RCD S type testing

My understanding is the tester gives the RCD a tickle to check it doesn’t trip to early to ensure it should discriminate with a 30 mA RCD downstream stream of it that should trip before the 100 mA time delayed RCD, from memory at less than 70 mA  and less than 130 mS.


Andy Betteridge

Yes, but that happens in an instant and you don't know it's happening as the tester does indicate that it's doing a half current pretest.

What I'm talking about is the actual 30 second countdown shown on the display before it actually does the test.

I don't know if it's only Megger that do this.

Meant to write "the tester doesn't indicate!

I was still thinking about that!


Andy B.

I did an internet search and this was the Top hit




 

Arg seems to have nailed it.


Andy B.

Okay, that makes sense about the timer circuit being given time to reset after the pretest, otherwise it will include the pretest current in the timers start time, but I'm surprised that it needs 30 seconds. I would have thought it would reset within at least 5 seconds.

Mind you, the fact that this is recognised by different manufacturers at 30 seconds shows that this must be an issue.

I wonder why you can bypass this delay by pressing the test button again if you need 30 seconds delay between the pretest and actual test.

I assume that the 30 seconds comes from the type approval standarrd for RCDs - where manufacturers samples are being tested to show they meet the standard - the time between the formal test will be set to be so long that there is no question of the internals having a 'hang-over' from any earlier test.

However, you are quite right,  any real RCD will have either analog integration with capacitors, or some kind of digital counter that resets in a few seconds at most.

So then, you can bypass the 30 second countdown after maybe 5 or 10 seconds and if the result is within limits then fine, but if not then test again with a longer countdown time.