Replaced fan oven element, now trips RCD

[Johnking]

My fan oven element died a few days ago, tripping the mains RCD. Having replaced it a few years ago, I knew what to order and how to do it, so I installed a new one. Everything seemed to go smoothly, but one of the spade terminals on the old element was blackened and worn away, it looked like what happens when a terminal is sparking. The spade connector on the wire was loose on the new element so I cleaned it and pinched it tight. It now fits tightly and the element installed normally. However, within 30s of turning the oven on to test, the mains tripped again. This seems to be to do with the element starting to get hot - I waited half an hour and the same thing happened - a little delay, then tripped mains.

This suggests to me that the element is shorting to earth, a dangerous situation that I wish to avoid. The element has no earth terminal, so I think it must be shorting to the casing via the mounting screws. I've ordered a second replacement to see if it's just a faulty element, but is there anything else I should be checking?

 

[PrenticeBoyofDerry]

Have you done any electrical test to prove that the element is not faulty and there is no pathway to shorting to the casing?
Are you sure that it was the original element that was causing the earth leakage trip?

 

[yardie]

Could be the new element faulty, unlucky! But it does happen.

Whats the make & model of oven?

Sure theres only one oven element??? Sometimes one in the base as well as at the back near fan.

 

[Johnking]

Have you done any electrical test to prove that the element is not faulty and there is no pathway to shorting to the casing?
Are you sure that it was the original element that was causing the earth leakage trip?

Paths to earth can only be through the metal mounting plates. OK when cold, can't measure safely when got.

Old element clearly failed, big split down one section, it tripped the mains once when it failed, then never got hot again (I only noticed it was gone an hour later when the oven was cold - fan had been running all that time).

 

[Johnking]

Could be the new element faulty, unlucky! But it does happen.

Whats the make & model of oven?

Sure theres only one oven element??? Sometimes one in the base as well as at the back near fan.

Neff U1710. Horseshoe shaped element. I did, I admit, pay only 5 pounds for the new element. I don't think there is another one - just from looking at spares listings.

 

[PrenticeBoyofDerry]

Have you the ability and equipment to test the new element, they do sometimes turn up faulty, even from new, but you need to test it to eliminate or confirm the fault.
I do not thing the NEFF U1710 elements are too expensive even though £5.00 seems a little cheap and not so cheerful. Was it an untested ebay special???
I recommend buying genuine unused parts!

 

[Johnking]

Have you the ability and equipment to test the new element, they do sometimes turn up faulty, even from new, but you need to test it to eliminate or confirm the fault.
I do not thing the NEFF U1710 elements are too expensive even though £5.00 seems a little cheap and not so cheerful. Was it an untested ebay special???
I recommend buying genuine unused parts!

The only equipment I have is a simple multimeter. But it only faults when it's getting hot, I can't safely measure any resistance then. My guess is that heat expansion is causing some connection to be made. One thing I did notice is the element touches the case where it passes through the case due to poor manufacturing, but I thought the coating on the element was non-conductive. But if it is slightly conductive, perhaps it is enough to trip the sensitive rcd?

I've done a pragmatic test by ordering a slightly more expensive replacement, if that one works I will send the first one back for a refund. If not I will have to conclude there is another fault outside of my ability to fix it.

 

[Johnking]

Update: second replacement element gives exactly the same problem...heats up for about 30s then trips the mains.

Any thoughts? It's a very old oven, maybe time to replace it?


Found this on another forum, I'm going to try baking the element in the top oven...

When installing kitchens these days I often tell the client that the oven may trip the RCD and to call me if it does. I believe that is because of damp in the elements, as Alan says, whilst being stored in the warehouse.

However, I've never had one trip the RCD as soon as it is connected. Normally it would happen a minute or two after switching on the oven.

 

[jj4091]

Disconnect the element & insulate the wire terminals & then try again if it still trips then you definitely have a wiring or other component fault rather than a faulty element.

 

[PrenticeBoyofDerry]

could be the fan motor

 

[Johnking]

Baking the new element in the top oven did the trick, so I think the damp hypothesis is supported! I gave it about 30 minutes at 180°C.

Thanks for all the help.