Crabtree starbreaker rcd fault

[nickblake]

i have had the same fault 3 times recently checked every thing and scratched my head new RCD and not been back since

 

[optician]

We have recently come across a similar problem, with no answers yet. We replaced a 100ma rcd, up front on a TT system which was tripping out weekly.
Replaced it with 30ma which started tripping out imediately and irritatingly, ittermittantly and without consistancy. Would not trip at x1 & x5, so like you guys, thought faulty rcd.
Went back later with new rcd and having checked my meter. New rcd, very same problem.
Ok, if there is an earth leakage fault, yes the rcd will trip but surely when you test it it would trip? These are just not tripping under test conditions! can anyone explain? Please.
We put the 100ma back on for now.

 

[Darkwood]

You say your on a tt system are you near to the sub-station by any chance this may cause you issues also believe it or not street lights etc have been known to cause tripping but they are easier to work out due to the lights timings

 

[optician]

Thanks Darkwood, one of my spark colleagues found some info on interference from sub-stations nearby, which suggests that the harmonics cause a dc component in the supply which as we know from the de-loc principle stops the rcd tripping. And causes nuisance tripping! Does any one know more about this possible cause and its remedy?

 

[sparkswillfly]

could be your got more than one appliance giving leakage ie cooker 15ma then then fridge kick in giving another 12 ma causing rcd to let go

 

[optician]

Thanks sparkswillfly, if this were the case would the rcd not test normally? Instead we've had two rcd's that will not trip at x1 or x5 and one even tripped with all mcb's on the off position, no loads and no test equipment.?

 

[sparkswillfly]

try disconnecting one circuit at time sounds like e to n fault in that case

 

[Darkwood]

Do a ramp test with all normal loads running then do a full rcd test with all loads disconnected this will give you the difference which is the leakage present under normal conditions been a tt system clamping the earth on the rod might not give you all the leakage as it may choose other routes as well, also to be noted is neighbouring premises with leakage can in some situations create nuisance tripping too when this starts been the case or similar unresolved reasons then the expensive option of main switch and full board or rcbos instead this gives easier diagnostics if fault is present, and consider several visits will start to cost alot it can sometimes be just as easy to do this for similar cost.