Discuss Rcd not tripping when tested ? in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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huntos33

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Been to a job today where the customer is saying thier RCD is randomly tripping, TT system new job all wired 6 months ago ZE 0.70 ( Cracking TT ZE) Earth loops and ins res test all fine, But the RCD wont trip when tested with my tester , Started with a ramp test no trip, auto tested all 6 tests no trip at 1x or 5x rcd . Oddly the other rcd on the other curuicts is fine, replaced rcd with new same issue wont trip but does manual trip with button , now im confused it may be something simple i missing. It's a crabtree star breaker 30/30 set up.

Any Ideas ?
 

Strima

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Tested at the RCD with all loads removed?
 
1

1shortcircuit

I've had this once, two separate RCD's both tested with no loads connected and wouldn't trip. Tested at closest socket and RCD's operated fine.
 

telectrix

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but have you tried testing at the RCD itself with all the relevant MCBs OFF?
 

telectrix

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then i would think that it's either incorrect wiring or you got a couple of dodgy RCDs. try swapping them round tom see if the one that works on the other side trips in place of the one that doesn't. if so, it's deffo the RCD at fault.
 

Strima

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Had the same thing before on an a new BG board, it turned out the neutrals were the wrong way round. But as this board has been in and working for a few months I doubt it's that.

All cable terminations within the board OK?
 

telectrix

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loose connection on RCD tails?????? check the manufacturers connections as well.
 

SPARTYKUS

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Are you sure your connections are correct. When you test at socket & it works, i presume youre using a plug in lead with an MFT,etc. if Im not mistaken the meter needs the earth to make the test work....so...."using inference & deduction my dear Holmes" Im guessing your green lead isnt connected to a reliable earth and therefore it isnt working (the RCD test).


Just a guess, don't quote me
 
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huntos33

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Istalled a new RCd unit from the wholesaler , can't swap the other its different , im thinking the boards been adapted some how, im sure the installs not been done by a spark well not a registed one but all the conections leads etc look right and the earths fine as mentioned at the start.
 

SPARTYKUS

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Tel, yes, but just thinking if main earth is disconn'd somewhere for example, leads might be ok looking at them but ... Dunno.


Is that 0.70 a true Ze of just the earth rod or with parallel paths still connected?
 

Des 56

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Originally Posted by telectrix
but have you tried testing at the RCD itself with all the relevant MCBs OFF?



Yes Done this to


TT Ze of 0.7
Something not adding up there

Are the insulation resistance values ok
Were the outgoing neutrals also disconected for the rcd test?


 
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huntos33

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Originally Posted by telectrix
but have you tried testing at the RCD itself with all the relevant MCBs OFF?






TT Ze of 0.7
Something not adding up there

Are the insulation resistance values ok
Were the outgoing neutrals also disconected for the rcd test?


See im baffled by the ze yes water and gas bond disconected Defo tt even got a note on the cut out dont supply PME ,16mm to 3/8 spike at source then a 16mm 3 core swa via a switch fuse to the DB, i never disconected outgoing neutrals on my rcd test at the unit its self , the testers only 3 months old but im hearing there are issues with the earth pins inside it's a robin MFT going to borrow a mates and see if thats the issue, but i just can't understand one working and the other not. Looking in the board im not 100% its not been adapted from a old 100amp 30/ma split load style and the busbars etc might not be right but it all seemed to be conected fine to me. A longer look maybe required apon my return i think.
 
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MarkieSparkie

See im baffled by the ze yes water and gas bond disconected Defo tt even got a note on the cut out dont supply PME ,16mm to 3/8 spike at source then a 16mm 3 core swa via a switch fuse to the DB, i never disconected outgoing neutrals on my rcd test at the unit its self , the testers only 3 months old but im hearing there are issues with the earth pins inside it's a robin MFT going to borrow a mates and see if thats the issue, but i just can't understand one working and the other not. Looking in the board im not 100% its not been adapted from a old 100amp 30/ma split load style and the busbars etc might not be right but it all seemed to be conected fine to me. A longer look maybe required apon my return i think.
Post some photos of the DB, many heads looking at this may well be better than one. I'm not aware of the Robin MFT (what model? KTS1625?) earth pin issue you mention.
 

telectrix

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the starbreaker RCDs are weird. one takes up 3 ways and one takes up 2 ways. not interchangeable. that's the only thing i hate about these boards.
 
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huntos33

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Post some photos of the DB, many heads looking at this may well be better than one. I'm not aware of the Robin MFT (what model? KTS1625?) earth pin issue you mention.
Thats the one several people have mentioned issues with the earthlead not inseting fully ? or not making proper conection and having to return them.
 
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huntos33

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the starbreaker RCDs are weird. one takes up 3 ways and one takes up 2 ways. not interchangeable. that's the only thing i hate about these boards.
Thats the one the first rcd has 2 pins which span the busbar giving you your l and the Neutrals one in one out ( conected either way acordinf to the instructions, the other has live in from the btm of the MS and the neutral from the common n bar, then n up to the respective n bar, this is all fine guess it must be a wiring issue of some kind , start from the begining work my through
 
E

Engineer54

See im baffled by the ze yes water and gas bond disconected Defo tt even got a note on the cut out dont supply PME ,16mm to 3/8 spike at source then a 16mm 3 core swa via a switch fuse to the DB, i never disconected outgoing neutrals on my rcd test at the unit its self , the testers only 3 months old but im hearing there are issues with the earth pins inside it's a robin MFT going to borrow a mates and see if thats the issue, but i just can't understand one working and the other not. Looking in the board im not 100% its not been adapted from a old 100amp 30/ma split load style and the busbars etc might not be right but it all seemed to be conected fine to me. A longer look maybe required apon my return i think.

An Ra of 0.70 ohms on a 3/8'' twig?? Not even in your wildest dreams!! lol!!!, Even the dammed cable is bigger than the spike it's attached too....
 
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huntos33

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An Ra of 0.70 ohms on a 3/8'' twig?? Not even in your wildest dreams!! lol!!!, Even the dammed cable is bigger than the spike it's attached too....
Telling you now ZE of 0.70 droping to around 0.63 on zs I'm curious as to why its so low but thats what im getting, im back next week with a another tester to double check readings
 
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huntos33

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just a quick update on this ,Been back today changed the bus bar and fitted 4 seprate rccbos got 3 out 4 curcuits passing the rcd and other relevent tests now just 1 ring to go now that trip for love nor money but ever other test is fine !
 
E

Engineer54

just a quick update on this ,Been back today changed the bus bar and fitted 4 seprate rccbos got 3 out 4 curcuits passing the rcd and other relevent tests now just 1 ring to go now that trip for love nor money but ever other test is fine !
And the outstanding Ra values on a 3/8th twig??
 

Rob

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Engineer54

It's hit something lol but thats what it is, used 2 diff testers supplys overhead so it not that
I'd still have trouble believing a 0.63 Ra with a metre long 3/8 twig, even if driven into a salt marsh. Something just isn't right here!!!
 

SPARTYKUS

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My gut feeling is still a parallel path to a TNCS Connected service of another premises, but as you say huntos33 all other paths disconnected when reading Ze. Nice and chewy
 
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