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 he
http://www.theiet.org/forums/forum/m...nterthrea d=y

--
Andy

Andy Wade wrote:

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 he
http://www.theiet.org/forums/forum/m...nterthrea d=y


lol, weird! Just goes to prove v-ELCBs are better than RCDs

NT

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:

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.

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

Dave

Grimly Curmudgeon wrote:

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

What would you suggest writing on the MCB label?

--
Andy

wrote:

lol, weird! Just goes to prove v-ELCBs are better than RCDs

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.

--
Andy

Andy Wade wrote:
wrote:

lol, weird! Just goes to prove v-ELCBs are better than RCDs

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.

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

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.

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

Andy Wade wrote:
wrote:

lol, weird! Just goes to prove v-ELCBs are better than RCDs

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.

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

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.

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

Andy Wade wrote:

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

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


--
Cheers,

John.

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