Purpose of testing RCD at 1x and 5x

[StopTapBob]

Can some one please explain why we test at 1 x and then 5 x the rated capatity for a 30Ma RCD? I understand the purpose of the test but I cannot remeber the reason why its 1 and 5 times. Thanks.

 

[Deleted member 26818]

1 X to see whether it trips at the rated current, 5 x to see if it trips in the required time.
1/2 x to see if the device is too sensitive.

 

[StopTapBob]

Yes but why 5 times ?? (150ma) why not 6 or 7 ??

 

[bugsy]

Yes but why 5 times ?? (150ma) why not 6 or 7 ??

used to six until we went decimal

 

[yellowvanman]

Because thats what it says in BS7671 - 415.1.1

 

[Deleted member 26818]

Because BS7671 requires that 30mA RCDs shall operate within 40ms at 150mA.

 

[StopTapBob]

I know what the regs states but does anyone know why we test at these ?
It was explained to me at college but I cannot remember it all. I know we test at 30 ma because humans can take up to 30 ma without causing death. Between 60 and 100 ma can prove to be fatal. But why 5x ???

 

[Smugley]

I don't know, so this is a guess: we are checking that the RCD is performing as it is expected to according to whichever British Standard it was manufactured to. I haven't seen a copy of BS61008 for example, but I expect there is a time/current curve which specifies the minimum requirements and to ensure compliance more than one test current must be used.

 

[StopTapBob]

It's not to do with that I don't think. I am sure its to do with the effect of shock on the body but I can't remember exactly what the tutor said.

 

[Engineer54]

It's not to do with that I don't think. I am sure its to do with the effect of shock on the body but I can't remember exactly what the tutor said.

Correct, ...It's all to do with levels of fault current that present itself at the RCD, and the times taken for the RCD device to operate at those higher fault levels...

 

[StopTapBob]

Can u expand a bit more on that. Why specifically 5 times. Why not ten times. ??

 

[Engineer54]

No idea, ...but probably a lot to do with the harmonization with European standards. We state.... 1/2x, 1x, 5x for 30mA RCDs, and the EN state.... 15mA, 30mA, 150mA for 30mA RCDs, ... in there testing regulations.

150mA is when you think about it, a pretty decent test for a 30mA RCD device. There is probably going to be a limit to the speed of tripping an RCD and 0.4 sec is all that is required for other protection devices....