Cooker circuit sanity check please.

[Bobble23]

Hi,

Just been scratching my head about this one and wonder if I've missed anything.

A few weeks ago I installed a new circuit for a 3kw oven and a 950W microwave. Ran the circuit in 6mm T&E clipped direct on a 40A RCBO.

Customer has reported that on maybe three or four occasions the RCBO has tripped when the oven's been running for forty minutes or so. Microwave wasn't running when it tripped.

I've been back a couple of times and all my terminations seem fine, and the IR test on the circuit is >500 megaOhms on each test, as it was when I put the circuit in.

It's a brand new oven, but the customer got the Bosch engineer out anyway to check it and was told there are no problems (although I don't know how long he ran it for to work this out).

The only other thing I can think of is that I had a faulty RCBO, so I went round yesterday and swapped it for another one.

Any ideas if there's something else can be causing this?

Thanks.

 

[littlespark]

Can the microwave be isolated (neutral as well) while it’s not being used to see if the tripping continues.
If that solves it, more likely micro at fault. Remember it doesn’t have to be turned on if there’s an N-E fault…..

Have you checked for moisture in or near either appliance?

Did you ramp test the RCBO? Might just be overly sensitive and not actually faulty.

And at a long shot…. Is there a smart meter in close proximity to the RCBO?

 

[Bobble23]

Thanks littlespark.

The microwave's brand new too, so I'm guessing not the culprit, but it can be easily disconnected if it happens again.
No moisture anywhere near any of them, and no smart meter (but out of interest have they been known to interfere?).

Good call about the ramp test. That didn't occur to me and is now too late (I've replaced the RCBO), but I'll certainly do one if it trips again.

Thanks for the help though.

 

[littlespark]

It’s not a proven interference… but there has been anecdotal evidence on the forum where smart meters have tripped RCDs… a metallic shield between the devices being suggested as a solution.

 

[davesparks]

Have you been able to recreate the tripping?
Have you measured the earth leakage and load current?

 

[Bobble23]

No, it only ever trips when the oven's been on for a long time and I've not been there then. I'm hoping changing the RCBOmight have worked but I'll let you know if it goes again and I find anything.

Thanks for all your help.

 

[James]

It might be worth asking the customer to turn the oven on 45min before you arrive.
then do an IR test on the oven from the isolator with the oven switched on and the stat set to max but the isolator off.
incase the element is breaking down when hot.