Electrical funny

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wrote:

You won't be, it just feels like it.
-- Smert' spamionam
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On Mon, 22 Sep 2003 10:28:58 +0100, tony sayer wrote:

A whole house RCD should be a 100mA time delayed device. It is there for circuit protection because the earth loop impedance is (or maybe) to high for prospective fault currents to be large enough to trip overload devices within the specified time(s). It is not there for shock protection.

Quite. For that you need a 30mA non-delayed device, even then a belt through one of those hurts. The delayed/non-delayed action is to provide discrimination between the devices, the current rating alone does not guarantee that.
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tony sayer wrote:

I don't. I rely on common sense. ;-)
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No argument there then:-))...
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Tony Sayer


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If I recall correctly, 40mA will kill you, therefore RCD's are set to trip at 30mA
The whole purpose of an RCD is to try to prevent people getting killed from electrocution installing a 100mA breaker, IMO is madness
The only reason I can see to use a 100mA breaker, would be to feed it's output directly into several 30mA breakers to keep a handful of circuits separate (for example, mains in ->100mA breaker, then this feeds to house 30mA breaker and another 30mA breaker for another building.
I had a problem with an old MK ELCB - it would randomly trip for no apparent reason Turns out the breaker was knackered - It was replaced with the same make/model/rating, and it hasn't tripped incorrectly since
Just my 0.02
Sparks...
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So can 30mA, but not normally within the time it takes for an RCD to trip.

No, that's _one_ purpose. Indeed RCD's used for providing protection against electrocution must not exceed 30mA rating. However, RCD's protecting a whole installation (due to excessive earth fault loop impedance) must be at least 100mA, but cannot be used to provide protection against electrocution. Hence a single RCD cannot do both jobs.

A direct swap is indeed silly. The installation was wrong before, and is now wrong in a different (possibly more dangerous) way.

No, that doesn't work. RCD's don't discriminate on current. You should avoid daisy chaining them at all, but if you have to, the one nearer the supply has to be a time delayed type.
100mA and greater RCD's are for protection again high earth impedance, where a short to earth might not pass enough current to trip the fault current protective device within the required time (or even at all). This is commonly the case where the system uses an earth rod for earthing.
--
Andrew Gabriel

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writes:

trip
from
Hmmm, that's interesting.
One of my projects for Q1 next year (ie before the draconian new regs appear and drive the cost up to the point where I won't bother) is to replace my cu rrent CU.
I've read through a number of posts on the matter, and will be getting hold of a 16th edition on-site guide soon, but initial plan was to install an isolator before the CU, and replace the current one with one populated with a mixture of RCBOs and MCBs, possibly splitting my office off onto it's own ring, protected by an MCB due to the amount of computer equipment in there.
I had been uncertain as to whether the CU should have overall protection of a time-delayed 100mA RCD, but from what you say this is probably not necessary nor desireable. The earth is supplied by the provider.
Is this about the size of things?
cheers Richard
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
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wrote:

One thing to be wary of is that the new regulations don't kick in with a retrospective element.
By this I mean that when you eventually come to sell your house the solicitors may wish you, as the seller, to confirm whether there has been any electrical modifications made during your tenancy - and if so to provide appropriate certification. It is already common for the purchasers solicitor to issue a questionaire to the buyers solicitor requesting confirmation of various services, neighbourhood disputes, etc.
This particular question about the electrical installation could be posed a number of ways, I suppose I would not be surprised if they left out mention of 1st April 2004.
PoP
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appear
cu
Yup, noted, thanks.
It should be said that there are also quite a number of ways to answer a question truthfully...
cheers Richard
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
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wrote:

I spy a budding politician and claim my five pounds ;)
PoP
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Public life? I think not! :-)
Just spent rather too much time (and money) in the company of lawyers recently.... think some of it must have rubbed off. I obviously need rehab...
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
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On Sat, 20 Sep 2003 20:08:00 +0100, Adrian Simpson

No, chances are that it's a voltage-activated RCD. Is it old ? 15-20 years ? These things were a bit prone to this problem.
-- Blind drunk - Please ignore all postings I make, until I sober up enough to notice the .sig file that has been attached to them. Thank you.
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