Oven OPD advice

[Phoenix]

I'm fairly sure I'm on the right track here but would appreciate any thoughts...

Working on a kitchen re-furb whereby the old cooker was a free-standing range. The isolator was hidden behind the old units so a new 6mm radial supply has been provided with an above the worktop DP isolator / socket and 32A MCB. The load side of the supply has not yet been terminated to a ccu until the new cooker arrives. So far so good and all plastering and painting has been completed.

Units and appliances have arrived and the cooker has been changed...it is now a built-in oven unit with a gas hob. The oven 'instructions' are crap! The Chinglish label on the appliance states 230v and 2870 kW (!) assuming this is a typo that gives a max demand of 12.5A...there are NO recommendations regarding supply so at least I can't fail to comply with MI's! The supplied power cord seems to be about 1.5mm

Any fuse I fit obviously needs to be accessible and this unit is so deep there isn't room for a CCU behind it. There is no way further chasing / re-decorating will be entertained so another above the counter FSU is out of the question. I'm thinking of doing the connection in a JB behind the removable plinth. I think I could use 433.3.1 here and do away with overload protection, except for the 1.5 metre or so of terminal cable to the oven! but I also have a 16A mcb I could install in place of the 32A one, which would also protect the smaller cable.

As I see it by using the lower mcb I am affording SOME overload protection rather than rely on the 32A one and all protection & isolation devices are accessible. The connection below the units IS accessible for testing / inspection purposes.

As well as getting an answer I also get rid of the 60 day thing!

 

[Geoffsd]

I think I could use 433.3.1 here and do away with overload protection, except for the 1.5 metre or so of terminal cable to the oven!

433.3.1 would apply to the oven cable if it complies regarding fault current protection.
The 6mm. doesn't need it.

but I also have a 16A mcb I could install in place of the 32A one, which would also protect the smaller cable.

That would seem to be the easiest option.

As I see it by using the lower mcb I am affording SOME overload protection

Why do you say 'some'? Is the oven flex not rated at 16A?

 

[Phoenix]

Why do you say 'some'? Is the oven flex not rated at 16A?

Yes, it will cope with 16A, what I meant was, the max demand is 12.5A so would that not indicate a 13A supply, or is 16A close enough?

 

[Geoffsd]

You are mixing up two methods.

The MCB is there to protect the cable.
So if the flex can handle 16A then all is well.
In that case, with a 16A MCB, you are not omitting overload protection because it is there.

However, the oven at 12.5A cannot overload the circuit so it doesn't matter what size the MCB is as long as the flex can handle the current in the event of a fault to earth.
This is determined by using the adiabatic equation.

 

[Phoenix]

Thanks for clarifying that.

 

[Engineer54]

How can a fixed load be subject to overloading anyway?? lol!! That's without taking in to account that the manufacturer's load rating, is the connected load and not the actual max load, which will be lower...

 

[HappyHippyDad]

Your 1.5mm cable will have a CCC of 19.5A so the 16A MCB will be fine, however it looks like you also have a socket attached to the DP switch so you could get some nuisance tripping if they choose to have a microwave or something similar plugged in which takes a fair bit of power. Also I would look at the manufacturers instructions on what they ask for with regards 'overload protection', I know you've said its difficult to read but they must have that somewhere.

Also I cant work out why you have to have a junction box rather than a cooker outlet plate channelled into the wall behind the cooker? It wouldn't take long to channel it and it will only poke out approx 2cm's (if channelled not surface mounted).

 

[Jimmyb]

I would just leave the 32a mcb in the cu and connect oven straight into the outlet plate as it dosent need overload protection and the mcb will protect the cable for sc, but also connect a meter or two of flex to the outlet plate with a trailing socket to connect the gas hob with a 3amp fuse as man instructions.

We always install 32amp 6mm cable to outlet plate then connect electric hob and oven straight to the outlet plate.

If your still worried just use a double trialling socket and plug oven in aswell, I know its not how it should be done but it would be safe but like I say I would just connect oven without