RCD trips when oven reaches temperature or induction hob turned on (intermittent).

[willibob]

Hi all

After tests performed by 3 electricians and no progress, I thought I'd detail my issue on here to see what the consensus is.

Overview
Kitchen refurb completed in December 2019, new Smeg range cooker (fan oven, non-fan oven & 5 induction hob) installed.
Due to Covid, electrician didn't arrive to certify electrics until early 2022.
Tested installation and found a faulty RCD in main consumer unit which he said wasn't tripping as it should when he tested it so it was replaced with a Proteus 63/2/30TA.
Since the RCD was replaced, intermittent tripping of new RCD would occur when turning on any hob (turning it on very slowly would normally avoid the tripping).
More recently, the non-fan oven now trips the RCD every time it reaches temperature and the thermostat kicks in.
The fan oven has not tripped the RCD as yet.

1st Electrician
I contacted the electrician that replaced the RCD and he came back out, tested the wiring from cooker to consumer unit and advised it was an appliance fault which may have been masked by faulty RCD and that I needed an appliance repair person to look at the cooker.

2nd Electrician (from appliance repair company)
Pulled the oven out and disconnected it from the supply. Tested it for earth leaks and gave it a clean bill of health and said that the fault was most likely the wiring to the consumer unit.

3rd Electrician (not an appliance repair person)
Pulled the oven out again. Disconnected the cooker and tested the electrics to consumer unit and found no fault. Tested the now disconnected oven (all controls off) and said there was a 'live to neutral fault' with the appliance.
Reconnected the cooker and put it back in place.

I contacted the appliance repair company and told them what the 3rd electrician said. Was then advised that I'd need a Smeg specialist engineer to test the cooker.

Tried to contact Smeg but they don't even allow you to contact them when a product is out of warranty but instead redirect you to a 'smeg-service' website. I've contacted the only person listed there (based in Glasgow) and he said, as we're based in Helensburgh, he'd pass my details on to a local engineer (I don't hold out a great deal of hope).

So that's where we're up to. No-one can tell me for sure where the fault is, they just tell me where they think it might be.

If I knew for definite that the appliance was faulty then I'd replace it but that's approx £1600 and I'd be a bit gutted if I replaced it and the new one caused the same issue.

Any input would be greatly appreciated.

Cheers

Bill

 

[Fleeting]

This is typical of an element fault that introduces sufficient fault characteristics to trip the rcd when hot.

 

[willibob]

This is typical of an element fault that introduces sufficient fault characteristics to trip the rcd when hot.

Thanks for the rapid response. Much appreciated.

Could a faulty element show as a live to neutral fault when checked across the cooker cable with all controls off?

I appreciate 'a live to neutral fault' is very vague but that's all the electrician could tell me.

 

[Andy™]

elements need to be tested both cold and hot, many only test cold and it passes tests, but will fail when hot...

 

[Geoff1946]

Agree it's dodgy elements, where the mineral insulation has absorbed a little moisture. When the element is cold the moisture is distributed in the insulation material and test OK for electrical insulation. When heated, the moisture is driven towards the cooler ends where it concentrates to give a low resistance which trips RCDs.
Cookers really don't need to be on RCDs, but that now depends on how the feed cable is installed.

 

[willibob]

Agree it's dodgy elements, where the mineral insulation has absorbed a little moisture. When the element is cold the moisture is distributed in the insulation material and test OK for electrical insulation. When heated, the moisture is driven towards the cooler ends where it concentrates to give a low resistance which trips RCDs.
Cookers really don't need to be on RCDs, but that now depends on how the feed cable is installed.

I've seen it mentioned before that cookers don't need to be on an RCD. Can you explain why that's the case? And could a competent electrician redo the wiring so that the cooker is no longer on the RCD?
And just to clarify, the RCD that trips also takes out all of the sockets in the house. Sometimes an individual breaker for a socket circuit also trips but that's rare.
I really appreciate all the responses I've received thus far.

 

[Andy™]

7671 doesnt require cookers to be on an RCD. RCD is only required for the wiring, but often can be wired in such a way that it doesnt need it

as for tripping the sockest too, sounds like a dual split board instead of all RCBO, which is not so well recommended for the obvious reasons of it trips more that just the affected circuit. but they cost less...

 

[Sensai]

When the RCD was replaced and you say the 'wiring' was tested what were the results? Were you given a record of these? RCD trip time, insulation resistance etc? When the 3rd electrician said it was a 'live to neutral' fault did he mean 'line to neutral' or was he talking about the neutral being live? When live is mentioned it does not mean the brown or red cable which is the line cable so this can be confusing and deceptive for customers

 

[BorisJ]

A live to neutral fault would not trip a RCD. Might trip a MCB.

It could, probably not, but could be a faulty RCD.

 

[runningpiglet]

Some RCDs are overly sensitive to spark interference and misinterpret as a current imbalance. Sparks often occur as contacts open like when you say the oven reaches temperature or when turning the switch at an unfortunate speed. The fault is really in two places, firstly the contacts are wearing and need replacement or cleaning or fitting an arc suppression device, secondly the RCD is wrongly detecting arc interference. Fixing the source of problem (the arky contacts) is the better option.

 

[john jeffrey]

Hi all

After tests performed by 3 electricians and no progress, I thought I'd detail my issue on here to see what the consensus is.

Overview
Kitchen refurb completed in December 2019, new Smeg range cooker (fan oven, non-fan oven & 5 induction hob) installed.
Due to Covid, electrician didn't arrive to certify electrics until early 2022.
Tested installation and found a faulty RCD in main consumer unit which he said wasn't tripping as it should when he tested it so it was replaced with a Proteus 63/2/30TA.
Since the RCD was replaced, intermittent tripping of new RCD would occur when turning on any hob (turning it on very slowly would normally avoid the tripping).
More recently, the non-fan oven now trips the RCD every time it reaches temperature and the thermostat kicks in.
The fan oven has not tripped the RCD as yet.

1st Electrician
I contacted the electrician that replaced the RCD and he came back out, tested the wiring from cooker to consumer unit and advised it was an appliance fault which may have been masked by faulty RCD and that I needed an appliance repair person to look at the cooker.

2nd Electrician (from appliance repair company)
Pulled the oven out and disconnected it from the supply. Tested it for earth leaks and gave it a clean bill of health and said that the fault was most likely the wiring to the consumer unit.

3rd Electrician (not an appliance repair person)
Pulled the oven out again. Disconnected the cooker and tested the electrics to consumer unit and found no fault. Tested the now disconnected oven (all controls off) and said there was a 'live to neutral fault' with the appliance.
Reconnected the cooker and put it back in place.

I contacted the appliance repair company and told them what the 3rd electrician said. Was then advised that I'd need a Smeg specialist engineer to test the cooker.

Tried to contact Smeg but they don't even allow you to contact them when a product is out of warranty but instead redirect you to a 'smeg-service' website. I've contacted the only person listed there (based in Glasgow) and he said, as we're based in Helensburgh, he'd pass my details on to a local engineer (I don't hold out a great deal of hope).

So that's where we're up to. No-one can tell me for sure where the fault is, they just tell me where they think it might be.

If I knew for definite that the appliance was faulty then I'd replace it but that's approx £1600 and I'd be a bit gutted if I replaced it and the new one caused the same issue.

Any input would be greatly appreciated.

Cheers

Bill

Need to do a ramp test to check for milliamp leakage from induction hob..these often trip weak rcd's

 

[binky]

As the RCD is shared with other circuits it may be the combination of earth leakage from multiple appliances. I changed my board from shared RCDs to RCBOs due to a similar fault. We have a range cooker with 2 ovens, the smaller oven only gets used at Xmas, and tripped the shared RCD every time, leading to much stress from wife trying to cook Xmas dinner. It never trips the RCBO, restoring peace and harmony to Xmas day..

 

[marcher]

FWIW I found this gem on the Proteus website under technical info.

"Adjacent MCBs, RCBOs or MCB/RCD combinations should
not be continuously loaded at, or approaching, their normal
rated currents when mounted in enclosures. It is also good
engineering practice to make provisions for adequate free air
between devices.
Under these circumstances and, in common with other
manufacturers, we recommend a diversity factor of 66% is
applied to the MCB nominal rated current, especially if the MCB
is expected to be loaded near to or at full rating for more than
one hour.
Thermal issues should also be taken into consideration when
choosing conductor size for the protected circuits."

I wonder if this could affect the RCD trip level after extended operation? Probably not as most RCDs rely on transformer coupling but might explain MCB tripping.

As already mentioned, sharing the RCD with other circuits is also a likely cause.

 

[Jdinduntocher]

I had a similar thing happen with an induction hob guys house had a dual rcd board oven worked fine but as soon as the induction hob turned on it tripped advised him to return it to b&q changed the hob over wired up done the same thing I contacted manufacturers they said they have had issues before. The solution was to fit a 45 amp mcb for the hob. Worked no problem and I checked the hob for earth faults all clear. No further problem message me if you still have faults

 

[Barx]

I have a little spicey version of an 'oven' issue to add. I didn't realise the lady was still having issues until yesterday when she collared me.
Just before xmas her gas oven gave in and as they were hard to come by, she chose to go electric. Asked me to connect up for her. She didn't have a suitable circuit already in place so I installed one (bit of a rush job, trying to get her up and running for xmas dinner).
Anyways, a few days (xmas eve) later she mentioned that the RCD tripped sometimes when she turned the oven off. I could replicate the issue when i nipped round. Leave the oven running, no issue, turn it off.... trip. Re-tested the circuit, all good. I didn't have an RCBO and so put the circuit on non-rcd protected side of board and all seemed fine. Figured a bit of 'built in' leakage was tipping the RCD over the edge. She did mention they had a couple of gremlims previously.

To be honest, I completely forgot about it and so haven't fitted RCBO yet (though as above, circuit doesn't really need it as no socket on isolator and install doesn't dictate RCD protection). She says it still trips the RCD from time to time..... I said, I'm not saying you are telling porkies or anything, but technically it shouldn't be able to (trip the RCD wheh it isn't running through it). Recons if she turns off oven slowly, it usually doesn't trip. Turning knob off fast usually does trip it. Figure that one out.
I now have an RCBO and going to nip round when I get a minute.
I will be testing the actual oven whilst there. Not something I have done yet. You just assume it is ok as it's new (no ***-You-and-Me jokes, thanks )

 

[runningpiglet]

I have a little spicey version of an 'oven' issue to add. I didn't realise the lady was still having issues until yesterday when she collared me.
Just before xmas her gas oven gave in and as they were hard to come by, she chose to go electric. Asked me to connect up for her. She didn't have a suitable circuit already in place so I installed one (bit of a rush job, trying to get her up and running for xmas dinner).
Anyways, a few days (xmas eve) later she mentioned that the RCD tripped sometimes when she turned the oven off. I could replicate the issue when i nipped round. Leave the oven running, no issue, turn it off.... trip. Re-tested the circuit, all good. I didn't have an RCBO and so put the circuit on non-rcd protected side of board and all seemed fine. Figured a bit of 'built in' leakage was tipping the RCD over the edge. She did mention they had a couple of gremlims previously.

To be honest, I completely forgot about it and so haven't fitted RCBO yet (though as above, circuit doesn't really need it as no socket on isolator and install doesn't dictate RCD protection). She says it still trips the RCD from time to time..... I said, I'm not saying you are telling porkies or anything, but technically it shouldn't be able to (trip the RCD wheh it isn't running through it). Recons if she turns off oven slowly, it usually doesn't trip. Turning knob off fast usually does trip it. Figure that one out.
I now have an RCBO and going to nip round when I get a minute.
I will be testing the actual oven whilst there. Not something I have done yet. You just assume it is ok as it's new (no ***-You-and-Me jokes, thanks )

If it were leakage then you’d expect the RCD to trip when turning the oven on. The fact it trips when turning off and can be affected by speed of turning the knob all lends weight to the diagnosis of it being the switch off spark inside the switch being the trigger.