Hager Split CU, RCD now nuisance tripping.

[Matt Smith]

Hi all,
I fitted a new Hager CU about a year and a half ago for a neighbour in our area, and all was fine, although the people who live in the flat are very odd and not very bright to be generous ! anyways the board has the split 30mA Rcd's one each side and type B MCB's after them.

I have split ring final cct's across the two halves of the board and lights etc..
Problem I have now is that the Rcd covering 3 x MCB's on one side of board keeps dropping out, it covers water heater cylinder, kitchen ring main and another ring main only, all with their own mcb's too. I reset the rcd upon visiting and it tripped again so I tried each mcb load one by one and water heater fine etc.. and offending item was the kitchen ring tripping the rcd after approx 4-5 seconds !

I checked with person that it's been fine for best part of 18 months and they said yes no problems before now, I am therefore unsure if it's tripping on earth leakage or possibly overloading without taking out the mcb ?

They informed me only thing changed was a washing machine a few months back which I am sure they leak to earth and as would the fridge/freezer which is also on kitchen ring.

On inspection in kitchen I found one old single socket feeding a 4 way extension and onto another 4 way lead into which we have a washing machine, fridge/freezer, toaster, steamer for food cooking, and a kettle too and now and then the microwave ! all from one single socket !!

I tried to explain that this is way too much load for a single socket but she told me it's been no problem for 36 years so far..

she asked me to take away the rcd and put in a main switch on the problem side of the split CU which I explained would be illegal and not to 17th regs then.

Today she came back saying she had bought a new 4 way and yet it still trips out !! I don't think they are getting this...

I can't run new rings to split it up as flat is totally concrete and bursting with grot and junk high up every wall and to be fair I do not want to work any further in the premises as it's a health hazard.

Anybody shed any light on how I can counter the nuisance tripping or advice if you think is washer, fridge compressor etc... all just accumulating earth curent or does 4-5 sec delay to trip sound like overloading ? Thanks all, M.

 

[imago]

If we set aside Part 'P' and testing with an MFT for a minute, you still can, and should be able to carry out tests. People were testinmg installations long before the dual 'cure-alls' of Part 'P' and MFTs came along.

So, you shouldn't assume or guess that earth leakage from the new appliance is responsible. It may well be a red herring, and possibly cost you a great deal of time looking for a fault which doesn't exist.

Back to basics, disconnect everything on that circuit. Does the RCD still trip? If it does, investigate the wiring. If not, reconnect the appliances/equipment one at a time and operate them. Does it trip out? If yes then you've narrowed the fault down. If no then get them all operating together one at a time until it does.

95% of electrical faults can be found using very basic principles and a systematic approach. An MFT will speed up the process, but basic test kit will quite often get you there. The issue being that everyone wants to sort out a fault in an instant and rushes the job. There also seems to be a worrying lack of understanding when it comes to basic principles generally as the younger/newer qualified sparks seem to be taught stuff parrot fashion when it comes to calculations and testing, rather than building up to that from the basics.

 

[Heisenberg]

There also seems to be a worrying lack of understanding when it comes to basic principles generally as the younger/newer qualified sparks seem to be taught stuff parrot fashion when it comes to calculations and testing, rather than building up to that from the basics.

Like the OP's misguided belief that the RCD in question provides overload protection.
Everyone's got to start somewhere but to think that someone could possibly be about to sit the 2391 written, and not understand something as fundamental as that, probably illustrates your point perfectly.

That aside, I've very little sympathy for people who undertake board changes without having done any form of testing, and then come a cropper. Also, the fact that the guy is doing installs but does not seem to own any testing kit, is hardly something that should be encouraged.

Cheers

 

[imago]

A few months back I showed a fully qualified spark how to find a L - E short in a lighting circuit. He seemed amazed and was very enthusiastic about learning a 'new way'. The house was being refurbed (replastered, wiring changes, loft insulation, new kitchen, bathroom etc) and second fix going in.

This mysterious technique which caused so much excitement and interest was nothing more than following the upstairs lighting circuit and looking for a reducing resistance, then increasing using a multi-meter. It took twenty minutes to narrow it down to the area above the landing, then find the screw through the cable in the loft.

It wasn't that he was tick, or bad at his job, he was simply too reliant on his MFT and his training was too focussed on formulas, RCDs, and the like IMHO.

 

[Colin Jenkins]

Hello Matt.

Ths is fault-finding now rather than "Inspection", so don't get too hung up on documentation The RCD is operating intermittently; these devices are very reliable so it's 99.99% certain it's seeing leakage of current to earth and doing its job correctly.

If the building has solid walls and flush electrical accessories, with all the rain we've had in the last 12 months the ingress of moisture is a possibility. It does not even have to be visibly damp inide the accessory, just humid - that will be enough to cause the 30 mA RCD to operate.

Perhaps the easiest way to spot which circuit is in trouble is to use an earth leakage clamp meter. With the circuit in normal operation, the clamp meter is closed around Live and Neutral and the imbalance is displayed directly in milliamps. All circuits have little bit of leakage, but if you find one reading 15 milliamps or more, then that is likely to be the source of the trouble. Read each circuit individually and write them all down - it's surprising how the milliamps tot up on some installations.

The Fluke 360 and the Megger DCM300E are both earth leakage clamp meters that would be suitable for this. They cost about £300 each, but are incredibly useful test instruments that will get plenty of use on other jobs. They sometimes appear on E-Bay, or you may be able to hire one locally to sort this earth leakage tripping out.

This is live working, so take care.

I hope this helps.

Regards,

Colin Jenkins

 

[BlueToBits]

Thank you... going to have to try find out what is causing the leakage now, sorry for wasting your time guys.

You are not wasting anybody's time, We've all got time to 'waste' anyhow, if we didn't we wouldn't be here. There will always be those that will shoot you down, It's often difficult to express the something you would say out loud with the same meaning in typed words. That's the nature of forums. Remember that comments are merely opinions, they may or not be factually correct, and I include my own in that.

Having said that, in my opinion, irrespective of what exams or courses we have or have not taken, if we are undertaking installation work, we should always test it. We should understand exactly what we are testing, why we are testing it, and the significance of the test results. Until we are sufficiently conversant with this our electrical work may be at risk of harming someone, not least ourselves. Whether or not any of us decide if we can sleep soundly ignoring this is ultimately up to ourselves and our knowledge and assessment of the risks pertaining to job in hand. Again, it's only my opinion, but the really 'dangerous' electricians are those that work without realising this.

The regulations require that a minimum series of tests are carried out for any particular job, fault finding usually requires much more than this minimum.

 

[Midwest]

Hmmmmm, much better :wink5:

 

[Matt Smith]

O.k. so I have messed up by not testing, I have learned the hard way and just tonight bought a whole 17th edition test kit to replace the Megger 1553 I sold before due to redundancy and two toddlers in the house. I appreciate the slaggings from people like Lurch and others... and I also really Thank Colin, Blue to bits, imago and many others for their experience and teaching me something new going forwards. I am competent and have completed many tests before but on this occasion I failed myself and a customer. I will also like to after all remove my access to the forum and if anybody can tell me how I do this, I would very much appreciate it. Thanks again to the few who do not just want to put people making mistakes down, anyways the person who never made a mistake never learnt anything, I heard...

 

[imago]

OK, you fuc, er, messed up. People have done worse. No reason to leave the forum, there are some very experienced sparks on here and if you stick around you'll learn loads as we all have from them.

Keep it in perspective, take it on the chin and move on

 

[Midwest]

I rest my case. If you'thesaurus' forum, one hit is opportunity. Lets not forget that.

 

[Octopus]

O.k. so I have messed up by not testing, I have learned the hard way and just tonight bought a whole 17th edition test kit to replace the Megger 1553 I sold before due to redundancy and two toddlers in the house. I appreciate the slaggings from people like Lurch and others... and I also really Thank Colin, Blue to bits, imago and many others for their experience and teaching me something new going forwards. I am competent and have completed many tests before but on this occasion I failed myself and a customer. I will also like to after all remove my access to the forum and if anybody can tell me how I do this, I would very much appreciate it. Thanks again to the few who do not just want to put people making mistakes down, anyways the person who never made a mistake never learnt anything, I heard...

Matey, one of my first posts was so badly laid out I got absolutely slated, and deservedly so...... but it taught me a lesson and look at my count now!

 

[Engineer54]

The RCD is operating intermittently; these devices are very reliable

You wouldn't be saying that if you had seen the sheer numbers of RCD devices of all kinds being returned to the manufacture for replacement on my last and previous projects!! That's the problem, many think they are very reliable, when in fact they are nowhere near as reliable as many make them out to be. That goes for all types of RCD and all manufacturers even the top end ones. You only have to just look at the amount of posts on the forum threads, where RCD failures have been highlighted!! lol!! ​

 

[itselectric]

You wouldn't be saying that if you had seen the sheer numbers of RCD devices of all kinds being returned to the manufacture for replacement on my last and previous projects!! That's the problem, many think they are very reliable, when in fact they are nowhere near as reliable as many make them out to be. That goes for all types of RCD and all manufacturers even the top end ones. You only have to just look at the amount of posts on the forum threads, where RCD failures have been highlighted!! lol!! ​

One good reason to get the customer to test the rcd with the button on a regular basis, and for periodical tests although On domestic premises there is a long gap between these.

 

[pencilpusher]

O.k. so I have messed up by not testing, I have learned the hard way and just tonight bought a whole 17th edition test kit to replace the Megger 1553 I sold before due to redundancy and two toddlers in the house. I appreciate the slaggings from people like Lurch and others... and I also really Thank Colin, Blue to bits, imago and many others for their experience and teaching me something new going forwards. I am competent and have completed many tests before but on this occasion I failed myself and a customer. I will also like to after all remove my access to the forum and if anybody can tell me how I do this, I would very much appreciate it. Thanks again to the few who do not just want to put people making mistakes down, anyways the person who never made a mistake never learnt anything, I heard...

Matt, you seem like a decent bloke and you are learning. We all started somewhere and we all make errors. You will learn loads on here but at times will get slated if what you have done goes against good practice, the Regs or your questions don't contain full details. I tell you one thing, you wont change a board again without flashing back to this post. Hang around, have a sense of humour and learn. That's what we all do. (Well most of us anyway!) There are some very experienced people on here who will help you if you set your stall out correctly.