NEC Wire Sizing
What Size Wire for a Built-In Microwave?
The breaker, copper and aluminum wire, and ground for a typical built-in microwave circuit, with the NEC basis and the nameplate caveats that actually decide it.
Built-In Microwave Circuit Spec
| Voltage | 120V |
| Breaker | 20A GFCI |
| Copper wire | #12 |
| Aluminum wire (75°C-marked terminations, SER or conduit) | #10 |
| Equipment ground (Cu) | #12 |
A built-in or over-the-range microwave should have its own dedicated 120V 20A circuit (sized to the nameplate per the manufacturer's instructions). Under the 2023 NEC, a microwave receptacle in the kitchen requires GFCI protection (210.8(A)), the same rule that covers the refrigerator. A countertop unit may share a small-appliance branch circuit, but a dedicated circuit avoids nuisance trips. Wire sized at NEC Table 310.16 (copper lead at the 60°C column for NM-B); ground per NEC Table 250.122. The appliance nameplate lists the exact minimum circuit and maximum breaker; it always governs over a typical value.
Aluminum branch conductors are 75°C-rated AA-8000 alloy (SER cable, or XHHW-2 / THWN-2 in conduit); there is no 60°C aluminum NM-B, so the aluminum row uses the 75°C column. Where the terminations are rated 60°C only, size aluminum from the 60°C column instead (#10 here).
Adding this as a new load? Check whether your panel can handle it (the NEC 220.87 service check), or compare it against the breaker size by load chart.
Size Your Exact Circuit
It opens on this page's 20 A circuit at the 60°C column. For a nameplate that differs from the typical value, enter your exact load and conditions. For a long run, the result links to the voltage drop calculator, which checks that wire over your run; this tool does not size for voltage drop.
Frequently Asked Questions
What size wire do I need for a built-in microwave?
A built-in microwave typically uses a 20A / 120V circuit, which calls for #12 copper (or #10 aluminum) conductors and a #12 copper equipment ground per NEC Table 250.122. A built-in or over-the-range microwave should have its own dedicated 120V 20A circuit (sized to the nameplate per the manufacturer's instructions). Under the 2023 NEC, a microwave receptacle in the kitchen requires GFCI protection (210.8(A)), the same rule that covers the refrigerator. A countertop unit may share a small-appliance branch circuit, but a dedicated circuit avoids nuisance trips.
What size breaker for a built-in microwave?
A 20A single-pole (120V) breaker. The #12 copper conductors are matched to that 20A rating, and it must be a GFCI breaker (or GFCI protection ahead of the appliance). Do not oversize the breaker to a wire it does not protect: the breaker and the conductor go up together. Always confirm against the appliance nameplate, which lists the exact minimum circuit and maximum overcurrent device.
Does a built-in microwave need GFCI protection?
Yes. Current NEC requires GFCI protection for this appliance (NEC 210.8(A), 210.23(B)). Use a GFCI breaker or a GFCI device ahead of it.
Can I use aluminum wire for a built-in microwave?
Yes. On the 75C column (the usual basis for aluminum), a 20A circuit needs #10 aluminum, versus #12 copper. Aluminum is common on larger circuits and services to save cost; apply antioxidant to the terminations, torque to the listed spec, and remember aluminum drops slightly more voltage on long runs.
What size breaker for a microwave?
Same answer: microwave is another name for a built-in microwave. It uses a 20A / 120V circuit with #12 copper wire and a #12 copper ground, GFCI protected. A built-in or over-the-range microwave should have its own dedicated 120V 20A circuit (sized to the nameplate per the manufacturer's instructions). Under the 2023 NEC, a microwave receptacle in the kitchen requires GFCI protection (210.8(A)), the same rule that covers the refrigerator. A countertop unit may share a small-appliance branch circuit, but a dedicated circuit avoids nuisance trips.
Wire Size for Other Appliances
Electric Dryer
#10 copper on a 30A / 240V circuit.
Electric Range
#6 copper on a 50A / 240V circuit.
Electric Wall Oven
#8 copper on a 40A / 240V circuit.
Electric Cooktop
#8 copper on a 40A / 240V circuit.
Electric Water Heater
#10 copper on a 30A / 240V circuit.
Hot Tub
#6 copper on a 50A / 240V circuit.
Dishwasher
#12 copper on a 20A / 120V circuit.
Garbage Disposal
#14 copper on a 15A / 120V circuit.
Refrigerator
#12 copper on a 20A / 120V circuit.
Freezer
#12 copper on a 20A / 120V circuit.
Garage Door Opener
#12 copper on a 20A / 120V circuit.
Wire Size Calculator
Full NEC 310.16 sizing for any load, distance, and conditions.