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al1981

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Hi all.

Looking for a bit of advice.
Customer has a new large induction rangemaster cooker with a total power of 14.8kw.
Currently on a Hager board with a 50a b mcb and an existing 6mm cable.
As soon as oven was switched on it tripped the RCD.
Taking diversity into account the cable should be fine.
Is the breaker too large?
Insulation resistance test comes back fine.
Should I try a smaller breaker?
The oven has the potential to pull 60 + amps and they’ve said they want all 3 ovens on and the hob so I’m wondering if it needs it’s own 63a RCD and a 10mm?

I don’t want to stick it on a 40a and have issues later on.
I guess there’s also the potential that the element had gone as well?
 
As soon as oven was switched on it tripped the RCD....
Insulation resistance test comes back fine.

Numbers please! Sheathed heating elements that have stood around sometimes leak badly until they have been baked out, but this would show as very low insulation. So it's possible the insulation test did not actually test the elements, if there are relays in the control circuit that might have isolated them. It has been known for elements to need baking off the RCD until they come up to spec.

What is the RCD serving? Much of the installation i.e. may be near its limit anyway?

Is the breaker too large?... Should I try a smaller breaker?

Eh?? What has OCPD rating got to do with leakage?
 
Is it a new oven? Have this problem a lot with new kitchen installs, the ovens are stored in cold warehouses, condensation on the metal can cause continuity between line/earth
A lot of the time they send their engineers out who advise the cpc is disconnected to allow the oven to heat up and get rid of condensation, I always advise how dangerous this is and suggest to the customer they insist on a replacement.
 
Does this happen with anything / everything else on the board on? Could be the major leakage is elsewhere but 5 - 10 miliamps earth leakage from the oven is enough to hit the limit of a 30mA RCD. What 's the ramp test for the RCD? Finally, does it happen with the oven empty? I had one that tripped only when cooking, never testing and the moisture was shorting the oven. Raising the temperature slowly dried out the internal surfaces and it was fine!
 
It sounds like the RCD tripping is the only thing stopping the 6mm cable from melting at the moment.

Whatever the issue is (& I'm inclined to agree that the oven is probably tipping the balance with the real fault being elsewhere) it's lucky it did trip as it could have just prevented a much more serious situation!
 
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Yes figures on the IR test. And test the appliance too. In fact, do that first. After you have corrected the MCB size on that circuit.

Oh hold on. If you are a trained electrician, you really need to check your college notes. You have forgotten some essential basic things.
 
exactly that ! being a large inductive load, it would have an effect effect on power factor, and if power factors get too high, they can trip the RCD.
So you are saying that if something has a near unity PF it can trip an RCD?
 
think he means if the PF is below unity, e.g.0.8 or less. i'd like to know why it might cause rCD tripping though. in this situation, I'd shift the oven onto a 40A RCBO and see if it held.this would eliminate cumulative leakage.
 

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