Crabtree starbreaker rcd fault

[monkeyelectric]

Hi guys, just been to a job where the rcd trips out as and when it wants, when the guy goes to switch it back on it won't hold even with all the mcb's switched off, he says sometimes it can be a few minutes before it can be switched back on and sometimes can be up to an hour which must be really annoying for him, i did and rcd test and could not make the rcd trip at all, even on the ramp test it would'nt trip Has anyone had this problem before? is it just likely to be a faulty rcd? cheers

 

[wetny]

is there a neutral earh fault?

 

[telectrix]

if the rcd won't trip when you test it, it is U/S irrespective of whether it nuisance trips or not. change it. CYA

 

[vitoboy]

yep
and check the main earth..could be variable
check the main neutral...the same
check the battery in your tester as this can lead to allsorts of random test results for rcds..

 

[nickblake]

Yep definatly a faulty RCD , i have found alot of RCD that trip without reason middle of the night etc and the slightest operation will trip them i have just changed one for the exact reason random tripping when i switched off the main switch to replace it the RCD tripped , so would recommend replacing it , and as you have said you have tested it and it didnt trip so its faulty

 

[monkeyelectric]

is there a neutral earh fault?

Yes bud, i had more time to investigate and there was a neutral earth fault on the cooker and on the ring was an ir reading of 1.5 megohms so may be causing it to trip.

I tested the rcd again on saturday and it tripped fine, i was tired when looking the other night so must have just been a spaz about it, and i could'nt find the neutral earth fault on the ring in the 2 hours i had, it is one huge ring though, the whole 3 storey house is on it, must be around 40 sockets, not the way i would do things but it was wired 10 years ago but someone who belonged in the zoo according to the house owner, i got to go back tomorrow to see how things are.Those starbreaker rcd's are £50-£60 each, hell of a price

 

[Darkwood]

Irrispective of previous advice on this post, all you need to do is do a full rcd test as though you were doing a T & I, do a trip test on the front of the rcd and then do a ramp test to see at what mA the rcd trips which should be between 20 and 30 mA, if it trips at less than this their may be existing earth leakage on the circuit which can be proved by disconnecting the circuit and ramp testing the rcd direct, if this proves ok then the problem lies within the circuit or an item plugged in or connected. Earth leakage can arise from many loads, are their alot of electronic equipment on the circuit like computers etc as each one can leak up to 3mA in noise.

 

[Deleted member 9648]

I would ignore an IR reading of 1.5Mohms as a cause of tripping.....bear in mind that up until very recently the minimum was 1.0 Mohm....and going back even further 0,5Mohm.....1,5Mohms on an existing circuit isnt worth wasting your time on......In practice only IR readings less than 0.5 Mohm are likely to be the cause of nuisance tripping.

 

[monkeyelectric]

Irrispective of previous advice on this post, all you need to do is do a full rcd test as though you were doing a T & I, do a trip test on the front of the rcd and then do a ramp test to see at what mA the rcd trips which should be between 20 and 30 mA, if it trips at less than this their may be existing earth leakage on the circuit which can be proved by disconnecting the circuit and ramp testing the rcd direct, if this proves ok then the problem lies within the circuit or an item plugged in or connected. Earth leakage can arise from many loads, are their alot of electronic equipment on the circuit like computers etc as each one can leak up to 3mA in noise.

Yeah i done that bud it tripped at 21mA, i think that the cooker is the most likely candidate for the tripping but all will be revealed when i go back today, there are a few computers and electronic equipment on the ring its absolutely daft that there is only 1 ring for the whole house so there is another possible cause

 

[monkeyelectric]

I would ignore an IR reading of 1.5Mohms as a cause of tripping.....bear in mind that up until very recently the minimum was 1.0 Mohm....and going back even further 0,5Mohm.....1,5Mohms on an existing circuit isnt worth wasting your time on......In practice only IR readings less than 0.5 Mohm are likely to be the cause of nuisance tripping.

I suppose you're right it is a bit high to be concerned about but i was just looking for possible causes and narrowed it down to the cooker and ring main, cooker eliminated so i'll go back this morning and see what has happened

 

[Darkwood]

Well good luck, as the intermittent cause can sometimes be a bitch to locate especially if a trapped wire say under a floorboard that only shows as you walk over it, if only a couple of computers on then i wouldnt worry about it, see if you can gather more info like if it trips when they are all out etc , or middle of the night or even what the weather is like,,,,, if you find they are always awake and in the house then you need them to list what they were doing and what was plugged in, it can be a long winded task but you need to explain this to them and let them do all the recording of events .....
if possible and you have a good 2nd hand rcd unit then by pass the original and fit it (in enclosure if necessary) as this will tell you if rcd unit is faulty as they can fault intermittently too, so they may seem fine when testing etc but nuisance trip from time to time..

 

[nickblake]

im sure its the RCD thats faulty random tripping points to that , if it was an IR problem it would trip all the time and wouldnt stay on ,as wire puller has said less than 0.5 mohm then may bee

 

[monkeyelectric]

Well good luck, as the intermittent cause can sometimes be a bitch to locate especially if a trapped wire say under a floorboard that only shows as you walk over it, if only a couple of computers on then i wouldnt worry about it, see if you can gather more info like if it trips when they are all out etc , or middle of the night or even what the weather is like,,,,, if you find they are always awake and in the house then you need them to list what they were doing and what was plugged in, it can be a long winded task but you need to explain this to them and let them do all the recording of events .....
if possible and you have a good 2nd hand rcd unit then by pass the original and fit it (in enclosure if necessary) as this will tell you if rcd unit is faulty as they can fault intermittently too, so they may seem fine when testing etc but nuisance trip from time to time..

Cheers Darkwood, it is a pig to find when it intermittent, i once had a similar thing at another house and everything tested fine but narrowed it down while i was there they walked upstairs to go to the toilet and it tripped so i reset and it tripped again when they came back down the stairs, turned out a wire had been put through with the heating pipe which had warn through the insualtion but only created a dead short when the floorboard above was stood on. Unfortunately this one trips when they're all out and when they were away for the weekend or the middle of the night or at anytime it wants apparantly

 

[monkeyelectric]

im sure its the RCD thats faulty random tripping points to that , if it was an IR problem it would trip all the time and wouldnt stay on ,as wire puller has said less than 0.5 mohm then may bee

Cheers Nick, will try what Darkwood said and put a standalone unit in a seperate enclosure just to try it before i go to the expense of buying a starbreaker

 

[nickblake]

without a doubt an 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