Oven Element faulty.....or is it?

[catdog]

Hi guys.

Oven Element was knackered-open circuit. Just fitted new one last night-started to heat up the tripped rcd.....

Did IR to find between LN to earth was 0.45Mohms. Managed to get it back on again and thought might be able to blast out any moisture. It strangely heated up and the did an insulation resistance and it was then showing 0.2M ohms.

Took it out and this morn just did another IR and it is sitting at 45Mohms!

Was planning to return it but if they test it and it's 45Mohms.....

Any thoughts?!

 

[telectrix]

damp

 

[Wilko]

Hi - the new element may have been in storage for a while (maybe a couple of years?) and absorbed the damp. It should be ok now .

 

[Lucien Nunes]

This is normal for sheathed heating elements. As they heat, moisture inside is driven towards the cooler ends where it condenses. The concentrated zone of moisture lowers the IR, until it too reaches a high enough temp for the moisture to evaporate and the IR goes back up. The cycle can repeat at each warm-up until the excess moisture from storage has dissipated.

 

[marconi]

Is a solution to place the new element in one's home oven at say 110C for an hour (or more?) before fitting it? And to take some IR measurements once it has cooled down.

 

[Lucien Nunes]

That should work, but it might take longer than running the element at its full working temp as the vapour pressure of the water will be lower. I've baked them on an isolating transformer in the past.

 

[catdog]

Thanks guys.

Yeah I did try to 'bake' it in the secondary top oven at the customers house but as wasn't fan oven was taking too long-will try in my own oven today-seems a hassle to send it back and wait for replacement!

 

[Deleted member 105018]

I do a few jobs installing industrial heating elements. Big stuff. Manufacturer (watlow) always state that they must be soaked (ie baked) before being used. They use a powder to surround the elements in the actual rod. Seemingly the powder acts as a desiccant and actually soaks up moisture if they’re stored. Not sure oven elements are the same mind.

 

[Deleted member 26818]

The powder is Magnesium Oxide and is hygroscopic.
Yes it’s the same in domestic cooker elements as in industrial heating elements.
You can get ceramic elements where the heating wire is screen printed to the ceramic.
Don’t take kindly to oven cleaners and scrubbing brushes though.

 

[123]

And this thread is from July, I'd like to think its been sorted by now and they aren't eating takeaways waiting on a response.

 

[Deleted member 105018]

And I’m not looking st the dates. Doh.

 

[pirate]

Damp...almost certainly what you all said. have had constant problems with ovens in holiday home where the damp atmosphere from unoccupied house causes failures...the local guys say it happens all the time.
Average lifespan for a TV in that scenario is 2 years.

 

[catdog]

Sorry thought I'd replied to this! So yeah took element home and baked it in my own oven and it did the trick!

Randomly the next day I went to another faulty oven job except this time was in new build house that had never been lived in and was unoccupied for 1 year with brand new oven. Thankfully was the grill element that was down on insulation resistance. So I disconnected grill element and turned the oven on (was a single oven) for about 30 mins (however long it took to drink my coffee ) and it did the trick!

I wonder how many elements have been replaced due to an incorrect interpretation of an IR test....

 

[Deleted member 26818]

Now if the ovens were not on an RCD, you probably wouldn’t notice this at all.

 

[catdog]

Indeed. I did wonder about rigging the element up to a socket that wasn't on an rcd which would have been faster than baking it!