# Forum Home Renovation Kitchens  Wire in Oven and separate cooktop

## kiter

Hi 
Any sparkies out there? 
I am putting in a separate oven and cooktop. The oven rates as  0.99kwh  and cooktop as 7kwh. In the instructions for the cooktop it recommends  3core 2.5mm cable. (seems low to me).
There is an existing cable (4mm) from the Consumer unit with 30a trip. I  will be running from here to an Oven switch (clipsal 30a oven), then  down to a junction box where it will connect to the oven and cooktop.
Now in the uk it is preferred to use 6mm cable, but I am guessing not in  Oz? I came across an old copy of the AUS/NZ wiring regs and they state  only 4mm for an "oven and/or cooktop" 
Just wondering how are you supposed to get both cables into the oven  switch? the terminals seem too small. The uk switches have two sets of  terminals one from the mains and one to the load, but here they all go  into the same terminal it seems? I know it's bad practice to juts shave a  few strands back of each cable, but how else do they fit? (not actually  tried yet, it just looks small).  
thanks for any help

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## chalkyt

You have a few issues running around. 0.99kwh (kilowatt hours??) for the oven. Is it 9.9 kilowatts (41 Amps)?. Similarly I guess that the cooktop is 7.0 kilowatts (29 Amps). Both are pretty BIG for a domestic situation. 
AS3000 (the "Wiring Rules" 4.7.1) requires that the hotplates have a separate switch mounted near but not on the appliance. This does not apply to an enclosed cooking appliance such as a built-in oven.  
2.5mm cable is rated at 27A i.e. less than the individual loads of your oven and cooktop. 4mm cable is 37A, still not big enough for the oven if your above ratings are correct. 
Might be worth spending a few bucks on your local friendly electrician in order to get it right, or ask the Electrical forum to have a look here and put in two bobs worth.

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## kiter

thanks chalkyt,
i couldn't find the actual power rating for the version of the oven in this country, so had to take an equivalent. I have since found it - 13amp.  The cooktop is 7kw  (kwh was a typo).
Yup definitely think the 2.5mm is too small, and when i questioned the manufacturer - Evedure, they refused to comment (pretty poor if you ask me).

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## chalkyt

Those numbers seem to be a bit more normal, although the oven now seems to be a bit low (ovens are typically around 4.5 - 5.0 kW). Evedure should at least be able to tell you what current rating cable they recommend. 
Generally for a single phase supply, there are two A - N circuits (one for the cooktops and one for the oven) or one big A - N circuit (6mm or 10mm), or two actives and a neutral if it is across a two or three phase supply. If you don't have this then your local friendly electrician still has a job to do. As things stand you need 30A for the cooktops and 13A (maybe 21A ???) for the oven i.e. at least 6mm flexible cable cable to the appliances.  
Your existing 4mm supply is probably derated from 37A unenclosed to 26A since there is a fair chance that it spends a lot of its life in conduit or surrounded by insulation (see AS/NZ 3008 Table 9 or Chrisps simplified cable ratings in the library, although i haven't been able to successfully open this). 
So,there you have it. One circuit for the cooktops with a separate switch as per AS/NZ 3000 "Wiring Rules" 4.7.1 and another circuit for the oven. Each circuit and its circuit breaker needs to be of sufficient size to supply the rated load of the appliances since when the cook is in hyper mode, all the elements could be on at once.

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## kiter

thanks, I had come to this conclusion as the oven turned up with a  13a plug on it. (In the Uk it's possible to just have a 13amp fused power outlet run from the same cable to the consumer unit which then downgrades the protection to 13amp instead of 32amp at the MCB.) The problem I now have is that there is not room for another MCB in the consumer unit. I could run a spur from an existing power outlet (which dishwasher is plugged into), but I am concerned this will be too much load and will keep tripping the MCB. There are two MCB's for power outlets (this is a unit), so first i need to see which ones are on each, but there is only one that i can really run a spur from.
If this is not an option, is there an alternative to getting a sparky to fit a whole new consumer unit - is it possible for them to create a separate one for the oven, or would the cost be about the same? i want to do as much of the wiring/cutting out walls as i can to reduce the cost/time (and i can install rest of kitchen units) so the sparky can just do connections.

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## chalkyt

It is not uncommon to fit a separate sub board adjacent to the existing one (if there is room in the cabinet) with the stove MCB on it, and if the circuit arrangements are suitable, swing your other kitchen circuits onto it as well (e.g. kitchen GPOs) just to keep things logical and tidy. Another option is to run sub mains (or use the existing stove circuit for this purpose if it is big enough ( talk to your electrician about this) from the main board to a new kitchen sub board. 
I was always bothered about someone "helping" by doing the wiring for me to use. I usually spent more time checking that it was OK than I would have done doing it myself. The best way for you to help the electrician is to drill the holes in plates, studs and noggings and run a draw wire for him. If you do this, make sure that the cable can be pulled in easily with no bends, runs are straight and easy to get to and the holes are big enough to fit several cables through and are in the centre of the timber (AS3000 requires that cables are free to move and are 50mm from the wall surface i.e.90mm stud plus 2x10mm gyprock puts the centre of the stud 55mm from each surface = OK). This will reduce his labour and make "3/5 of bugger all" difference to the cost of cable etc.

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