Re: I got a shock, and RCD didn't trip...


| 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?
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wrote:

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 !
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Andy Dingley wrote:

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.
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;-)
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.

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

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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
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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

snipped-for-privacy@ntlworld.com
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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

be
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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

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Andrew Gabriel 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
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Succorso Wrote:

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

Some details on tracking down the causes of nuisance trips here:
http://wiki.diyfaq.org.uk/index.php?title=RCD
--
Cheers,

John.

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