Help! . . . . another oven problem

[vickery1971]

Hi Guys,

I was hoping a few of you 'learned ones' could offer some advice. I have just been to first fix a kitcken, all looked ok with a few sockets to move, the lady has two 3kw smeg ovens, my plan was to use the existing 6mm radial with an isolator and a twin cooker outlet so i thought all was well. The lady then decides to bring out a 1.5kw steam oven and a 3.4kw microwave. All these appliances wil be inset and sit in a block of 4.
I first thought about new radials but its a concrete floored house, laminate floor upstairs DB in the garage on the other side of the house, . . . . all of a sudden the job became a pain in the bum!

So, is there any way i can wangle it, obviously i can only have two of the appliances on the cooker radial, is there any way i can put one of the ovens and the steam oven on spurs on the ring?

Any advice would be greatly received,

Thanks

Ian

 

[telectrix]

the steam oven should be OK on the RFC, but the microwave will need it's own circuit, IMO. btw, you have poached lenny the moderator's avatar.

 

[trev]

Best change it mate, you don't want to incur the wrath of Mod

 

[Engineer54]

Never seen a 3.4KW microwave oven, biggest i've seen is around 1KW!! Are you talking about a combination microwave oven?? If you are, then you'll never see the full 3.4KW!! They are again indicating connected KW rating, not the Max working KW rating....

 

[vickery1971]

Oh no, ive had that avatar since i joined . . . . is Lenny a big bloke? . . . . and does he have my address . . . lol

I will change it to avoid a fight!

 

[vickery1971]

Now please dont tell me Jack Hargreaves is a moderator?

 

[Badged01]

This something to get your teeth into!! I wouldn’t call myself a “learned one” or even a particularly “wise one” for that matter but my thoughts would be …..

Existing 6mm radial should be able to take a 32A breaker if the method of installation etc …. hasn’t derated the cable and of course the voltage drop is OK! Assuming that’s all fine a cooker circuit may supply two or more cooking appliances as long as they are all installed in the same room and have the cooker control switch within 2 metres of them. (i.e. you can put the SMEG’s and steam on the existing cooker circuit in the housing. If all appliances are on 13A plugs then could you not extend the cooker radial from control unit and have FCU’s/sockets for them all in the housing?)

All three of these pull just over 32A so provided shes not running a cooking business from home at full blast throughout the day I’d apply diversity to the three cookers on the circuit! If the cooker control unit doesn’t have a socket outlet then two SMEG cookers & steam oven gives just over 28A (worst case of 10 amps + 30% of remaining load for each cooker). Demand wise all 3 could sit on the existing 6mm cooker circuit.

That leaves the microwave (3.4kW/15A ) which as said in an above post I would suspect is a micro/grill combination unlikely to see full power!. If a separate circuit is not going to be viable with the customer because extensive work is required(?) there is potentially a practical work around solution if there is a dedicated kitchen socket circuit (2.5mm T&E on 32A breaker?). Dependent upon the microwave manufacturers connection instructions and the existing loading on the circuit you could connect to the kitchen socket circuit with a switched spur – a typical kettle which runs at 3kW(13A) is already able to be plugged into the same circuit!. ( Whilst appendix 15 of the regs advises appliances over 2kW to have their own circuit this is not a regulation but for guidance and interpretation in meeting the regs if required. For me this means depending on the individual circumstances as I would apply in this case -- rules are for fools or the guidance of wise men as my old lecturer would say!)

Logic here is the customer has a dedicated kitchen socket circuit so can control how many appliances are on at the same time to avoid tripping the MCB – i.e. kettle, toaster, dishwasher, washing machine, microwave etc …... I would also do a little calc to determine the demand of the circuit and if the breaker can be derated to say 25A so as to provide further protection of the cable against small overload current over a long period!

Of course if you haven’t got a kitchen socket circuit, or if the customer is not happy with this practical workaround, then its probably impracticable and I cant see anything other than a new radial circuit. If you have to do this you may as well run another circuit(s) for the cookers!.

Depending on installation method, volt drop etc .... there is another argument that the 6mm cable could actually be rated at a higher current than 32A (upto 47A?) and hence a greater circuit breaker could be used and possible the microwave could be incorporated on the circuit as well -- I havent the mental apptitude to think that through. Thats where more learned forum member could advise practical reasons for/against!!

Only other thought I’d have is if these cookers are on the same RCD the earth leakage may trip the RCD? Cookers can have high earth leakage currents but you will need someone with more knowledge to advise you.

Hope thats provided some food for thought/debate ............. hard hat on I'll await the responses!!

 

[vickery1971]

Oh, and back to the oven problem, Yes it is a combination microwave, just looked on the Smeg site and it says 1kw mocrowave, Nominal power 3.4kw. All i need now is a couple of plate warmers and a convection hob!

 

[vickery1971]

Thanks for the reply, that makes sense, i didnt realise you could have more than two appliances on the cooker circuit, and i agree with the diversity angle of the microwave never pulling 15A (Smeg website says the microwave can be limited to 2kw if needed, but doesnt say how, and instructions with the appliance are basic) . . . . but thats a start!

The customer isnt really bothered about rules, im just doing it for my own peace of mind, added to that the rest of the house is a bit of a cowboy job so im being careful.

Cable run is about 15-18m and from what i can see its clipped direct, through an uninsulated floor void.

Ive had about five kitchens this year were customers want half a dozen ovens, what ever happend to a good old counter top baby belling!

Thanks for the advice mate, i hope you dont get torn apart by the learned ones . . . .

 

[trev]

Now please dont tell me Jack Hargreaves is a moderator? [/QUO
Yeah you're right, Lenny is HUGE! and a bad tempered bugger too. Don't even think about messing with Jack mind you, since he retired he's got loads of time on his hands so he can track your IP address then come round to kick your butt