From Newsgroup: uk.d-i-y

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?
--
rCLThere are two ways to be fooled. One is to believe what isnrCOt true; the other is to refuse to believe what is true.rCY

rCoSoren Kierkegaard
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From Newsgroup: uk.d-i-y

The Natural Philosopher wrote:

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?

"unclean" sequence of reconnecting individual supply conductors?

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From Newsgroup: uk.d-i-y

On 11/05/2026 16:42, Andy Burns wrote:

The Natural Philosopher wrote:

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?

"unclean" sequence of reconnecting individual supply conductors?

I am only on one 11kV phase....?
--
If I had all the money I've spent on drink...
..I'd spend it on drink.

Sir Henry (at Rawlinson's End)

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From Newsgroup: uk.d-i-y

On 11/05/2026 13:53, The Natural Philosopher wrote:

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?

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)
--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------|
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From Newsgroup: uk.d-i-y

On 11/05/2026 17:37, John Rumm wrote:

On 11/05/2026 13:53, The Natural Philosopher wrote:

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?

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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