S
SPARTYKUS
Always a way La Poste!
Discuss RCD's in series in the Australia area at ElectriciansForums.net
I always put the outside supply on the non RCD side of the board supplied via a RCBO 100ma and 30ma at shed CU this gives full discrimination for the outside circuit.
I've had discrimination with two 30ma RDC's where neither tripped on a fault, so i would not take the chance.
Im really intrested in this, anyone got a technical reason or idea why this could happen?
You would need a time delayed RCD as I understand it from reading posts on the forum?
Could possibly have been a faulty rcd and i by chance took the bad one out of circuit of the two but neither would trip at any x1 or x5, at the time i was doing a job and i did not know there was an upstream one fitted, did job then carried out test and it came to light. Have had this twice before, one was an old farm years ago and another was when someone had an rcd socket on an rcd protected ring, In all cases there was problems with as far as i see it discrimination between the rcd's of the same size. Perhaps it was just my luck or in all cases one rcd was faulty. don't really know and never had a reason to test the one i took out as all worked fine when only one in line. I know about the size/delay difference, same size lottery and assumed this was another thing to add.Faulty RCDs? Cannot see any other reason theres no magic secret with them as far as Im aware. Needasparks what do you mean you had discrim. with two 30mA RCD's?
Ps do you mean a time delayed 30mA device? You can get them
Back to the OP, if the circuit serving the outbuilding is protected by a 30mA RCD, why bother with a 2nd RCD?
Could possibly have been a faulty rcd and i by chance took the bad one out of circuit of the two but neither would trip at any x1 or x5, at the time i was doing a job and i did not know there was an upstream one fitted, did job then carried out test and it came to light. Have had this twice before, one was an old farm years ago and another was when someone had an rcd socket on an rcd protected ring, In all cases there was problems with as far as i see it discrimination between the rcd's of the same size. Perhaps it was just my luck or in all cases one rcd was faulty. don't really know and never had a reason to test the one i took out as all worked fine when only one in line. I know about the size/delay difference, same size lottery and assumed this was another thing to add.
either way i never place two of the same size in series from problems i've experienced in the past. obviously thats just my opinion but in this game we have to stand by what we know and trust, I'm sure we all do and that's what makes the customer call us back to do more work when it does what you say it will.
Ever since I went to my sisters place and did some tests and found her 30 ma rcd welded shut I have always had doubts
about relying solely on 1 rcd, especially in a garden, at least with my sister she had a low enough EFLI to trip an mcb in the event of an earth fault, in a garden
that is TT'd you would not have that luxury, the circuit would simply not switch off in the event of an earth fault and would remain live until someone touched something metal..
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