaviour of RCD/Main trip
May 11, 2026
Last reply: 2 months ago
4 Replies
"unclean" sequence of reconnecting individual supply conductors?
I am only on one 11kV phase....?
Lots of SMPSUs with input filters?
The sharp transient at switch on can dump excess current to earth via those, which could look like excess leakage. If you are already have relatively high leakage to sensitise the RCD, that can be enough.
(also luck of the draw as to where in the mains cycle the "switch" was closed)
If we have a power cut, (and we're in) the first thing I do is to kill all the breakers on the CU, except a lighting circuit, and use the lamp(s) on that to know when the power is restored. Even when it is, I wait a minute of two, before slowly restoring the other breakers one by one.
If we're, well anything might happen, but hey !
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