Double oven and induction hob connections

[mrkjd]

We are planning a major kitchen refurb and want to spec the electrics for a 5.5kW double oven and 7.4kW induction hob. Initial thoughts are to run a seperate circuit in 6mm T&E from the CU ON 30mA RCBO to a Click 45amp Dual Appliance outlet plate (approx 5m cable run in loft and behind kitchen tall cabinets). Then 6mm T&E from the outlet to seperate 20amp DP isolators from which I need to run flexible butyl cable to the appliances (MIs stipulate this and don't want them to dodge any warranty issues by claiming incorrect cable used if we just use T&E). The rest of the kitchen electrics will be wired into another seperate gang on the CU (extractor/fridge/washing machine/outlets) and the lights remain on the existing lighting circuit.

Do I need 6mm for the 2 cables from the outlet plate or would 4mm suffice? Instead of having seperate 20amp isolators could I have a single 45amp DP isolator before the outlet to cover both appliances? What size butyl cable would I need - was thinking 4mm but maybe 2.5 mm would be sufficient as I'm not sure if 4mm will easily fit in the terminals.

 

[ban-all-sheds]

We are planning a major kitchen refurb and want to spec the electrics for a 5.5kW double oven and 7.4kW induction hob. Initial thoughts are to run a seperate circuit in 6mm T&E from the CU ON 30mA RCBO to a Click 45amp Dual Appliance outlet plate (approx 5m cable run in loft and behind kitchen tall cabinets).

Your electrician will be best placed to discuss circuit options with you.

Then 6mm T&E from the outlet to seperate 20amp DP isolators

Cooker outlet plates are meant for connecting appliance cables, not as a stage in fixed installation wiring.

Do I need 6mm for the 2 cables from the outlet plate or would 4mm suffice?

Your electrician must be the one to decide that.

Instead of having seperate 20amp isolators could I have a single 45amp DP isolator before the outlet to cover both appliances?

What do you want?

What size butyl cable would I need - was thinking 4mm but maybe 2.5 mm would be sufficient as I'm not sure if 4mm will easily fit in the terminals.

What do the MIs say?

 

[winston1]

6mm, or probably 4mm OK, from CU to 45 amp double pole isolator (if you want it, as isolator is not required), same cable to dual appliance outlet plate, then your butyl cable to the appliances. 2.5mm will do, you won't be running the induction hob at full tilt will you? In fact I doubt if it will let you.

I hope this is more useful than that pointless post from BAS.

 

[mrkjd]

Thanks Winston1 - very helpful. Will ensure 6mm used. I thought a cooker/hob/oven had to be isolated from previous posts I'd read, just wasn't sure if you could treat a seperate oven /hob arrangement as a "cooker" so use a single isolator. Seems prudent to have something in the event of an emergency so think I will spec for the 45amp DP isolator as you suggest. Is the 30mA RCBO at the CU OK?

I wasn't sure if 2.5mm butyl would be sufficient even with diversity applied as the MIs make no mention of cable thickness - just that it must be flexible and heat and oil resistant. I have read several posts about this requirement being over-restrictive and T&E being perfectly adequate but the warranty implications of using T&E worry me as domestic appliances these days can tend to have variable QC.

As for usage, Xmas dinner is often mentioned as the maximum scenario but we occasionally have a "team fry-up" for extended family /friends which might see 3 rings going full pelt for 20 mins or so which I think might load the hob more. More typically just the 2 rings in use for a midweek spag-bog or similar!

 

[ban-all-sheds]

I hope this is more useful than that pointless post from BAS.

My post was not pointless.

Did it go over your head, perhaps? Was the problem that it was too hard for you to understand?

 

[winston1]

RCBOs have 2 ratings, the overload rating and the residual current rating. The 30mA you refer to is the residual current rating. The overload rating with your proposed setup would be 40 amps.

 

[JohnW2]

As for usage, Xmas dinner is often mentioned as the maximum scenario but we occasionally have a "team fry-up" for extended family /friends which might see 3 rings going full pelt for 20 mins or so which I think might load the hob more. More typically just the 2 rings in use for a midweek spag-bog or similar!

Even when, from your point of view, 3 rings are going 'full pelt' they will all actually be cycling on and off by virtue of their thermostats. The average load over a significant period of time will therefore be less than you imagine.

Kind Regards, John

 

[mrkjd]

Thanks John

 

[mrkjd]

Was all set to run with 6mm all the way thru to the 5.5kW oven and 7.6kW hob splitting to 6mm from the dual appliance outlet to each appliance but an electrician I was chatting to says for the combined load of 13.1lW I need to run 6mm cables seperately from each appliance to separate RCBOs on the CU! Is this correct?

 

[EFLImpudence]

No, it's rubbish. Tell him to get another job.

 

[EFLImpudence]

Was all set to run with 6mm all the way thru to the 5.5kW oven and 7.6kW hob splitting to 6mm from the dual appliance outlet to each appliance

4mm² will do from outlet to each appliance.

 

[ban-all-sheds]

Actually, 4mm² could well be OK for the entire circuit.

 

[EFLImpudence]

I didn't want to list all the options.

 

[mrkjd]

Thanks everyone. I discussed this all further with him. He has been installing 2x6mm with seperate RCBOs in new builds for a couple of years contract work. Seems they are not applying the diversity rule for domestic kitchens of 10amps+30%+5amps for any socket. If I remember the fag packet figures in our case diversity brings down the total potential load from 56 amps to 24amps as the circuit is to be dedicated with no other sockets, 6m to CU thru uninsulated stud and suspended floor. This means 4mm would do from the outlet but since routing is not too difficult in this case I think I will spec 6mm all the way. I am surprised diversity makes such a big difference but understand that full load conditions for an oven/hob is nothing like (for example) an electric shower. Perhaps more surprising is that new-build developers are installing 2 runs where 1 would do and not pruning the costs down!

 

[ban-all-sheds]

Perhaps more surprising is that new-build developers are installing 2 runs where 1 would do and not pruning the costs down!

Maybe they are being misled, and fleeced, by electrical contractors who don't apply diversity.