Cooker hood tripping RCBO - head scratcher

[Octopus]

MFT calibrated - EL clamp meter six months old. RCBO's ramp tested (25mA -27mA) Even though RCBO's were new swapped for new ones.

Murdoch - I'm looking believe me but trying to understand the science behind it.

Mate, of the leakage is low on 1 leg and an extension, but high on the other............

 

[Richard Burns]

I think you have proved the theory quite well with your testing!!:smile5:
Put a nice tightly wound coil of cable behind the socket, problem solved, though possibly causing other problems!:sick:

80m of ring on a 2 bed bungalow sounds quite high really, and if you are testing on a 2m length then on a 78m length there is a major difference. Though the extension lead is a smaller change, but possibly higher resistance joints.
The only other thought would be a loose connection arcing somewhere, but with all the changes you have made this sounds unlikely.

Take all the covers off the cooker hood and put tape around any metal where the motor /fan rotates and see if the tape gets scraped when it runs.

@Richard - was thinking along those lines though I'm not aware of the method to prove this theory - ring circuit tests were r1 0.63 rn 0.57 & r2 0.97 - average 2 bed bungalow so around 80 square meters.

Trouble is I know when the Bosch engy comes out he will say it works on one socket so must be 'lectrics'!

 

[Rob190]

yeah, I know mate. So as above replaced short leg 2M with IR tests of > 900 Meg - no other circuits connected in board.

Duplicated fault on cooker ciruit with similar length.

So if the longer leg is absorbing 70mA it doesn't compare with other faults I have dealt with such as leakage on a long ring from garden supply?

Appreciate the help & will atke it on the chin if i am missing the obvious!

 

[Rob190]

@Richard

Yeah, pretty straightforward now at home - straight 2M run to board = trip, longer run = no trip.

Would open hood up but will leave it I think until Bosch have had a look.

These faults are sent to test us lol.

 

[Lucien Nunes]

if the longer leg is absorbing 70mA

I don't buy this. A longer cable won't make 70mA of leakage 'disappear', that's enough to run a 15W lamp. If the leakage from the hood were from L-E then it's going into one of two cores at almost the same potential - the leakage added by the cable's capacitance L-CPC will be hundreds of times more than that removed by the capacitance N-CPC. In any case, when the long and short legs are both connected the RCBO wouldn't trip.

Much more inclined to think it's an N-E fault. Then with the short cable it's much lower resistance and diverts more current. In that case the 70mA is probably quite arbitrary and you will tend to get different numbers with different loads on elsewhere.

Suppose there is a stock fault on the hoods that causes N-E fault on high speed? Have you tested the hood leakage on high speed when isolated from the outside world, e.g. PAT with it sat on the worktop?

 

[Richard Burns]

I don't buy this. A longer cable won't make 70mA of leakage 'disappear', that's enough to run a 15W lamp. If the leakage from the hood were from L-E then it's going into one of two cores at almost the same potential - the leakage added by the cable's capacitance L-CPC will be hundreds of times more than that removed by the capacitance N-CPC. In any case, when the long and short legs are both connected the RCBO wouldn't trip.

Much more inclined to think it's an N-E fault. Then with the short cable it's much lower resistance and diverts more current. In that case the 70mA is probably quite arbitrary and you will tend to get different numbers with different loads on elsewhere.

Suppose there is a stock fault on the hoods that causes N-E fault on high speed? Have you tested the hood leakage on high speed when isolated from the outside world, e.g. PAT with it sat on the worktop?

I was thinking it was a short duration fault (<10ms) as the motor rotated that could be just "smoothed" enough on a long cable rather than a short one, though as you say it should not then happen on the fully connected ring.
However I would agree with the NE fault, but this would be dependent on current drawn and should have shown up on running a kettle, etc. unless it was only present at high fan speed.

 

[Leesparkykent]

PAT the cooker hood.

 

[Octopus]

PAT the cooker hood.

like you would a dog on the head???

 

[Leesparkykent]

Haha yeah only if he's been good though :teeth_smile: ^^

 

[Rob190]

Don't do PAT testing but did clamp the hood CPC that spikes on a short cable.

Will update with the findings of the bosch guy.