New cooker tripping RCD

M

maffoo

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Firstly, I am not an electrician so please go easy on me and if I have omitted anything please ask.

We've had a new cooker and induction hob installed from Ikea. Here's some information on the setup :-
  • New consumer unit, 100A 30mA RCD feeds 8 MCB's
  • First MCB in line from the RCD is a 40A MCB for the cooker
  • New cable from the above MCB to cooker switch (10mm)
  • New cable from cooker isolator switch to cooker terminals behind cooker (10mm)
  • Induction hob wired in to cooker terminals (2.5mm)
  • 13A fused spur wired in to cooker terminals which feeds the cooker (hard wired cable from cooker)
The RCD is intermittently tripping and it "appears" to be the cooker/hob causing this. Here is some information about the various situations after some troubleshooting :-
  • Cooker and hob work fine, appear to have no issues
  • The RCD has never tripped whilst the cooker or hob have been in use, even at the same time
  • The RCD has never tripped whilst the cooker switch has been turned off
  • The RCD has tripped only once when turning on, but mostly when turning off
  • The RCD trips hours after the cooker/hob has stopped being used, but isolator switch remains turned on
  • On one occasion I couldn't get the isolator switch to turn on without the RCD tripping. After switching off the fused spur to the cooker (leaving only the hob) the power could be turned on. As soon as the fused spur to the cooker was turned on, the RCD tripped again
So after troubleshooting the above, I assumed it was the cooker causing the issue so phoned Ikea and they sent a replacement. However, this is physically damaged so also needs to be returned. In the meantime I have read up on earth leakage and got myself an earth leakage meter as there are a lot of recommendations that maybe the leakage is nearing 30mA throughout the house and it may be the hob/cooker are causing this to go over the threshold.

I've not had time to test everything throughout the house yet but I've measured the hob earth leakage and it's 5mA. Considering the whole house is limited to 30mA, this seems a bit high to me. What is the "normal" leakage for an appliance like this? I will test the cooker shortly too and I suspect that this could be "high" as since the cooker has not been connected at all, the RCD hasn't tripped with only the hob connected.

Any comments appreciated.
 
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maffoo said:
As I said in my original message, I purchased an earth leakage meter as I'm interested in finding out what is happening. If there are issues elsewhere in the house, I want to know.
Click to expand...

An earth leakage metre is a pretty pointless purchase unless you have the knowledge how to use it

Did the fuseboard installer give you any paperwork?
 
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Murdoch said:
An earth leakage metre is a pretty pointless purchase unless you have the knowledge how to use it

Did the fuseboard installer give you any paperwork?
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I do know how to use it. I didn't before I learned about it last week but it's not rocket science.

Yes, I have paperwork. Again, what regulations does it not comply with?

If you believe the RCD tripping issue lies with the consumer unit installation quality then that's fine. Otherwise, I'm being led down the wrong path and still have a potentially faulty hob/cooker. When you guys have tested hobs/cookers/appliances etc. previously, what would expect the earth leakage to be? Is an item considered faulty if it's above a certain mA?
 
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maffoo said:
An electrician fitted it. Any information on why it doesn't comply with the regs?
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As Murdoch says, your whole house should not be on one single 30mA RCD - you loose power to everything in the event of a fault (or, as may be the case here, the cumulative leakage gets above the trip threshold of your RCD).

You really need to get the electrician who fitted it to install something more suitable. RCBOs for each circuit is the best setup - you'd still get 8 usable ways as you have now. At the same time they could perform some tests on the installation (these may have and should have been done before the board change) and the cooker to make sure there aren't any underlying issues that are contributing to this problem.
 
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Inspection and testing needs to be carried out before you start swapping things over.

As you have one RCD protecting the whole installation you may well be getting a cumulative effect combined from other circuits causing the RCD to trip.

Not having enough space is no excuse when there's other options such as RCBOs available.

As for non-compliance of regulations, 314 Division of installation has a couple of relevant lines.
 
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Jim_e_Jib said:
As Murdoch says, your whole house should not be on one single 30mA RCD - you loose power to everything in the event of a fault (or, as may be the case here, the cumulative leakage gets above the trip threshold of your RCD).

You really need to get the electrician who fitted it to install something more suitable. RCBOs for each circuit is the best setup - you'd still get 8 usable ways as you have now. At the same time they could perform some tests on the installation (these may have and should have been done before the board change) and the cooker to make sure there aren't any underlying issues that are contributing to this problem.
Click to expand...

Thanks, that's what I was looking for - an actual suggestion :)

So, get rid of the 100A RCD for 100A main switch and replace the MCB's with RCBO's?
 
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maffoo said:
Thanks, that's what I was looking for - an actual suggestion :)

So, get rid of the 100A RCD for 100A main switch and replace the MCB's with RCBO's?
Click to expand...
that's an ideal solution, albeit expensive. what make is the board?
 
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maffoo said:
Yes, I have paperwork. Again, what regulations does it not comply with?

If you believe the RCD tripping issue lies with the consumer unit installation quality then that's fine. Otherwise, I'm being led down the wrong path and still have a potentially faulty hob/cooker. When you guys have tested hobs/cookers/appliances etc. previously, what would expect the earth leakage to be? Is an item considered faulty if it's above a certain mA?
Click to expand...

Best you review the results and let us know what the IR readings are

There is no way you can say its "fine"

No - impossible to state - unless of course its leaking over 22mA

and may I add with a MFT you can't test the RCD either
 
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maffoo said:
Is it possible/within regs to have 1x RCBO protecting just the cooker circuit and an RCD protecting the other circuits?
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You've already stated that there is a space restriction.

Best you get the spark back who did the install to do some more tests and then advise you on how best to make the installation comply with the regs.

Personally I'm very doubtful a spark was involved ... but you could try and convince me
 
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maffoo said:
Is it possible/within regs to have 1x RCBO protecting just the cooker circuit and an RCD protecting the other circuits?
Click to expand...
Not really Maffoo. No electrician is going to fit it this way for a main consumer unit. Also, it would be pretty irresponsible of any electrician to give you step by step instructions on how to do it properly as (no offence intended) it sounds like you may try and do it yourself and even though you may be able to get it working there is lot more too it than that.
My advice is to get an electrician to change the current configuration of the board to all RCBO's. If you wanted an RCD protecting some circuits and some RCBO's protecting others then it is doubtful your current board has the capability to do that as it will probably only have one neutral bar in it.
 
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happyhippydad said:
Not really Maffoo. No electrician is going to fit it this way for a main consumer unit. Also, it would be pretty irresponsible of any electrician to give you step by step instructions on how to do it properly as (no offence intended) it sounds like you may try and do it yourself and even though you may be able to get it working there is lot more too it than that.
My advice is to get an electrician to change the current configuration of the board to all RCBO's. If you wanted and RCD protecting some circuits and some RCBO's protecting others then it is doubtful your current board has the capability to do that as it will probably only have one neutral bar in it.
Click to expand...

Thank you and all of you for the information, which complied with the "be nice" rules :)

Just to be clear, I have no intention of messing with the consumer unit myself. Never have and never will - which is why I'm still alive at 40 :) Whilst I'm confident with most DIY projects, this is something I will leave to the professionals. This has come about out of my natural curiosity and the need to investigate.

It now seems likely that I've had the cooker replaced for no apparent reason :(
 
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Murdoch said:
So @maffoo ............ a "dislike" - what for ......... pointing out the paperwork and compliance certificates you should have

Rather odd feedback IMHO
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It's a forum for advice and that's what I came for. I've confirmed multiple times that I have the paperwork. If your "I know more than you" attitude makes you believe otherwise then so be it. If I had the paperwork here now I could give you an idea of the content and you might be able to check if it's what I should have or not, but I don't, so you can't.

It all comes down to my original post which had all the information I thought I needed. Everyone else has given me sound, decent and friendly advice.
 
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maffoo said:
It's a forum for advice and that's what I came for. I've confirmed multiple times that I have the paperwork. If your "I know more than you" attitude makes you believe otherwise then so be it. If I had the paperwork here now I could give you an idea of the content and you might be able to check if it's what I should have or not, but I don't, so you can't.

It all comes down to my original post which had all the information I thought I needed. Everyone else has given me sound, decent and friendly advice.
Click to expand...

There is nothing wrong with my advice.

It's just it's not what you want to hear ....

It's quite possible this fault was present before the fuseboard was changed and as you have suggested you have bought a new cooker which may not be required ...
 
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If the problem is aggregate leakage throughout the house reaching the trip threshold, be aware that the threshold can be anywhere between 15 and 30mA for an ordinary RCD. It must trip at 30, must not trip below 15mA, many are in the mid 20s.

There are two main mechanisms that cause earth leakage from cooking equipment. Leakage from heating elements such as those in an oven or grill, is resistive, and often occurs if the element has been in storage for a while until it has had some use. The resistance will show up on an insulation test, and vary widely with element temperature and time since switch on/off. OTOH, leakage from induction hobs is mainly capacitive from interference suppressors. This will not show up as bad insulation on a 500V DC IR test, only as leakage when AC power is applied. So an IR test that showed, for example, that the oven had much lower IR than the hob, wouldn't prove that it was just the oven at fault.

It sounds like your CU is non-compliant. If the problem is aggregate leakage, sorting out the CU will probably cure the tripping. If the problem is actually a faulty appliance, it might not. There seems little point arguing this further until we have some numerical results from the tests.
 
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maffoo

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