Cooker Cable Size / Wiring

[Ash4eva12]

Hi All

Just looking for a 2nd opinion on cable sizing / breaker for a old cooker.

The customer has had a 'Cooker Engineer' out to advise that the cooker needs to be wired in 16mm cable to a cooker switch which is currently unused.

The current setup is a 2.5mm HR flex on a plug top with a 13 amp fuse plugged directly into the kitchen ring main. Whilst i agree that it should be on a dedicated circuit rather than plugged into the kitchen ring I've got some issues with his recommendation of requiring a 16mm cable directly into a cooker switch.

Cooker in question (having confirmed with manufacturer) they state requires 'HO5RR-F cable @ 230V 3x 2.5mm2' with a maximum load of 19amps.

This tells me that 2.5mm cable would be adequate for the cooker & not requiring a 16mm cable as the 'cooker engineer' has stated?

Other issue is the cooker switch on the wall (not currently used) is wired in 6mm T&E connected to a 32A type B MCB.

Am i right in thinking that this could be utilised by doing the following ... Replacing the cable from cooker to switch for 'HO5RR-F 2.5mm2 3-Core directly wired into the existing cooker switch. Then dropping the MCB to a 20A to protect the cooker cable from exceeding 20A?

Any opinions on this would be great as at present is maufacturers vs cooker engineer vs electrician!

 

[pc1966]

As a "fixed load" the MCB only has to protect against a fault. So if your end of circuit Zs is OK for a 32A MCB and the load is below the lowest cable section's CCC then just leave it.

Some cookers have quite high temperature requirements, then the LSOH version of T&E (6242B) is an option.

But if they specifically suggest flexible cable like HO5RR-F or H07RN-F then use it. But I would say you should use ferrules on the cable ends to make for a robust and reliable termination.

 

[pc1966]

You might find the cooker can take 4mm cable and in that case you also meet the overload protection, though it is not needed here.

 

[Ash4eva12]

As a "fixed load" the MCB only has to protect against a fault. So if your end of circuit Zs is OK for a 32A MCB and the load is below the lowest cable section's CCC then just leave it.

Some cookers have quite high temperature requirements, then the LSOH version of T&E (6242B) is an option.

But if they specifically suggest flexible cable like HO5RR-F or H07RN-F then use it. But I would say you should use ferrules on the cable ends to make for a robust and reliable termination.

Hi

Thanks for the reply!

I agree with what you have said with cable type & size i think we stick with manufacturers guidance & agree the best way forward is with 'HO5RR-F 2.5mm2' as the manufacturers have stated (Not a 16mm2 that the cooker engineer has implied)

I also agree that ferrules should be used for termination ... we try to use ferrules on cookers / hobs when we can as good practice for better termination.

Only real issue with guidance was for the 32A MCB feeding a 6mm T&E from the consumer unit to the cooker switch... to then connect in a 2.5mm2 HO5RR-F from cooker to switch. Likewise the 6mm is fine on the 32A MCB but didn't know if the smaller cooker cable from switch to cooker would require protecting as the maximum Amps on the 2.5mm HO5RR-F is around 24amps therefore below the 32A of the MCB. As the cooker pulls 19Amps max. would it be good practice to drop the MCB to a 20A therefore protecting the 2.5mm HO5RR-F from exceeding the 24A if it ever did.

 

[loz2754]

Hi

Thanks for the reply!

I agree with what you have said with cable type & size i think we stick with manufacturers guidance & agree the best way forward is with 'HO5RR-F 2.5mm2' as the manufacturers have stated (Not a 16mm2 that the cooker engineer has implied)

I also agree that ferrules should be used for termination ... we try to use ferrules on cookers / hobs when we can as good practice for better termination.

Only real issue with guidance was for the 32A MCB feeding a 6mm T&E from the consumer unit to the cooker switch... to then connect in a 2.5mm2 HO5RR-F from cooker to switch. Likewise the 6mm is fine on the 32A MCB but didn't know if the smaller cooker cable from switch to cooker would require protecting as the maximum Amps on the 2.5mm HO5RR-F is around 24amps therefore below the 32A of the MCB. As the cooker pulls 19Amps max. would it be good practice to drop the MCB to a 20A therefore protecting the 2.5mm HO5RR-F from exceeding the 24A if it ever did.

Under what circumstances might the cooker exceed 24 amps?

 

[Ash4eva12]

Under what circumstances might the cooker exceed 24 amps?

I'm assuming the cooker is correct with specs we have been given as its over 15 years old with little information available. I agree a cooker should never exceed the maximum. The problem we have is were going on what the manufacturers have said via phone to what is their recommended requirements. To stop a overload on the cable from cooker to switch we was thinking of dropping the 32A MCB to a 20A incase the cooker did actually pull more than 19A

 

[loz2754]

You're free to do as you say if it makes you feel more comfortable, but the cooker is a fixed load and does not necessarily require overload protection.

 

[Ash4eva12]

You're free to do as you say if it makes you feel more comfortable, but the cooker is a fixed load and does not necessarily require overload protection.

Thanks both for your input. Sounds daft i know but we got the feeling on the phone that the manufacturer didn't have a clue either even though they manufactured the appliance 15 years ago. From experience I've found it depends who is on the other end of the phone to whether you get the correct answer!