Advice with Electrolux oven

[Luckyboy]

Hello

I don't usually look at appliances but doing a favour for a friend.
He has an Electrolux FQ63XE which is tripping his 30mA RCD after about 5 minutes of switching on - once warm, it'll trip immediately.
He has replaced the temperature limiter which made no difference.
I have brought it to my place to take it apart etc. over the weekend - I currently have it on my bench which is also 30mA RCD protected.
I've turned it on and got it up to 200 degrees without my RCD tripping. (side note, my RCD is good and tested).
I've then powered down, removed cables from both elements.
Continuity for both elements is good, around 0.5 ohms
Insulation resistance (element to earth) for lower element is good >200M ohms
Insulation resistance for upper (dual) element to earth is 0.07 ohms, slowly increasing as it gets cooler.

In my head this points toward an upper element replacement but I want some confirmation from others with more experience on appliances before I tell him to order one.

Any reason my RCD isn't detecting the leakage but his was after a few minutes?

 

[Geoff1946]

I have seen the symptom of tripping RCD on warmup a few times, due I believe to moisture getting into the mineral insulation of an element. My theory is that atmospheric moisture enters the insulation over a period and disperses hardly affecting measurable insulation resistance. On powering up, the increasing heat drives the moisture towards the cooler ends of the element where the greater concentration brings down the resistance until the leakage causes the RCD to trip. A new element should cure the problem, (though I was once told of a brand new element exhibiting such.) Alternatively, if you can keep it hot, perhaps on a non-RCD supply, for long enough you MAY be able to drive the offending moisture out altogether. As I say, just my theory!

 

[Richard-the-Ninth]

It's quite common for electric heating elements in white goods to fail when they get hot. Don't faf with it, get a new one.

 

[SPECIAL LOCATION]

Insulation resistance (element to earth) for lower element is good >200M ohms
Insulation resistance for upper (dual) element to earth is 0.07 ohms, slowly increasing as it gets cooler.

In my head this points toward an upper element replacement but I want some confirmation from others with more experience on appliances before I tell him to order one.

Any reason my RCD isn't detecting the leakage but his was after a few minutes?

My thoughts:-

0.07ohms... is a near dead short to Earth? did you mean 0.07MegOhms..
which is somewhere between 70,000 to 79,999ohms.
(as 1Meg = 1,000,000ohms)

A 70,000ohm earth path will NOT be anywhere near 30ma leakage... Rather well bellow 15ma which must not trip a 30ma RCD..
Which may be why I would guess it is not tripping your RCD?

It would be interesting to know the actual Ramp-Test values for your RCD and your mates RCD..
AND.. is your mates oven circuit on a shared RCD?

If it is shared there could be a cumulative leakage problem with other items also leaking a few ma when combined with the Oven.

ALWAYS remember that historically ovens have had more than their fair share of natural leakage..
and often the manufactures instructions used to state do NOT connect this appliance to a 30ma RCD!

Over the years I have had several random tripping problems with RCD's that also supply ovens...
Which after splitting the oven off onto its own dedicated RCBO have not re-occurred, with no component replacements to the oven.

It is possible that even with a new element you may not cure the RCD issue..

Keep an open mind and assume every aspect of both the appliance and the supply circuit are faulty until you have proved otherwise!
An oversensitive RCD.. supplying a good oven that shares its supply with some other circuits with above average natural leakage can cause all sorts of headaches trying to identify the problem!

 

[Luckyboy]

My thoughts:-

0.07ohms... is a near dead short to Earth? did you mean 0.07MegOhms..
which is somewhere between 70,000 to 79,999ohms.
(as 1Meg = 1,000,000ohms)

A 70,000ohm earth path will NOT be anywhere near 30ma leakage... Rather well bellow 15ma which must not trip a 30ma RCD..
Which may be why I would guess it is not tripping your RCD?

It would be interesting to know the actual Ramp-Test values for your RCD and your mates RCD..
AND.. is your mates oven circuit on a shared RCD?

If it is shared there could be a cumulative leakage problem with other items also leaking a few ma when combined with the Oven.

ALWAYS remember that historically ovens have had more than their fair share of natural leakage..
and often the manufactures instructions used to state do NOT connect this appliance to a 30ma RCD!

Over the years I have had several random tripping problems with RCD's that also supply ovens...
Which after splitting the oven off onto its own dedicated RCBO have not re-occurred, with no component replacements to the oven.

It is possible that even with a new element you may not cure the RCD issue..

Keep an open mind and assume every aspect of both the appliance and the supply circuit are faulty until you have proved otherwise!
An oversensitive RCD.. supplying a good oven that shares its supply with some other circuits with above average natural leakage can cause all sorts of headaches trying to identify the problem!

My sincere apologies! It's been a long day! Yes, 0.07M Ohms...
Ramp test on my RCD is 24ms and is shared between 5 MCBs.

Friends board is also shared RCD across sockets for kitchen, living area and 2 socket circuits. I forgot to do a ramp test on his one - I'll do that next time I'm round.

Don't you think the upper element is showing some deterioration seeing as the lower element is >200MOhms? I've ordered an element already - I'll fit it and hope that it doesn't trip... if it does I'll suggest moving to an RCBO.

Thanks for all of your time and suggestions.

 

[Luckyboy]

FYI I've replaced the upper element which has cured the RCD tripping.

The new element had >500M ohms insulation resistance to earth while the old one had 0.07M ohms!

Thanks again.