Tollerance on RCD trip current

[Ron Lowe]

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

[Mitch]

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]

OK, Thanks for that.

[Dave Osborne]

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]

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

[Peter Scott]

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]

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

[Peter Scott]

Good idea.

Peter Scott