RCD Tripped by Cooker Circuit (Update)

[charlhu]

Many thanks for the numerous thoughtful responses to my initial post. I think the threads have become too long for members to spend time following. So I am starting a new thread here to recap the story deleting redundant info and updating in the light of comments received.
# I will not bore members with an account of my professional qualifications/career etc. Please kindly accept that, although I am not a qualified electrician, I am technically proficient and accustomed to trouble-shooting problems - 95% of which can be solved for oneself by logic and a step-by-step procedure to eliminate possible causes. Regarding DIY - I know what I can comfortably handle myself and where to draw the line and get in a qualified professional. I would NEVER work on an electrical mains board (CU) and, in this instance, my "work" has only been to disconnect an oldcooker from the cable coming from the output side of a cooker switch and then connect a replacement. The "expertise" required for that is the same as fitting a plug - be sure not to interchange line and neutral, ensure the earth is OK and that the connections are tight. In investigating the problem all that I have done is open the cooker switch to check that the original connections are tight and visually inspected the Consumer Unit.
# When I came to live in this bungalow 5 years ago I soon realized that the electrics were sub-standard - no proper earthing system for a start. So I employed a registered electrician to upgrade the installation - new CU with rdc - complete rewiring of the power circuits - new earthing system -etc. The work was done on a cost of materials + daily rate basis so he had no motivation to cut any corners or to skive as I was on site fulltime. On completion and testing he issued an NCEIC certificate - I attach a copy as it just might be useful. Working closely with him for about 5 days I was more than satisfied that he was very competent and trustworthy. (You may wonder why I have not called him back in on this problem but unfortunately he has meanwhile left the area.)
# Fast forward 4 trouble-free years to the present day. I am going to renovate my kitchen. The existing old cooker was not up to much (but no electrical problems) and I decided on a new layout that allows me to incorporate a top-notch multi-function oven and touch-control ceramic hob thatI had bought new and used in France and brought over with me and stored. The old cooker was getting on my wick so I decided, in anticipation of the project, to get rid of it and temporarily locate the oven and hob in the same position (oven below countertop) which also gave the opportunity to check everything was working OK. In the new layout the oven will be mounted in a tower cabinet on another wall to the hob and requires a separate connection. For the interim arrangement I have used the one existing cooker switch/circuit and connected both units to it via a 40A junction box. And here begineth the problem……….

# I have done a number of connections/disconnections/switchoperations/ etc solely as a trouble-shooting exercise - I do NOT, for example, normally use a cooker isolation switch to turn an oven on/off - turns the clock off just for a start.
# Although not chronologically precise, this sequence of events describes what I have found:
· There was no rcd trip problem for the 4 yearsthat the old cooker was connected.
· I now disconnect the old cooker from the cable supplying it ex the cooker switch and connect the cable to a 40A junction box and from there connect the ceramic hob. Still no problem.
· I disconnect the ceramic hob from the junction box and connect the oven in its place. (The oven still has its own cable as wired in by the manufacturer). RCD problem immediately. (Irrelevant whether both units are connected to the jb as it only happens when the oven is connected).
# These are thesymptoms:
· With the cooker switch "on" there is NEVER a trip when switching on the oven or during use.
· Occasionally, when the oven is turned off it trips the rcd so that the two power circuits go down but not the oven itself. (In my last test yesterday I got a trip about once per 10 switch-offs.
· With the oven "off" (better said in"standby mode") the cooker switch frequently trips the rcd irrespective of whether it is being switched "on" or "off". (In my last test yesterday I got a trip about 9 times out of 10). Ex: Both switches are "off" - Turn cooker switch "on" - rcd trips - Reset rcd - Turn oven "on" and carry on cooking without problem.
# As requested, I am attaching some photos of the CU. At the risk of being corrected by the more knowledgeable, it looks 100% to me. Only the two power circuits are on the rcd side and the cooker cable (a bit hard to see at the back in the photos) has its neutral correctly connected to the non-rcd side of the neutral busbar.
# My tuppenceworth is that the problem is not anywhere in the only 4-year old professionally installed CU/rcd/distribution wiring and lies somewhere in what has been recently connected to it. The hob is not guilty. Prime suspects - the oven and its cable. Unlikely to be the oven as it switches on and functions without problem. That leaves the cable and the mystery why an event emanating anywhere in the cooker circuit from its MCB to the oven should trip an rcd to which it is not connected.

 

[Octopus]

Wonder why the installer didn't complete the R1 + R2 or the R2 column on the schedule of tests/inspections? And other boxes on the cert?

 

[Deleted member 9648]

Try carrying out an IR test on all circuits.

 

[Electricalserv]

Wonder why the installer didn't complete the R1 + R2 or the R2 column on the schedule of tests/inspections? And other boxes on the cert?

Very odd

 

[Des 56]

quote
I am attaching some photos of the CU. At therisk of being corrected by the more knowledgeable, it looks 100% to me

I am not normally one for making judgement of others standards,but only posting in order to question your perspective of a 100% effort

That would not be a winner in a "How to fit a consumer unit" contest
I am sorry to say,it would be hard pushed to "qualify" as a contestant

 

[Deleted member 9648]

Wonder why the installer didn't complete the R1 + R2 or the R2 column on the schedule of tests/inspections? And other boxes on the cert?

Wonder where he got 6.0mm with a 4.0mm cpc as well.

 

[Octopus]

If the cooker IS tripping the RCD and its DEFINITELY not on the RCD side of the board I'd looking for a neutral connection from the cooker circuit to one of the rings.

Could be a challange to locate the issue but rewarding when its sorted (and maybe expensive for you)!

 

[charlhu]

Wonder why the installer didn't complete the R1 + R2 or the R2 column on the schedule of tests/inspections? And other boxes on the cert?

Has that any bearing on the problem which has come up now?

 

[charlhu]

Wonder where he got 6.0mm with a 4.0mm cpc as well.

Has that any bearing on the problem which has come up now?

 

[Octopus]

Has that any bearing on the problem which has come up now?

IMHO no, just a sign of somebody cutting corners.

Bet he/she won't be too pleased to see you've posted his details online...... however it may just act as an example of what customers should expect to see on the reports they are given.

 

[Guest123]

I'm sorry I missed the other thread, but from what I gather here the new cooker is tripping the RCD......the cooker circuit is not protected by the RCD though......

 

[charlhu]

quote
I am attaching some photos of the CU. At therisk of being corrected by the more knowledgeable, it looks 100% to me

I am not normally one for making judgement of others standards,but only posting in order to question your perspective of a 100% effort

That would not be a winner in a "How to fit a consumer unit" contest
I am sorry to say,it would be hard pushed to "qualify" as a contestant

Well, as I anticipated, lead with your chin and ...........!
I suppose, at the end of the day, I was satisfied that everything was working and continued to do so until I got into the business of swapping cooking units.

 

[Electricalserv]

If the cooker IS tripping the RCD and its DEFINITELY not on the RCD side of the board I'd looking for a neutral connection from the cooker circuit to one of the rings.

Could be a challange to locate the issue but rewarding when its sorted (and maybe expensive for you)!

With you on this one murdoch lid. If its not on the rcd side and its tripping the RCD theres an interconnection somewhere most likely on one of the rings!

 

[charlhu]

I'm sorry I missed the other thread, but from what I gather here the new cooker is tripping the RCD......the cooker circuit is not protected by the RCD though......

That is correct. And it is elusive since it does not occur when switching the oven on or during use. Two things provoke the rcd trip:
1) Switching the oven off - but only occasionally.
2) Operating the cooker switch to either on or off - almost always.
As the King of Siam said: "Its a puzzlement"

 

[charlhu]

With you on this one murdoch lid. If its not on the rcd side and its tripping the RCD theres an interconnection somewhere most likely on one of the rings!

With this theory keep in mind that demonstrably it NEVER causes a trip with two other items of equipment - the previous cooker and the replacement hob - only with the replacement oven. If there was such an interconnection the rcd does not know or care what is connected on the far end of the cooker circuit and would always trip?

 

[dave462]

your elements have got damp and the only way to dry them out is by disconnecting your rcd and turning on your cooker for a few minutes this dries out your elements,then recon your rcd and it should be ok then

 

[charlhu]

IMHO no, just a sign of somebody cutting corners.

Bet he/she won't be too pleased to see you've posted his details online...... however it may just act as an example of what customers should expect to see on the reports they are given.

Well, it is not a confidential document, my paid-for property and to be used for any relevant purpose e.g. on a sale of the property someone might ask for one and in the case of a rental any responsible letting agent insists on one. Finally, we are all open to "peer review".

 

[Amp David]

Would love to hear what the boys and girls at the NIC would say about his quality form completion though!

 

[charlhu]

your elements have got damp and the only way to dry them out is by disconnecting your rcd and turning on your cooker for a few minutes this dries out your elements,then recon your rcd and it should be ok then

The oven has had many hours of trouble-free use including the 1 1/2 hour 500 degree Celsius pyrolysis cleaning cycle which incinerates all residue to ash and, I do think, would drive out any moisture after reaching 100 degrees C. The problem you have in mind would manifest on switching on and, as made clear, it never does that - only sometimes on switching off.

 

[Des 56]

Its trying to guess an unusual problem from distance when we rely mainly on instrument readings for diagnosing

Unless these instrument readings are known,there can only be suggestions of what may or may not be a problem
It seems the suggestions are exhausted and the only course of action would be to get them

 

[charlhu]

Would love to hear what the boys and girls at the NIC would say about his quality form completion though!

If they gave a damn they would require electricians to submit to them copies of all their certificates. As a pro mechanical engineer well accustomed to designing/constructing/operating potentially lethal equipment and all the codes and paperwork that entails, that suggests to me that these certificates are just a bureaucratic joke. If they were serious there would be controls and follow-up. Next time I may as well do my own!

 

[charlhu]

Its trying to guess an unusual problem from distance when we rely mainly on instrument readings for diagnosing

Unless these instrument readings are known,there can only be suggestions of what may or may not be a problem
It seems the suggestions are exhausted and the only course of action would be to get them

It is some comfort that you call it an unusual problem - I would be chagrined if the bleeding obvious had escaped me. I fully understand and take your point but think that since the problem manifests itself only in one specific situation it renders itself to logical analysis.

 

[Octopus]

The company is still registered with the NICEIC so why don't you call them in?

 

[charlhu]

The company is still registered with the NICEIC so why don't you call them in?

Thoughtful of you to check that out. But after all the caustic comments that you guys have posted?
It is not a "call-back" problem so if I do need to get an electrician in better to start over.

 

[Octopus]

You talk about 4years of successful use of the old cooker then a new layout in the kitchen, new cooker, junction box etc I can't help thinking that the recent changes to the kitchen are the catalyst for your issues.

Time to call in a pro with the test gear to identify me thinks.

 

[charlhu]

You talk about 4years of successful use of the old cooker then a new layout in the kitchen, new cooker, junction box etc I can't help thinking that the recent changes to the kitchen are the catalyst for your issues.

Time to call in a pro with the test gear to identify me thinks.

If you read again - what I have said is that I am PLANNING a new layout and this swap of the cooker is in ANTICIPATION of that. The very small simple job that I have done is the ONLY work that has been done in the kitchen since the rewiring 4 years ago. One small change made - one new problem manifests. It doesn't need Dr. House to conclude that there is a connection between the two and take that as the starting point for a diagnosis.

 

[nikmet]

I think you need to pay some cash and get a proffesional electrician with the correct test gear to come and sort it for you, theres only so much you can do online regards fault finding?
Im sure somebody from here, local to you will sort it for a fair price? (not cheap- but fair!!)

 

[nickblake]

i am going to be critical here , one the guy must be italian , as the board looks like spagheti , the cert is half hartedly filled in , missing noughts incorrect Max Zs values and dashes instead of filling in properly ,as has been mentioned no R1R2 readings in my eyes the insulation readings have just been filled in as you have to do an R1R2 test before an insulation test then the Zs to me its the signe of a rushed job ,i wouldnt accept a cert like that sorry moan over
Lenny has correctly pointed out the cooker is on the non RCD side of the board ,also protected by a 40 amp MCB even worse regarding the oven if its been wired into the 30 amp JB over load risk as i pointed out in original thread chances are the oven wire is 1.5mm flex,, the cable looks old as well , the only way realistically the problem can be sorted out on this would be to get the installation tested again inc a pat test of the oven , untill the installation is proved to be clear then every one could guess what the problem may be , this could be a cross connection some where ,there is a good chance the fault lies some where on the ring circuits and its back feeding but as i have said untill all the circuits are tested properly its difficult to asses

 

[Des 56]

It is some comfort that you call it an unusual problem - I would be chagrined if the bleeding obvious had escaped me. I fully understand and take your point but think that since the problem manifests itself only in one specific situation it renders itself to logical analysis.

Well,I have in times past considered myself to use logic and experience to overcome probably any domestic fault that I have encountered

Using logic is not going to solve your problem,test meters by a person who understands the readings,whoever that may be,is the only logical next step

it also seems to me, that after much effort by others to help distance diagnosis of your problem that your posts are now showing signs of irritation to those who were giving of their time and thoughts

It may be time to admit to yourself that there are some aspects of domestic electrical fault finding that may be a litle out of your scope

 

[nickblake]

I have to agree with Des on this one ,the correct test equipment combined with the experiance of a good spark i feel is the only way to locate the fault here

 

[Octopus]

If you read again - what I have said is that I am PLANNING a new layout and this swap of the cooker is in ANTICIPATION of that. The very small simple job that I have done is the ONLY work that has been done in the kitchen since the rewiring 4 years ago. One small change made - one new problem manifests. It doesn't need Dr. House to conclude that there is a connection between the two and take that as the starting point for a diagnosis.

"Thanks for your help and suggestions" would have been ok but to criticise my imput is somewhat unhelpful and ungrateful. As YOU say, its alsmost certainly something you may have done, so if you turn to outside help, maybe you can save yourself money and the sparky time, if you point out precisely where you made changes.

 

[sparkinlee]

Im sure somebody from here, local to you will sort it for a fair price? (not cheap- but fair!!)

Are forum users allowed to offer within the forum rules?