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Topic Title: Testing portable RCDs
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Created On: 18 June 2011 02:42 pm
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 18 June 2011 02:42 pm
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insafehands

Posts: 57
Joined: 21 January 2009

Hi,

When carrying out testing to verify trip times on a plug-in RCD adaptor or RCD protected extension lead I have encountered the following problem.

Pluging the RCD into a mains socket then the tester into the RCD and starting the test sequence trips the the Consumer Unit RCD protection for the circuit as well as the plug-in RCD adaptor. Althougth this is not a huge problem it is very inconvieniant as any appliances connected to the RCD protected circuit loose power.

I would have thought that the plug-in RCD adaptor would trip first before the Consumer Unit RCD!

What is the best procedure to follow?

Regards

Kev
 18 June 2011 02:52 pm
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Phoenix151

Posts: 103
Joined: 14 February 2007

As they are both (likely) 30mA devices then they are both likely to trip together, or whichever one happens to be marginly faster will go first.

In order to test rcds in series like this, you should put your earth probe from your rcd tester on the *neutral* before the rcd under test, rather than the earth... so that an inbalence is created only in the RCD you want to test.

The practical application of this to an rcd ext lead may involve a BS1363 breakout plug or two...
 19 June 2011 12:25 am
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deleted_1_Grizzly01

Posts: 250
Joined: 21 February 2008

or just get one of these:

Seaward NTB-1
 19 June 2011 12:29 am
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sparkingchip

Posts: 11682
Joined: 18 January 2003

So is that a fancy job with a transformer in it, or just a box with a earth/ neutral link in it?

Andy
 19 June 2011 07:30 am
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ebee

Posts: 6735
Joined: 02 December 2004

"or just a box with a earth/ neutral link in it? "

Hardly, would trip yer circuit RCD, wouldn't it?

Actually it depends on what you mean by that.
If you mean that incoming L = outgoing L and Incoming N = outgoing N and the outgoing N linked also to outgoing E then, I think, that should work as an RCD tester socket but would be dangerous if ever used to plug an appliance into.

My guess is (the name helps) that it's an isolating transformer and at the output one pole is used as L and the other pole as both N & E and a warning not to be used for appliances

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 20 June 2011 12:56 pm
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AJJewsbury

Posts: 17795
Joined: 13 August 2003

If you mean that incoming L = outgoing L and Incoming N = outgoing N and the outgoing N linked also to outgoing E then

My box of test kit has a plug & socket wired up exactly like that - with a suitably large warning label on it. I made it up so I could run 25A loop test on a known socket for periodic checking of my loop tester without tripping the circuit's RCD - but it works just as well to "isolate" RCDs.

- Andy.
 20 June 2011 03:16 pm
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ebee

Posts: 6735
Joined: 02 December 2004

Does not even trip the 10mA RCD before it.
Not that I'm admitting that I made such a thing without an isolating transformer in a lock up cupboard purely for comparing loop testers of course

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
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