Electrical puzzlement #2

  jack 09:23 18 Aug 2009

First a thank you to those responses on
click here
with all the word on latest regs., etc.,- my man with his meter sourced a safe earth and all is in and well.
Here is the latest - this time not me but a nieneighbour who rang my door bell on Saturday afternoon last to ask if I has a supply- 'Yup' I responded flicking a sswitch prove it.
'I have been off since noon nothing at all- I thought it may be a repeat of last month' she said.[Four days off due to vandals/cable thieves]
I offered to take a look see.
Sure enough not power at at -except for a mains powered light in the meter cupboard- It is a modern setup consumer unit with 4 breakers.
all four were 'in'[active] but still no power except to the one light.
I turned off the main switch- light went out- turned it on - light came on- tripped each breaker and reset in turn - still nothing.
Me baffled- nothing for it but to call an expert- fortunately- she has cover - within the hour the man in the van turned up-20 minutes later he left with all working.
The lady came to by to thank me and explain the outcome.
It seems in addition to the main CU there is another with a single breaker. This had tripped.
Seeing this He immediately made his way to the kitchen and tested each appliance - Washers etc., until he got to the kettle- thats the culprit he said - unplugged it - reset the the breaker - all back on.
Here is my puzzlement
Presumably the single unit protected the kitchen heavies-
When the kettle failed why did it not blow its own plug fuse?
When that breaker tripped [because of the kettle] why did everything else in the house shut down that is on the 4 breaker unit

This is for information only just to satisfy my ignorance

  oresome 09:36 18 Aug 2009

I suspect there was a RCD fitted.

These trip with currents of 30 mA or less and acted quicker than the dedicated circuit overload breaker.

  crosstrainer 09:41 18 Aug 2009

It was the main RCD in the cupboard. (maybe outside of the property?) Either way, you did the right thing.

  ex-wirecutter 09:58 18 Aug 2009

Nobody appears to have mentioned that in addition to dead shorts RCD's detect slight trickle voltages between earth an neutral . ( which a normal circuit breaker would not react to )

  crosstrainer 10:03 18 Aug 2009


  jack 10:57 18 Aug 2009

Clever that- that independent light in the cupboard.

  wiz-king 11:44 18 Aug 2009

I have a 13A socket on a separate circuit breaker direct from the meter, this normally has an emergency rechargeable lamp plugged in to it. Very useful.

  BT 17:03 18 Aug 2009

Reminds me of the time when I lived in a flat in London and one evening the doorbell rang and there was the very beautiful blonde who lived next door. She asked if the gas was off as her boiler wouldn't work. I explained that for safety reasons it was very unlikely that the gas was off and that ours was OK, and had a look at her boiler for her. It just wasn't firing up at all and was pretty ancient so I had to tell her that she probably need a new one.

  Bingalau 17:12 18 Aug 2009

That story petered out a bit didn't it?

  crosstrainer 17:14 18 Aug 2009

:))!! I guess they missed it.

  Spark6 23:38 18 Aug 2009

One of the most difficult faults to trace and correct are neutral/earth faults on lighting circuits wrongly protected by RCD's. I would hazard a guess that jack's mystery light was not. The number of times I have been called on by householders, in the evening with no lighting, made me realise the importance of 'split boards'.

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