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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Nuisance RCD tripping https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1160630670 Message started by grahamg on Oct 12th, 2006, 6:24am

Title: Nuisance RCD tripping Post by grahamg on Oct 12th, 2006, 6:24am I have a  4 year old Proteus consumer unit, well two of them in fact, one has no RCD and does the lighting etc and the other has a 63A 30mA RCD. The RCD controlled unit is mounted directly above the non RCB unit. We have had nuisance tripping once every week or two since we moved here 3 years ago.  I decided to track it down and bought a one way MCB box and connected one circuit to that, with the aim of trying one circuit there at a time.  The plan was that when a nuisance trip occurs I know it is not the isolated circuit, so connect it back it in the RCD protected unit and move on to the the next circuit.  Once I find the problem circuit I will not have any more nuisance tripping. [assuming it is only one circuit] Then we had an electrical storm with a lightning strike very close and no power through the RCD consumer unit.  I found eventually that although the RCD switch was still in the ON position, no power was going through.  Power was restored by switching the RCD OFF and then ON. Today we lost power again, no storm,  so it seems to be a nuisance trip, once again we had to switch the RCD OFF then ON. So it seems the RCD needs to be replaced. I found a thread here which led me to believe I should get a 30mA RCBO for each of the two circuits with external sockets, and scrap the main RCD altogether.  Also it suggested Proteus is not high quality. Is that correct? Should I avoid Proteus RCBO? Is their unit's rail a standard fit for any manufacturer's MCBO? When bypassing the RCD:- The mains tails go in to the non RCD controlled unit, then there are tails going up to the top of the RCD controlled unit and direct on to the RCD. The neutral then runs from the bottom of the RCD to the neutral junction point. I would prefer not to fit new tails between the units, is there some bridging/connecting device I can buy to replace the RCD and make the wiring simpler?  I suppose I could just buy a 63 Amp 2 pole isolating switch to got there? Many thanks for any advice.

Title: Re: Nuisance RCD tripping Post by sparkyjonny on Oct 12th, 2006, 11:39am Proteus is really poor quality kit - don't waste any more money on it.  Try MEM, Square D, Wylex, Hager or MK (some better than others but all are ok). There's no need for two consumer units by the sound of it - a single split-load unit (where half is RCD protected) would do the job. You don't sound happy doing this - I'd strongly recommend getting a pro in.  He'd also be able to offer his advice asto the best arrangement.

Title: Re: Nuisance RCD tripping Post by grahamg on Oct 12th, 2006, 2:18pm thanks sparkyjonny, especially for the advice on Proteus. I live out in the sticks and the only Pro round here installed this set up! It is a big house, has 18 circuits, 9 on RCD and 9 not. I am  happy to do this job , I did an entire rewire, new consumer unit on another house, which passed the IEEE inspection and test later. Trying to avoid unnecessary work on the tails, but have pretty much decided to fit an insolating switch there. Also I have not used RCBO before. So just checking I am not going in wrong direction, if any one can advise?

Title: Re: Nuisance RCD tripping Post by sparkyjonny on Oct 12th, 2006, 5:02pm Sounds like you could do with a 20 or 24 way board, with RCBOs on the necessary circuits as you suggest.  Even though RCD protection is only NECESSARY for sockets which can feed outdoor equipment, it can be useful to have that level of protection on all socket outlets, especially if you have the luxury of fitting RCBOs (so unlike many setups one fault will not take out half or all of the installation).  Just makes things a bit safer if you have a dodgy/damaged portable appliance and/or kids playing with appliances.

Title: Re: Nuisance RCD tripping Post by The_Trician on Oct 12th, 2006, 9:59pm I have a  4 year old Proteus consumer unit, well two of them in fact, one has no RCD and does the lighting etc and the other has a 63A 30mA RCD. The RCD controlled unit is mounted directly above the non RCB unit. OK, We have had nuisance tripping once every week or two since we moved here 3 years ago.....   No such thing as a 'nuisance trip'! The RCD is just doing it's job - i.e. tripping due to a fault, which is what it is designed to do. I decided to track it down and bought a one way MCB box and connected one circuit to that, with the aim of trying one circuit there at a time.  The plan was that when a nuisance trip occurs I know it is not the isolated circuit, so connect it back it in the RCD protected unit and move on to the the next circuit.  Once I find the problem circuit I will not have any more nuisance tripping. [assuming it is only one circuit] Good idea, but it could take a long time! Might be a better idea to have the whole installation inspected and tested instead? Then we had an electrical storm with a lightning strike very close and no power through the RCD consumer unit.  I found eventually that although the RCD switch was still in the ON position, no power was going through.  Power was restored by switching the RCD OFF and then ON. Not quite sure what you mean by this. Most RCDs can only be reset by switch8ing to 'Off', then to 'On', so this sounds normal to me, and certainly doesn't indicate a faulty RCD. Today we lost power again, no storm,  so it seems to be a nuisance trip, once again we had to switch the RCD OFF then ON. So it seems the RCD needs to be replaced. I'm not sure you are correct in this assumption. I found a thread here which led me to believe I should get a 30mA RCBO for each of the two circuits with external sockets, and scrap the main RCD altogether.  Also it suggested Proteus is not high quality. Is that correct? Should I avoid Proteus RCBO? Is their unit's rail a standard fit for any manufacturer's MCBO? I beleive your Proteus board is working correctly, regardless of quality. Ultimately, it is your money you are spending, but I'd be reluctant to replace a sound board just because of  the brand, and especially because swapping the board won't cure the existing fault! When bypassing the RCD:- The mains tails go in to the non RCD controlled unit, then there are tails going up to the top of the RCD controlled unit and direct on to the RCD. The neutral then runs from the bottom of the RCD to the neutral junction point. I would prefer not to fit new tails between the units, is there some bridging/connecting device I can buy to replace the RCD and make the wiring simpler?  I suppose I could just buy a 63 Amp 2 pole isolating switch to got there? Indeed, you could do just that, but you'd be losing the RCD protection offered by your existing set-up. Rather than chuck a couple of hundred quid on an new CU etc, why not get the existing installation checked out for faults first? BTW - RCBOs are good, but very expensive. You'd be looking at around £30+VAT for each one! Keep us posted as to how you get on - this one sounds interesting. Good luck. TT

Title: Re: Nuisance RCD tripping Post by grahamg on Oct 13th, 2006, 3:20am The_Trician wrote on Oct 12th, 2006, 9:59pm: I have a  4 year old Proteus consumer unit, well two of them in fact, one has no RCD and does the lighting etc and the other has a 63A 30mA RCD. The RCD controlled unit is mounted directly above the non RCB unit. OK, We have had nuisance tripping once every week or two since we moved here 3 years ago.....   No such thing as a 'nuisance trip'! The RCD is just doing it's job - i.e. tripping due to a fault, which is what it is designed to do. I decided to track it down and bought a one way MCB box and connected one circuit to that, with the aim of trying one circuit there at a time.  The plan was that when a nuisance trip occurs I know it is not the isolated circuit, so connect it back it in the RCD protected unit and move on to the the next circuit.  Once I find the problem circuit I will not have any more nuisance tripping. [assuming it is only one circuit] Good idea, but it could take a long time! Might be a better idea to have the whole installation inspected and tested instead? GOOD POINT.  I FORGOT TO SAY, WE HAD AN INSPECTION AND TEST BEFORE WE MOVED IN 2-3 YEARS AGO, I AM OVERSEAS FOR 2 WEEKS NOW BUT WILL FIND THE RESULTS AND POST WHAT SEEEMS RELEVANT.  THE FAULT WAS THERE FROM THE OUTSET OF OUR TIME HERE. Then we had an electrical storm with a lightning strike very close and no power through the RCD consumer unit.  I found eventually that although the RCD switch was still in the ON position, no power was going through.  Power was restored by switching the RCD OFF and then ON. Not quite sure what you mean by this. Most RCDs can only be reset by switching to 'Off', then to 'On', so this sounds normal to me, and certainly doesn't indicate a faulty RCD. WHAT USED TO HAPPEN IS THAT THE SWITCH ON THE RCD MODULE WOULD OCCASIONALLY GO TO THE DOWN - OFF - POSITION AND I INCORRECTLY CALLED THAT A NUISANCE TRIP ABOVE, WE JUST PUSHED IT BACK UP TO - ON -ONCE A WEEK OR SO.  BUT AFTER THE LIGHTNING, THE SWITCH ON THE RCD WAS STILL IN THE UP - ON - POSITION BUT NO POWER WAS GOING THROUGH.  SO WE HAD TO PUSH IT DOWN THEN UP AGAIN TO RESTORE POWER.  THE RCD BEHAVIOUR SEEMS TO HAVE CHANGED - I ASSUMED NOW FAULTY BUT ARE YOU SAYING IT IS OK?  IN WHICH CASE WHAT DOES THE PREVIOUS BEHAVIOUR SUGGEST? Today we lost power again, no storm,  so it seems to be a nuisance trip, once again we had to switch the RCD OFF then ON. So it seems the RCD needs to be replaced. I'm not sure you are correct in this assumption. I found a thread here which led me to believe I should get a 30mA RCBO for each of the two circuits with external sockets, and scrap the main RCD altogether.  Also it suggested Proteus is not high quality. Is that correct? Should I avoid Proteus RCBO? Is their unit's rail a standard fit for any manufacturer's MCBO? I believe your Proteus board is working correctly, regardless of quality. Ultimately, it is your money you are spending, but I'd be reluctant to replace a sound board just because of  the brand, and especially because swapping the board won't cure the existing fault! WELL I CERTAINLY DONT LIKE WASTING MONEY ON NOT CURING THE PROBLEM! When bypassing the RCD:- The mains tails go in to the non RCD controlled unit, then there are tails going up to the top of the RCD controlled unit and direct on to the RCD. The neutral then runs from the bottom of the RCD to the neutral junction point. I would prefer not to fit new tails between the units, is there some bridging/connecting device I can buy to replace the RCD and make the wiring simpler?  I suppose I could just buy a 63 Amp 2 pole isolating switch to got there? Indeed, you could do just that, but you'd be losing the RCD protection offered by your existing set-up. YES I KNEW THAT Rather than chuck a couple of hundred quid on an new CU etc, why not get the existing installation checked out for faults first? WILL POST RESULTS FROM END 2003 - THE TEST WAS CARRIED OUT BY THE PRO WHO INSTALLED IT. BTW - RCBOs are good, but very expensive. You'd be looking at around £30+VAT for each one! YES BUT IT IS WORTH £60 FOR ME TO SOLVE THE TRIPPING ISSUE.  ALSO I HAVE FOUND A READY SOURCE OF NEW MCBO's ON EBAY FOR £15 HOWEVER IF YOU ARE SAYING THERE IS A FAULT SOMEWHERE THEN I PREFER TO FIND THAT AND FIX IT RATHER THAN PATCH AROUND IT. Keep us posted as to how you get on - this one sounds interesting. THANKS FOR YOUR POST TT Good luck. TT

Title: Re: Nuisance RCD tripping Post by grahamg on Oct 13th, 2006, 3:24am wrote on Oct 12th, 2006, 5:02pm: Sounds like you could do with a 20 or 24 way board, with RCBOs on the necessary circuits as you suggest.  Even though RCD protection is only NECESSARY for sockets which can feed outdoor equipment, it can be useful to have that level of protection on all socket outlets, especially if you have the luxury of fitting RCBOs (so unlike many setups one fault will not take out half or all of the installation).  Just makes things a bit safer if you have a dodgy/damaged portable appliance and/or kids playing with appliances. THANKS sparkyjonny  - I am very pleased I posted here and am not going to rush in to anything - I agree it would be better to have an RCD protected unit for all power circuits, even better to have the likely candidates on RCBO as well.

Title: Re: Nuisance RCD tripping Post by sparkyjonny on Oct 13th, 2006, 9:45am No problem. It does sound like you almost definately have a faulty RCD - this may not be the cause of the tripping, but the lightning seems to have damaged it.  I've seen Proteus RCDs behave like this before.

Title: Re: Nuisance RCD tripping Post by The_Trician on Oct 13th, 2006, 7:06pm Concur with S/J if the RCD is now exhibiting the behaviour you describe. With one caveat - you still have some kind of intermittent fault! What brand are the RCBOs you intend to fit? TT

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