# What size wire for a cooktop and microwave oven on the same circuit?

For the cook top it states amperage is 39.2 and the amperage on the micro oven combo is 30 on a 240v. The model # for GE cook top PEP9030DTBB and the Cafe oven wall CTC912P2NS1 my location is in California currently have a 10 wire for 240 v

• It's generally inadvisable (or even illegal) to combine high-current appliances like that. What's your reason? Feb 9 at 14:36
• Wire size will be the easy part. You will need a sub panel if you want one cable from the main panel to the stoves. If this is a new circuit/you do not have a circuit already for cooking with high amps, you also need a load calculation for the extra 90 amps. Feb 9 at 14:44
• The cooking appliance/range rules are ...special. NEC220.55 Feb 9 at 15:19
• @FreeMan the Lowes ad implies United States of America. Feb 9 at 16:44
• @isherwood In general yes, but not relevant here. There are special (more permissive) rules in the NEC for stoves/ranges/cooktops. Feb 10 at 0:21

NEC 220.55 The weird and whacky range rules. I'd personally prefer a breaker per device, having seen what won't trip a high-amp breaker...

You may also find more restrictive requirements in the manufacturer's instructions for installing the appliance. Those have the force of code, if extant.

Your cooktop is 9.408 KW (as kVA) and your oven has a nameplate KW of 7.2 (If your cooktop has a KW rating lower than 9.408 in its documentation, you can use that instead of 9.408 in the following, but that's all the information you've given us to work with.)

They are treated as equivalent to a "range" of 16.608KW for Table 220.55 according to Note 6 on table 220.55. I'm interpreting that language to mean they get treated as a single appliance at that point, not 2. That makes a significant difference, and I am not entirely happy with the clarity of the language on that point.

Note 1 on table 220.55 requires increasing the demand in column C (8KW) by 5% for each KW or major fraction over 12, so 13, 14, 15, 16, 17 = 25% or 10KW which is 41.67A (or if treated as 5% applied 5 times, 10.21KW and 42.5A)

42A or 43A breakers are not made, but 45A breakers are. A "range" circuit is required to have a 40A minimum breaker by 210.19(C) if the range is more than 8-3/4KW. 45A is larger than 40A so that's covered. 210.19(C) Exception 1 permits sizing the wiring (Tap conductors) to the 30A oven "sufficient to the load served and no longer than necessary to service the appliance" as the breaker is not more than 50A.

Ignore the listed current rating (amperage), unless there is no alternative. If there is no alternative that you can see, post the model numbers of the appliances for more help.

And now with model numbers:

• Cooktop PEP9030DTBB - according to GE specs on web site: Recommended Circuit Breaker (Amps) at 240V = 40A
• Oven CTC912P2NS1 - according to Cafe specs on web site: Amp Rating at 240V = 30A

which means for the cooktop - 8 AWG and for the oven 10 AWG.

Most major appliances from reputable brands will include specific information regarding circuit breaker size. Sometimes they will include a minimum and a maximum, in which case it is your choice. But if there is a minimum and a maximum then I recommend the maximum unless you already have wire capable for the minimum (but not for the maximum) in place and running new wire is a major hassle/expense.

Then size the wire to match the circuit. Check an ampacity table for details. Some typical sizes are:

• 30A = 10 AWG copper cable or 10 AWG copper wire or 10 AWG aluminum wire
• 40A = 8 AWG copper cable or 8 AWG copper wire or 8 AWG aluminum wire
• 50A = 6 AWG copper cable or 8 AWG copper wire or 6 AWG aluminum wire

Most jurisdictions will allow aluminum wire, but you have to make sure that the appliance (if hardwired) or receptacle (if plug/receptacle) is rated for connecting to aluminum. Copper or aluminum wires (as opposed to cables) must be inside conduit.

I highly recommend hardwiring for these types of appliances rather than plug/receptacle. If you use plug/receptacle, make sure they are modern properly grounded receptacles (e.g., NEMA 14 instead of NEMA 10).

Installing separate circuits for each appliance has some big advantages over a shared circuit:

• One circuit can be turned off for servicing a hardwired appliance without affecting the other appliance
• A fault in one appliance tripping the breaker (e.g., for an unknown reason that requires investigation) won't affect the other appliance
• While NEC (see Ecnerwal's answer) allows for combining hardwired cooking appliances within certain constraints, separate circuits guarantees you won't have a Thanksgiving Day disaster due to everything on at once cooking for hours tripping the shared breaker.