Wiring Cooktop and Under Counter Oven
 

I am confused. We had a frestanding electric range in our kitchen and when we cahnged the counter top to granite we switched to a Cooktop and an under counter oven and broiler. The range was on a 240 volt 40 amp circuit breaker with #8 three wire. No ground just red, black and a white neutral. The cooktop I purchased has also four burners and three of them are 1800 watts and one is 1200 for a maximum of 6600 watts. It say it needs a 40 amp circuit breaker The oven is 2000 watts and the broiler is 3000 for a total of 5000 and it says it needs a 30 amp breaker.

They now say I need two 240 wires for the new units instead of one like the range used. There is no way I can run another #8 wire because my downstairs is finished. I did have a 30 amp circuit available but it has #10 wire instead of #8 that I have redirected to the oven cabinet.

So I have a 40 amp #8 wire available and a 30 amp #10 wire available and I need to findout if I can get by with those wires since the pigtails to both the cooktop and Oven/broiler only have #12 wire in them.

Is there someway I can get by with what I have available with some combination of the two?

Ignore me, Inphase knows exactly what he talking about, he is always very accurate.
Jamie

I don't see the problem. You say you need a 40 A circuit for the cooktop, and you have one. You say you need a 30 A circuit for the oven, and you have one. What's the question?

p.s.: a small caveat in the code even allows you to put them both on one circuit if you want to.

Intresting. Enev with an old 3 wire feed, you could use the same wire / circuit for both?
Jamie

Yes, the code allows for an existing ungrounded circuit to supply cooking equipment and clothes dryers, with the frames grounded through the neutral.

I believe the catch here is that the neutral must be insulated, it can't be the un-insulated "ground" wire being used as both the ground and neutral. Since the op said he has red, black and white, that would indicate he has an insulated neutral wire.

Wiring Cooktop and Under Counter Oven
 

The problem is that the 30 amp circuit has #10 wire coming from the breaker instead of the #8 the oven instructions call for. Yet the wires in the pigtail coming from the devise that were provided by the manafactuer are only #12 wire. The 40 amp circuit breaker has #8 wire running from the circuit breaker to the cooktop and it calls for a 40 amp breaker but the oven only calls for a 30 amp. According to the literature that came with the cooktop If all the burners are on at full power it will pull 6600 watts. If both the broiler and oven are on it will pull 5000 watts, 2000 for the oven and 3000 for the broiler.

I wonder why they call for 8 for 30a.

The size of wires a manfacture uses on there appliance internally or on a short cord mean very little. The wire they use may be rated at a higher temp rating and it is normally for a short distance. They are allowed to do this.

Is this a commercial cooktop?
Jamie

Very interesting. What is the caveat in the code that allows them both to be on one circuit?

Wiring Cooktop and Under Counter Oven
 

No his is not a commercial cooktop or oven. It is strictly for residential use.

Code section 210.19(A)(3) and it's exceptions. Which says, and I'm paraphrasing, that more than one cooking appliance can be served from a single branch circuit so long as the conductors provided on the appliance whip are at least rated for 20 A and the supply circuit is at most 50 A.

I would not worry at all about the instructions calling for #8 wire for the 30 A circuit. The code says that #10 is sufficient for 30 A, and that is being conservative. As long as the #10 cable has an insulated neutral, you are good to go.

I'd use the 8 wire for the oven and the 10's for the cooktop and I wouldn't lose any sleep over it.

Wiring Cooktop and Under Counter Oven
 

Since the cooktop will draw 6600 watts when all the burners are on and the oven/broiler only 5000 if both are on, I'm not sure why you say connect the #8 wire to the oven instead of the cooktop. Also the #8 wire is on a 40 amp beaker and the #10 is on a 30 amp which is what the oven/range manufacturer specifies.

Do I need a separate junction box for each unit or can I run both circuits through the same one?

I want to thank you all for helping me out with this problem.

Perhaps the previous post on the wiring was a typo. I agree, you use the #8 wire 40A breaker for the cooktop, and the #10 wire 30A breaker for the oven. By the way, as a rough guide, you are supplying voltage at approximately 220 volts, and at 30A would supply a total of 6600 watts of power. This is approximate only since this is an AC circuit, not DC, but it is close. A 40A circuit could theoretically supply up to 8800 watts, more if your voltage is actually 240, but again this is approximate because you are on AC, not DC current. So the 30A circuit is sufficient for the 5000 watt appliance, and the 40A circuit is sufficient for the 6600 watt appliance, and this is conservative because you will rarely draw full power anyway.

Your setup is identical to the one I have at home, however my appliances required an independent ground (they are both 240V, 3 wire with ground). Since I ran new circuits for the cooktop and the oven, I ran 3 wire with ground, which is different than what you have. I was not aware of the code exception that allows an existing ungrounded 240V circuit to be used for cooking equipment, however in my case since I ran NEW circuits they had to comply with manufacturer requirements for an independent ground, I guess if I had reused an old, ungrounded circuit I could have grounded through the neutral. Live and learn.

You'd need a really big junction box if you ran both circuits together. I'd just splice them in separate boxes.