Bizarre reason for RCD nuisance tripping...

Apr 13, 2006 9 Replies
A

While RCD nuisance tripping continues to occupy our minds I thought this piece, posted in the IEE/IET Wiring Regs Web forum this morning might amuse...


The case I was thinking about was a little old lady who lived alone.
> I had rewired the cottage (out in the sticks) and replaced an old
> voltage operated CB with an RCD as part of the works.
>
> Job done, I was alarmed to get a constant series of phone calls from
> the son indicating the RCD had tripped. This happened during the
> night and every time the lady got up the power was off.
>
> It turned out she was in the habit of getting into bed with the
> lights turned off and reaching for her bedside lamp which had no lamp
> in it. In went the fingers - quick jolt and she claimed she felt much
> better. She had done this for years but since the RCD install, off
> went the power. Bedroom was dark so not noticed until the following > am. >
> Not the sort of fault you can predict - and the old lady wasn't
> admitting to her actions - she instinctivley knew it was "wrong" but
> carried on regardless, convinced that it did her heart and
> circulation some good.

Original thread here:

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M

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weird! Just goes to prove v-ELCBs are better than RCDs :)

NT

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G

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Wade saying something like:

In the interests of customer satisfaction he should have run an unprotected spur purely for her bedside lamp.

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A

What would you suggest writing on the MCB label?

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A

Ah, you were right all along... ;-)

Actually though, something about the story doesn't quite ring true, & I'm not sure whether to believe it.

If the bedside lampholder was plastic bodied and/or unearthed, most of the shock current would be phase-neutral. I'd be surprised if there was enough earth leakage to trip a (presumably) 30 mA RCD, unless her bed was rather damp.

If the lampholder was earthed metal, why did the old ELCB not trip?

I suppose that a plastic/unearthed lampholder, replaced with earthed metal after the re-wiring would explain it though.

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G

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Wade saying something like:

The Tingler. or Skull and Crossbones.

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M

thats one option I dont want to think about, Or it may have been a metal frame bed.

Theres not much likelihood touching the pins would trip a voltage operated ELCB. One of those would only trip when so much current flowed that the earth electrode voltage rose up to 25-50v ac. That means quite a lot of current.

Having had enough shocks for one lifetime, I find it hard to belive anyone would do that on purpose day after day. Wasnt on 110 was she?

NT

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M

thats one option I dont want to think about, Or it may have been a metal frame bed.

Theres not much likelihood touching the pins would trip a voltage operated ELCB. One of those would only trip when so much current flowed that the earth electrode voltage rose up to 25-50v ac. That means quite a lot of current.

Having had enough shocks for one lifetime, I find it hard to belive anyone would do that on purpose day after day. Wasnt on 110 was she?

NT

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J

because it ceased to function years ago like many of them!

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