"Succorso" wrote in message
...
| Hi,
|
| I was rooting around under the floor yesterday, sorting out some of the
| previous owners' disasters in the wiring department. At one point, I
| happened to grab a 5A cable, and at the same time touched a 15mm pipe
| carrying the mains water, with the back of the same hand. Pooffff... I
| ended up the other side of the room with a very wobbly arm!!
|
| Turns out, there was mouse damage on the cable which had exposed live
| copper (outer casing and red insulation had been chewed through).
|
| My question is this. Assuming I made a Live - Earth circuit when I
| touched the cable and pipe, why didn't the 100MA trip RCD on the
| consumer unit trip? Could it be that the earthing is inadequate on the
| under-floor copper?
|
| Regards
|
| --
| Chris
|

Hi Chris

Sounds nasty.

Why did the RCD not trip? I would expect that there could be several reasons for this...
- the current flow did not reach 100mA so the RCD did not "see" the fault
- the RCD may itself be faulty - has it been tested recently?
- remember that an RCD does not know in any sense where the residual current goes, it only know
that there is an imbalance (in this case 100mA) in the phase / netural currents. It could be
that the earthing is inadequate, but this failure to trip is not the determinant of that. I
suggest that you measure the earth loop impdence of the circuits in question, to determine
whether the earthing is adequate.
- consider turning off supplies not essential to your work in restricted areas. You were
lucky - how would anyone get to you if you had had a more serious shock?

On Sun, 03 Aug 2003 09:54:24 +0100, Succorso
wrote:

My question is this. Assuming I made a Live - Earth circuit when I
touched the cable and pipe, why didn't the 100MA trip RCD on the
consumer unit trip?

100mA RCDs are there to protect you against overnight fires caused by
mouse damage. If you're expecting to touch a phase conductor (i.e.
sockets on a workbench) then use 30mA. Even then, 30mA is enough to
give you a considerable jolt without tripping.

Check the RCD, check the earthing, but you might just have been
unlucky enough to pass only 99mA, which still hurts !

Andy Dingley wrote:
On Sun, 03 Aug 2003 09:54:24 +0100, Succorso
wrote:

My question is this. Assuming I made a Live - Earth circuit when I
touched the cable and pipe, why didn't the 100MA trip RCD on the
consumer unit trip?

100mA RCDs are there to protect you against overnight fires caused by
mouse damage. If you're expecting to touch a phase conductor (i.e.
sockets on a workbench) then use 30mA. Even then, 30mA is enough to
give you a considerable jolt without tripping.

Check the RCD, check the earthing, but you might just have been
unlucky enough to pass only 99mA, which still hurts !


http://www.memonline.com/rcd3.html shows a current against time graph
showing the effects on a person of shocks. It is for MEM RCDs but based
on an IEC publication.

In article ,
Andy Dingley writes:
On Sun, 03 Aug 2003 09:54:24 +0100, Succorso
wrote:

My question is this. Assuming I made a Live - Earth circuit when I
touched the cable and pipe, why didn't the 100MA trip RCD on the
consumer unit trip?

100mA RCDs are there to protect you against overnight fires caused by
mouse damage.

;-)

Actually, it's there to protect against live to earth short circuit
when the earth impedance is too high to guarantee enough current
would flow to blow the fuse/MCB. It isn't there to protect against
electrocution.

If you're expecting to touch a phase conductor (i.e.
sockets on a workbench) then use 30mA. Even then, 30mA is enough to
give you a considerable jolt without tripping.

Check the RCD, check the earthing, but you might just have been
unlucky enough to pass only 99mA, which still hurts !

Chances are that far less 100mA, and probably less than 30mA
flowed through you.

--
Andrew Gabriel

"Succorso" wrote in message
...
Hi,

I was rooting around under the floor yesterday, sorting out some of the
previous owners' disasters in the wiring department. At one point, I
happened to grab a 5A cable, and at the same time touched a 15mm pipe
carrying the mains water, with the back of the same hand. Pooffff... I
ended up the other side of the room with a very wobbly arm!!

Turns out, there was mouse damage on the cable which had exposed live
copper (outer casing and red insulation had been chewed through).

My question is this. Assuming I made a Live - Earth circuit when I
touched the cable and pipe, why didn't the 100MA trip RCD on the
consumer unit trip? Could it be that the earthing is inadequate on the
under-floor copper?

Regards

--
Chris

or maybe the circuit that you came into contact with was not protected by
rcd, i.e. split load consumer unit. with some circuits not protected. also
it is recommended practice to use a 30mA rcd in domestic premises.
bob

"crooksie" wrote in message
...

"Succorso" wrote in message
...
Hi,

I was rooting around under the floor yesterday, sorting out some of the
previous owners' disasters in the wiring department. At one point, I
happened to grab a 5A cable, and at the same time touched a 15mm pipe
carrying the mains water, with the back of the same hand. Pooffff... I
ended up the other side of the room with a very wobbly arm!!

Turns out, there was mouse damage on the cable which had exposed live
copper (outer casing and red insulation had been chewed through).

My question is this. Assuming I made a Live - Earth circuit when I
touched the cable and pipe, why didn't the 100MA trip RCD on the
consumer unit trip? Could it be that the earthing is inadequate on the
under-floor copper?

Regards

--
Chris

or maybe the circuit that you came into contact with was not protected by
rcd, i.e. split load consumer unit. with some circuits not protected. also
it is recommended practice to use a 30mA rcd in domestic premises.
bob




Find out who fitted the RCD and 'expose' him. Domestic supplies protected be
by an RCDat no more than 30mA - or 10mA on a workbench supply with
electronic equipment.


--
Woody

Supplies to ringmains and other socket outlets need to be protected by a
30mA RCD the regulations specifically state that a 30mA RCD should not be
relied on for whole house protection and that a 100mA RCD with time delay
should be used on TT systems as the main switch and that all socket outlets
must be protected by a 30mA RCD be that as a main RCD in a split board or as
RCBOs. as regards any TN-S or TN-CS systems there is no requirement for RCD
protection Except for equipment likely to be used outside of the
installation.

LOZ



Find out who fitted the RCD and 'expose' him. Domestic supplies protected
be
by an RCDat no more than 30mA - or 10mA on a workbench supply with
electronic equipment.


--
Woody

In article ,
"harrogate" writes:

Find out who fitted the RCD and 'expose' him. Domestic supplies protected be
by an RCDat no more than 30mA - or 10mA on a workbench supply with
electronic equipment.

Wrong.
If this is a whole house RCD, it has to be at least 100mA.
A 30mA one would be against the regs.
If the original poster is refering to a lighting circuit,
that really shouldn't be on a 30mA RCD anyway.

--
Andrew Gabriel

Andrew Gabriel wrote:

In article ,
"harrogate" writes:

Find out who fitted the RCD and 'expose' him. Domestic supplies protected be
by an RCDat no more than 30mA - or 10mA on a workbench supply with
electronic equipment.


Wrong.
If this is a whole house RCD, it has to be at least 100mA.
A 30mA one would be against the regs.
If the original poster is refering to a lighting circuit,
that really shouldn't be on a 30mA RCD anyway.


It's a whole house RCD. We tried a 30mA unit for a while, but it tripped
several times a day so we reverted to 100mA.

Of course, maybe I should have pulled the house apart to find the cause
of the tripping - but it's a big house and we have a lot of stuff, so
going back to 100mA was the easier option.

Regards
Chris

I would have fitted a 30mA RCD just to supply the ring main, leaving the 100mA to protect the rest of the house as well. BS 7671 requires that a 30mA is fitted where a socket supplies equipment outside the Equipotential zone ( Outside of the house). If the 30mA RCD still trips out several times a day then I would be tempted to investigate further but this would require an insulation tester.

Alex Trician wrote:
Succorso Wrote:

It's a whole house RCD. We tried a 30mA unit for a while, but it
tripped
several times a day so we reverted to 100mA.

Of course, maybe I should have pulled the house apart to find the
cause
of the tripping - but it's a big house and we have a lot of stuff, so
going back to 100mA was the easier option.

Regards
Chris

I would have fitted a 30mA RCD just to supply the ring main, leaving
the 100mA to protect the rest of the house as well. BS 7671 requires
that a 30mA is fitted where a socket supplies equipment outside the
Equipotential zone ( Outside of the house). If the 30mA RCD still trips
out several times a day then I would be tempted to investigate further
but this would require an insulation tester.

Some details on tracking down the causes of nuisance trips he

http://wiki.diyfaq.org.uk/index.php?title=RCD



--
Cheers,

John.

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