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Dave Osborne[_2_] Dave Osborne[_2_] is offline
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Default Tollerance on RCD trip current

On 04/03/2010 18:53, Ron Lowe wrote:
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


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.