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#133436 - 08/04/02 05:50 PM RCD behaviuor
ChrisO Offline
Member

Registered: 07/31/02
Posts: 22
Loc: St Ives, Cornwall, UK
Hello everybody

Incoming sub main - breakers open
RCD on out side only neutral connected
outgoing MCB open
NO LIVE COPNNECTIONS AT ALL
RCD won't hold in

it just sits their with (effectivly) one wire in it and won't latch

runs fine on the bench

What I'm trying to run may never work with an RCD (many SMPS) but it puzzles me that the RCD won't latch even with the live not present

The RCD is Farnell's finest - supposed to tolerate anything.

What bugs me most is that the RCDs I expected to have trouble with in wet areas all work flawlessly, this one just supplies a 32A ring main (at 18A) which has passed Inspection

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#133437 - 08/05/02 02:33 AM Re: RCD behaviuor
Texas_Ranger Offline
Member

Registered: 12/17/01
Posts: 2343
Loc: Vienna, Austria
To me this sounds like juice somewhere in the neutral, maybe even ahead of the RCD. I'd try to check for anything of that kind.
Just my 2 cents.

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#133438 - 08/05/02 03:25 AM Re: RCD behaviuor
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Hi Chris, & welcome!

As Texas has said, the neutral on the load side of the RCD could be the problem. Is there any way that it could have been cross-connected with another neutral somewhere?

The other possibility that springs to mind is simply a faulty mechanism in the RCD. You said it works O.K. on the bench, but I'm assuming that on the bench test the device is laying on its back rather than being mounted vertically. I've found faulty units that will only latch when held a certain way.

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#133439 - 08/05/02 05:22 PM Re: RCD behaviuor
ChrisO Offline
Member

Registered: 07/31/02
Posts: 22
Loc: St Ives, Cornwall, UK
Thnx for the welcome


As Texas has said, the neutral on the load side of the RCD could be the problem. Is there any way that it could have been cross-connected with another neutral somewhere?

Neutral out was disconnected, neutral in was connected back to the 3 phase bus

The other possibility that springs to mind is simply a faulty mechanism in the RCD. You said it works O.K. on the bench, but I'm assuming that on the bench test the device is laying on its back rather than being mounted vertically. I've found faulty units that will only latch when held a certain way

Didn't consider that - on the bench it was horizontal.

Our Neutral if full of horrible stuff from motor control and SMPS

I wish I'd (as you have) digi photo'ed our old 3Phase incomer - one of those giant cast iron switches that 'clunk' nicely, rather than feeding a bus system ALL 40 odd tails had been jammed into the top of it and compressed into a homogenous lump by bolting the top back on - insulation cooked and cracked and smelly.

This was fed from an old domestic 3phase that supplied some cottages and just got bigger and bigger fuses till heat cycling and arcing killed it.

Much better now 95mm tails and power factor correction.

I'll add my 2 penneth on grounding when I can as it's very controversial for me and I think you've been discussing it.

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#133440 - 08/06/02 10:57 AM Re: RCD behaviuor
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Hmm...

If the RCD still operates fine on the bench and it isn't a mechanical problem, could it be that on the bench you're running it from a cleaner supply?

If so, then maybe it is all the hash on your power grid that's causing the problem.

Just another possibility: I know it shouldn't make any difference to the RCD, but on the bench are you applying the phases in a different order to when it is installed?

I'm just clutching at straws here and thinking that it might have an effect if there's excessive differential noise between phases or on one particular phase to neutral (i.e. the phase that it used inside the RCD to power the circuitry).

Re grounding/earthing, it would be interesting to get some more comments from this side of the Big Pond with our variety of systems. I have a particular dislike for the TT system!

If you read through some of the other posts, you'll see that grounding in the States also regularly poses certain questions and discussions.


[This message has been edited by pauluk (edited 08-06-2002).]

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