100ma stype tripping

ohlins · Feb 6, 2012

hello guys been called to a house today, Large old place with 3phase supply.
Phases into 100ma rcd then split to feed duel rcd wylex boards on each floor.The home owners have had trouble with the 100ma s type tripping but not any of the 30ma in the consumer units,i was thinking it may be a fault with a neighbouring property feeding back up the stake (TT system)

Any ideas on way forward,we need the 100 to protect the sub mains.

Cheers all

SPARTYKUS · Feb 6, 2012

Check the sub main !

ohlins · Feb 6, 2012

Thanks for that,first thing we tested.All fine

mechelec · Feb 6, 2012

Ramp test RCD, what current is it tripping at ?

Engineer54 · Feb 7, 2012

If this is a big property with scores of circuits, it could well be an accumulation of leakage current. Don't forget that it's very possible that none of the individual 30mA RCD devices are seeing 30mA, the 100mA will be seeing the overall leakage current. Then of course, there is always the probability of 100Ma S type device being faulty. The only way your going to really confirm or otherwise is to test with a leakage current clamp meter. Ramp testing will at best give you an idea, as they tend to ramp in multiples of test mA, sometimes in multiples of 5mA, depending on what range they are set on. You may well have to increase that front end device to a 300mA S type, ...only by careful testing will let you know that!!