Installing new oven and cooktop

My existing electric range is rated at 8500 watts, although that does not include anything plugged into the two power points on the stove (e.g. a 2300 watt jug, not that I do that). The power point on the wall and the plug are rated at 30 amps, and the circuit breaker 32 amps.
I have a new cooktop rated at 6400 watts and a separate oven rated at 2900 watts. Is it OK to plug the oven into the cooktop, and run a humungous cable to the power point?
I will never use all the elements at the same time. If anyone does that the circuit breaker will trip, just like it would have with the old oven (but it never did).
An electrican has said that I will need a new power point for the oven, even though the new and old arrangements use almost the same maximum amount of power.
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On 19/09/2011 06:55, Matty F wrote:

In reality its highly unlikely it would - even if you turned the whole lot on at once. The thermostats would kick in and drop the load before the circuit breaker had a chance to complain. (they take some time to respond to overloads. See:
http://wiki.diyfaq.org.uk/images/d/d4/Curve-MCBTypeB.png
A 32A breaker will let you have 45A almost indefinitely, and even 50A for 1000 secs (over quarter of an hour).

Not being intimately families with your wiring regs, I can only give guidance based on what we would do here...
I had a glance at:
http://www.energysafety.govt.nz/upload/33458/ecp51v18.pdf
Which seems to suggest similar sized circuits are the norm, although the connection methods differ and the terminology is a bit different.
We would not normally connect the cooktop (I presume what is we would call a "Hob"[1]) via plug and socket, but would hard wire it to a "cooker point"[2] (basically a termination box with a big red switch, and facility to clamp the cord to the hob / cooker (sometimes with a built in socket as well)).
Hobs here would not have any additional sockets on them.
Cookers in general are treated with a significant allowance for "diversity":
http://wiki.diyfaq.org.uk/index.php?title=Diversity
In other words a recognition of the fact that the typical pattern of use combined with being thermostatically controlled, its is very difficult to draw anything like the theoretical maximum current for anything but very short durations. Since circuit breakers permit short term overloads, and the cable is adequately specified, its permitted in a domestic environment, to connect even quite substantial cooking equipment with a maximum load of up to 15kW to a 32A circuit. The patterns of use and the thermostats, typically mean that even a 6kW hob will rarely draw more than 20A.
Hence we would compute the effective demand as 10A + 30% of the remaining maximum load (+5A if a socket is provided on the cooker point).
So in your case 6400 + 2900 = 9300W or 40A
The diverse load being 10 + 30% of 30 = 19A - so the circuit is fine for feeding both devices. The only question then remains how to connect them. That bit I can't really answer, since practice there is different. With smaller ovens here, they are often designed to plug into a normal 13A socket since their load is often in the 1800 to 2200W range. Yours is 2900 which suggests a double oven perhaps. I would expect that you need a suitable socket of flex connection unit for the oven and possibly a second one for the cooktop depending on the terminal capacity.
[1] Typical electric hob in the UK:
http://www.tlc-direct.co.uk/Main_Index/Domestic_Index/Baumatic_Hobs_Electric_Index/Baumatic_Appliances_Hobs_Elec/index.html
[2] Cooker point:
http://www.tlc-direct.co.uk/Main_Index/Wiring_Accessories_Menu_Index/White_BG_Index/Cooker_and_45Amp_Switches_3/index.html
--
Cheers,

John.

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On the wall is a large socket and switch, and I have the large plug and wire from the old stove. I was proposing that the large wire can go to the cooktop. Since the new cooktop is directly over the oven it's effectively one unit which could be wired together. I was thinking it would be nice to be able to have a plug on the oven wire in case the units have to be separated for maintenance, but maybe it could be wired in permanently as that would be more reliable. And cheaper too!
In my job I do deal with currents of several hundred amps, and in an earlier job I designed and made transformers using up to 5000 amps. But I'm not up with current house wiring idiocy ^B^B^B^B^B^B regulations! (What is the command to denote Rub Out?)
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I have been pursuaded to have an extra 15 amp socket installed in the wall next to the 30 amp socket.
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On 20/09/2011 08:57, Matty F wrote:

Yup, extra socket would be fine by the sounds of it. I would not bother with running an extra circuit for it though. i.e. I would have both sockets on the same circuit.
--
Cheers,

John.

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Yes, using the same switch. The switch is on the wall above the cooktop. Cooks will assume that the switch operates on both the cooktop and the oven, as it used to do. A new problem is that the oven has a clock that needs to be reset every time the power is turned off otherwise the oven won't go at all.
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On 20/09/2011 11:19, Matty F wrote:

Is there any reason to actually turn it off? (the switch is really only there for emergencies).
(in the UK it would also be suitable for isolation of the equipment prior to servicing, but I note from your wiring code doc, the switch only needs to be single pole - and so it not adequate for complete isolation)
--
Cheers,

John.

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Perhaps you could obtain from your work a knife switch, a slate board for dual pole fusing, and a wooden connector block.
NT
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