Strange RCD test result

[sparkytim]

Installed a new shower circuit this week in a property I rewired 26 years ago, it still had a spare way on the RCD side of the split load Crabtree starbreaker Consumer Unit and I had a 40 Amp B type MCB (pre plug in busbar type) so duly utilised the spare way as you do.

All hunky dory untill we come to test the RCD, (30m A BS4293).

1x In ok 28.2 m Secs, but when tried 5x it trips BUT keep getting > 40m Sec.

Ramp test ok @ 23 m A and 0.5 x In no trip ok.

So just can't work it out, trips @ 30 m A within 40 m Sec (<200 mSec required) but 150 m A wont' trip within 40 m Sec requirement.

Any ideas?

:C

 

[binky]

Change batteries in test gear ??? Have had something like this, assumed faulty RCD due to not being operated for so long ( no -one pushing test button) and changed it. But it does seem weired to fail the higher test.

 

[Adrian]

have you tried testing at 150ma on the tester instead of x5 @30ma

because I had a similar result with a 100ma rcd my tester would read over on x5 but read ok on 500ma

 

[batty]

Are the tripping times for bs4293 the same as modern trips haven't got books to hand to look.

 

[tom1]

Are the tripping times for bs4293 the same as modern trips haven't got books to hand to look.

think its 200 ms and 40ms for 4293

and 300ms and 40ms for 61008

 

[sparkytim]

Yup thats correct.

Thanks guys, will double check my 1553 and try with it with my older 1552 (no 150m A range on RCD testers but will try 100 m A and see what happens)

 

[septiclecky]

Installed a new shower circuit this week in a property I rewired 26 years ago, it still had a spare way on the RCD side of the split load Crabtree starbreaker Consumer Unit and I had a 40 Amp B type MCB (pre plug in busbar type) so duly utilised the spare way as you do.All hunky dory untill we come to test the RCD, (30m A BS4293).

1x In ok 28.2 m Secs, but when tried 5x it trips BUT keep getting > 40m Sec.

Ramp test ok @ 23 m A and 0.5 x In no trip ok.

So just can't work it out, trips @ 30 m A within 40 m Sec (<200 mSec required) but 150 m A wont' trip within 40 m Sec requirement.

Any ideas?

:C

It means that the RCD has failed as when you are injecting 5 times the tip current it is not tripping within the required time.

replace it.

 

[sparkytim]

Yes thank you for that but......

It does not explain Why it trips out at a LOWER test current injection and within the time scale required.

 

[ianmacd]

Did oyu test the rcd in isolation or with MCB's closed?

 

[sparkytim]

Not sure Ian I was a bit pushed for time, whats your thinking?

 

[ianmacd]

That something on one of the circuits is causing an issue thats stopping it tripping. Could be the meter too, when was it last calibrated? Have you tried it at 5x on another rcd to confirm its ok?