Tollerance on RCD trip current

Ron Lowe

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Mar 4, 2010, 1:53:43 PM3/4/10

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Hi, All.

What is regarded as the acceptable tolerance for an RCD tripping current?

Let's assume a 30mA RCD.

I've read that the tollerance is that it must trip between 50% and 100%
of the rated value. ( ie it may trip at 15mA and still be in spec ). I
didn't trust the source of that quote too much, so I'd like a second
opinion.

Thanks

--
Ron

Mitch

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Mar 4, 2010, 3:02:53 PM3/4/10

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"Ron Lowe" <d...@null.com> wrote in message
news:hmovjp$oha$1...@news.eternal-september.org...

The standard test is 0.5* trip current (at which it must stay closed) and
then at 1* trip current (at which it must trip). Did one yesterday which
went at 24mA (30mA type) which is typical using additional ramp test (i.e.
exactly what current it trips at). So if it tripped at 15mA (0.5I) it would
fail, but 16mA would pass.

Mitch

Ron Lowe

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Mar 4, 2010, 4:53:53 PM3/4/10

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Mitch wrote:
>>
>> What is regarded as the acceptable tolerance for an RCD tripping current?
>> Let's assume a 30mA RCD.
>>
>> I've read that the tollerance is that it must trip between 50% and 100% of
>> the rated value. ( ie it may trip at 15mA and still be in spec ). I
>> didn't trust the source of that quote too much, so I'd like a second
>> opinion.

> The standard test is 0.5* trip current (at which it must stay closed) and

> then at 1* trip current (at which it must trip). Did one yesterday which
> went at 24mA (30mA type) which is typical using additional ramp test (i.e.
> exactly what current it trips at). So if it tripped at 15mA (0.5I) it would
> fail, but 16mA would pass.
>
> Mitch
>
>

OK, Thanks for that.

--
Ron

Dave Osborne

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Mar 4, 2010, 7:53:59 PM3/4/10

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As Mitch said, the standard is that it must *not* trip at 15mA and it
*must* trip at 30mA. It *must* trip at 150mA (5 * 30mA) within 40ms.

In practice, if it trips close to 15mA then it will often be a nuisance,
so manufacturers do tend to go for higher trip currents.

However, the circuitry in an RCD is cruder than you might think, so any
given RCD could be anywhere between (say) 17mA and 27mA trip threshold.

Having said that, IME Hager RCDs consistently trip at or about
27mA-28mA, so are a good choice if you are replacing an RCD which is a
little over sensitive.

cynic

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Mar 5, 2010, 6:05:49 AM3/5/10

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FWIW every Hager 30mA RCD I have ramp tested seems to trip at 27mA

Peter Scott

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Mar 5, 2010, 11:48:32 AM3/5/10

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Very useful information. I have a Crabtree 30 mA trip which I am sure is
at the bottom end of the tolerance. Trips quite often when things like
PCs and laptop PSUs are switched on. Pain in the neck. I'll fit a Hager
when the time comes.

Peter Scott

cynic

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Mar 5, 2010, 2:26:24 PM3/5/10

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> Peter Scott- Hide quoted text -
>
> - Show quoted text -

I'd suggest ramp testing your existing RCD - it may be tripping at a
similar level to the Hager (or not)

Peter Scott

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Mar 6, 2010, 8:21:03 AM3/6/10

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Good idea.

Peter Scott