Today I experienced an electric shock in my house, after I touched a bare
cable, which I had foolishly left exposed. The cable touched my leg and I
had a heck of a jolt up my body which pushed me out of the way.
I am now wondering why the RCD did not trip. Last year a contactum split
load CU was fitted, the cable which I touched is on the RCD side. Could
there be a problem somewhere, or was the shock I had below the trip current?
| Today I experienced an electric shock in my house, after I touched a bare
| cable, which I had foolishly left exposed. The cable touched my leg and I
| had a heck of a jolt up my body which pushed me out of the way.
| I am now wondering why the RCD did not trip. Last year a contactum split
| load CU was fitted, the cable which I touched is on the RCD side. Could
| there be a problem somewhere, or was the shock I had below the trip current?
| Any ideas?
I'd expect that the shock was probably less than the trip current. If that's a
100mA RCD then
it's hardly surprising.
However, if you're worried re the RCD then best to get it tested. I assume
that you have the
test records from the installation which show that it was working when installed?
Also, you should take more care! Shouldn't really have exposed live conductors
around to touch
and circuits should be isolated (and discharged) before working on them.
Yep !!! This one was your warning, the next one might be worse if you carry
on exposing live cables in easy reach. Always a good idea, especially if
you're going to work on cables that will become live when your testing
others that are connected, is to wrap a piece of insulting tape around them
before you make the circuits live again for your test.
You don't say what exactly you touched. If you contacted bare live and
neutral, then the RCD "sees" you as a normal and legitimate load, and will
not trip. This will only happen if current from either live or neutral finds
an abnormal return path, normally via an earth.
I think you're right, but the great and the good prolly thought we wouldn't
get the idea and try to connect it across earth.
Like Swiss bankers couldn't understand Lsd, so we had to go metric :-(
Earth Leakage Circuit Breaker is generic and covers both types.
RCD is a Current Operated ELCB, whereas the older ones which
monitor the voltage on the CPC verses a ground spike are,
unsurprisingly, called Voltage Operated ELCB's.
The term RCD resulted from Which? and That's Life! suggesting
that the industry adopt a common term, and it needed to be shorter
than "Current Operated ELCB" which Joe Public wouldn't understand.
"Tim Mitchell" wrote
| >The term RCD resulted from Which? and That's Life! suggesting
| >that the industry adopt a common term, and it needed to be shorter
| >than "Current Operated ELCB" which Joe Public wouldn't understand.
I've never really understood what RCD actually means. I know what they do
and how to use them, but Earth Leakage Circuit Breaker does exactly what it
says on the BS EN IP-rated enclosure.
| An interesting bit of history which I didn't know (Esther Rantzen's
| contribution to electrical engineering. Who would have thought it)
Well, she did play a major part in getting open-flued gas heaters (the
infamous Ascot water heaters, my parents always rather liked theirs when
they had one) banned in bathrooms because of the dangers of CO poisoning.
I guess inbetween Esther Rantzen on the one hand, and the nomenclature
police at IEE ("extraneous-exposed-conductive-part" - I ask you!) they
came up with this neutral no-name thang. "Differential" rather than
"residual" might've been a little clearer. "Current Balance Device"
would've been informative, *and* used shorter words. Ah well... no-one
asked me, right? ;-)
| the nomenclature police at IEE ("extraneous-exposed-conductive-part"
| - I ask you!)
I have a sneaky suspicioun they are trying to harmonise us with something
German. More bleedin' hyphens than a Twistleton-FFyffe.
Could have been worse I suppose. Microsoft might have given us "My Grounded
No such thing! There are extraneous-conductive-parts  and there are
exposed-conductive-parts . These are different things, but the twain
_should_ meet in your bathroom, via ... (you know the rest).
 Non-electrical metalwork which may "introduce a potential,
generally earth..." - e.g. metal plumbing & waste pipes.
 Earthed metalwork of electrical appliances - e.g. wall heater,
electric towel rail.
Aye, I do know: and the mumpty that decided on the nomenclature, using
two such similar words, deserves to spend a few thousand years in
purgatory trapped in a late-1980s helpdesk dealing with Expanded vs
Extended memory (come on now! quickly! summarise the differences!) ;-)
Expanded memory was a system where you could set a window under the 1Mb mark
into the expanded memory bank. The window could be moved to expose a
different section of the memory. It was developed to help store additional
information (particularly spreadsheets) that just couldn't be squeezed in.
There was no virtual memory on Intel processors at this time.
Extended memory was simply memory located above the 1Mb mark. This was only
available on 286 processors or above, as previous processors only had a 20
bit address bus. (The 286 has a 24 bit bus, and the 386 a 32 bit one).
Unfortunately, MS-DOS, the operating system of the time, did not allow the
processor to be in the mode required to access this memory, so various
memory extenders were required to switch the processor into and out of the
mode as required. (HIMEM.SYS later helping out with this task).
Expanded memory come first, when pre-286 processors were common and the
640kB limit at its worst. Extended memory took over by the time 386s came
along with their fast context switches (and Windows 386 Enhanced and
DOS4GW). It is far easier to work with and much less limited in size and
performance (and does not require additional hardware).
... with the Intel 'Above Board', IIRC. I remember buying one at work in
1980-something to run a upgrade release of Touchstone (1.4?) on our 12 MHz
'286 PC-AT, with 20 MB HDD! The price for 1 MB ran to 4 figures.
Ah. I remember the old AT with the really expensive EGA graphics upgrade.
That was the third computer I used, after the PDP-11 and the Spectrum. The
PDP-11 was fantastic. I learnt to program on it when I was five. We had two,
sitting in the front room, with the teletypes sitting in the back room. I
remember the excitement when the first VT100 arrived (must have been 1979).
Such modern technology! You can still see the evidence of them now. My
parents still have the holes in the floorboards where all the cables ran.
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