oven/cooktop on same branch circuit?

[jevard]

Newbie question... I have an existing electric range (4 burners and oven not sure of power ratings) that I am replacing with separate cooktop (4 burners 30.8 Amps at 240V) and wall oven (20 Amps at 240V). Can I use the existing branch circuit to power both of these? Thanks in advance.

[junkcollector]

How big is the line going to the existing range?

[jevard]

Not sure. I'll look tonight. How big would it need to be for the new oven/cooktop?

[junkcollector]

A rough guess? about 60 amps. Depending on wire insulation, 4 awg. I'd use two seperate circuits.

[junkcollector]

One more thing, How many wires do the new appliances need? 3 wire or 4 wire? 3 wire- 2 hots 1 ground, four wire- 2 hots, neutral, and ground.

If this is an old installation, you may only have three wires (2 hots and neutral) If the new appliances need 4 wires, you will have to upgrade the line anyway.

Check the appliance installation instructions.:top:

[jevard]

I'm planning on running new wiring anyway. The kitchen is being relocated into a different end of the house. So, I guess all I need to know is what size circuit I need to put the oven and cooktop on, is the existing circuit big enough to handle the load, and can both appliances be on the same circuit? By the way, thanks for your responses.

[suemarkp]

No, you don't need that huge of a circuit. A separate cooktop and oven is handled just like a range in the NEC. The absolute worst cast would be a circuit sized per the sum of the loads (51 amps), as neither is a continuous load. But the demand factors allowed for a range still apply to a separate cooktop and oven.

We need to know the KW ratings of the cooktop and oven, and the size circuit you have now, and preferable the gauge and type and number of wires in that circuit (e.g. #8, #6, copper or aluminum, NM or SE cable, 2 or 3 wires plus ground or no ground). We can convert amps to kilowatts if you can verify you have 240V service and not 208V. A 40A circuit may even be sufficient.

If you can run a new circuit to the cooktop, there are some advantages to that (and just use the existing wires for the oven with a smaller breaker). But if not, the two can share the existing larger circuit if you follow some certain rules and it turns out the circuit is large enough.

[junkcollector]

Mark, thank you for catching my mistake.

Let's see, if the applied voltage is 240 and we don't know the VA ratings:

30.4 A X 240 V = 7,392 VA

20 A X 240 V = 4,800 VA

VA total 12,192 VA

2 appliances using Column B of Table 220.55 is 65%

12,192 VA X .65 = 7,925 VA derated / 240 V = 33 A

Sound better?

[suemarkp]

Yes. And if he has a 50A circuit, here's the rules for tapping smaller conductors off of that for a oven and cooktop: 210.19(A)(3)

Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be suffıcient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch circuit conductors. The taps shall not be longer than necessary for servicing the appliance.
Exception No. 2: The neutral conductor of a 3-wire branch circuit supplying a household electric range, a wall-mounted oven, or a counter-mounted cooking unit shall be permitted to be smaller than the ungrounded conductors where the maximum demand of a range of 8 3⁄4 kW or more rating has been calculated according to Column C of Table 220.55, but such conductor shall have an ampacity of not less than 70 percent of the branch-circuit rating and shall not be smaller than 10 AWG.

If he has a 40A circuit, I'm not sure what to do -- probably best to just use #8 splits so they aren't really taps.