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Topic Title: Rcd why discard
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Created On: 28 April 2014 05:00 PM
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 28 April 2014 05:00 PM
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Dtw21

Posts: 21
Joined: 22 February 2013

I have been asked why if during an RCD test, the RCD or RCBO trips on the 1/2 I test it should be replaced. A side from the higher likelihood of nuisance tripping, what other reasons are there?
 28 April 2014 05:27 PM
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Jaymack

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Originally posted by: Dtw21
I have been asked why if during an RCD test, the RCD or RCBO trips on the 1/2 I test it should be replaced. A side from the higher likelihood of nuisance tripping, what other reasons are there?

Where are you measuring for this to happen? An RCD trip test should be measured by connecting to the unit at the DB. If it is malfunctioning at that point then it requires replacement, assuming that you are testing using the correct parameters, and that your test meter is not on the blink.

Regards
 28 April 2014 06:15 PM
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Dtw21

Posts: 21
Joined: 22 February 2013

I know how to test it. I want to know what, from a safety aspect makes a device tripping on the 1/2 test rot require replacement.
It's a question I have been asked by someone whom knows the answer an has asked if I can't think why.
 28 April 2014 06:30 PM
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dg66

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If the RCD is not operating within its design parameters and trips below its designed tripping threshold, how can you be sure it will operate correctly under real fault conditions?

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Dave(not Cockburn)
 28 April 2014 06:50 PM
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daveparry1

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More likely to cause nuisance tripping I would say is the main reason to replace it.
 28 April 2014 07:32 PM
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mickjeff

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Originally posted by: Dtw21

I know how to test it. I want to know what, from a safety aspect makes a device tripping on the 1/2 test rot require replacement.

It's a question I have been asked by someone whom knows the answer an has asked if I can't think why.


If there is already some minor leakage prior to the test when you test at 15mA (if its a 30mA) it is enough to trip doesn't always mean there is a problem with the RCD.
 28 April 2014 07:38 PM
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daveparry1

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That's the reason why rcd's should be tested at their output terminals with all loads disconnected!
 28 April 2014 09:19 PM
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Dtw21

Posts: 21
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So that's been done and still it trips at 15mA. Can anyone think of any other reasons because I cannot.

Currently I am going with more likely to nuisance trip and outside of design specification.

Maybe that's the only problems it would cause.

I will update tomorrow with the answer I get given.
 28 April 2014 09:42 PM
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daveparry1

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It could also mean that the rcd is a 10m/a device and not a 30m/a one of course!
 30 April 2014 12:19 AM
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mapj1

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Then the half I test should be done at 5mA! there will be situations with noise voltages between E and N where the measured trip current might be measured low on a good device. But the "must not trip before" part of the spec is really about avoiding nuisance tripping, and the 2:1 ratio is to make it easy on the manufacturers, and allow for lightly sprung all mechanical RCDs to be made without too much factory twiddling of setscrews and curling of hairsprings, which the first ones all were, and any change in trip behaviour on those meant the onset of mechanical wear or sticking up of the lubricants. Most modern ones have electronics to do the sensing and level comparison, and then a relatively clunky solenoid, and the range between upper and lower test limits could easily be tighter nowadays, but there is little appetite for over complicating things un-neccesarily.
regards M.

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regards Mike
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