Discuss Large oven tripping RCD in the Electrical Forum area at ElectriciansForums.net

al1981

New EF Member
Messages
1
Location
Lincolnshire
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?
 

Lucien Nunes

Respected Member
Messages
2,822
Location
London / Tallinn
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?
 

Joseph staniforth

New EF Member
Messages
2
Location
Rotherham
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.
 

Marti

Electrician's Arms
Messages
232
Location
Romford Essex
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!
 

Wilko

Electrician's Arms
Messages
5,385
Location
Berkshire
Hi - those cookers are recommended by manufacturer to be on an rcbo as they expect 8mA leakage. Perhaps confirm if this is the problem by turning off any other circuits using that RCD.
 

Pete999

Forum Mentor
Messages
21,801
Location
Northampton
Call an Electrician in to take a looksee at the problem
 

DaveChase

EF Member
Messages
16
Location
Hampshire
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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Taylortwocities

Electrician's Arms
Messages
2,218
Location
Oxfordshire
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.
 

Pete999

Forum Mentor
Messages
21,801
Location
Northampton
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?
 

telectrix

Scouser and Proud.
Respected Member
Messages
60,287
Location
cheshire/staffordshire
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.
 

Pete999

Forum Mentor
Messages
21,801
Location
Northampton
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.
Yeah me as well but I was being or trying to be diplomatic.
 

Jim Cartledge

EF Member
Messages
6
Location
Warrington
As an RCD is a current operated device, why would the 'power factor' have anything to do with it tripping? The power factor is related to the cosine of the angle between the voltage and the current.
 

Pete999

Forum Mentor
Messages
21,801
Location
Northampton
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.
College notes?
 

Dustydazzler

Regular EF Member
Messages
1,014
Location
Surrey
Technically speaking 6mm cable of a 50a mcb is a no no , it either needs to be 10mm or reduce the mcb to a 40

But I have seen an experiment done by J.W where he gets some 1.5mm clipped direct cable to draw very near 70 amps for a considerable length of time before starting to smoke.



Back to the OP , my single build in oven has the strange tendency to trip my house rcd from Time to time
 
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Pete999

Forum Mentor
Messages
21,801
Location
Northampton
As an RCD is a current operated device, why would the 'power factor' have anything to do with it tripping? The power factor is related to the cosine of the angle between the voltage and the current.
An RCD operates on earth leakage, Jim, it is not an OCPD!
 

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