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 |
| Copper wire | #12 |
| Aluminum wire | #10 |
| Equipment ground (Cu) | #12 |
A built-in or over-the-range microwave should have its own dedicated 120V 20A circuit. 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.
Long Run? Size It Exactly
For a long run where voltage drop matters, or a nameplate that differs from the typical value, enter your exact load, distance, and conditions.
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. A countertop unit may share a small-appliance branch circuit, but a dedicated circuit avoids nuisance trips.
What breaker size for a built-in microwave?
A 20A single-pole breaker. The #12 copper conductors are matched to that 20A rating. Always confirm against the appliance nameplate, which lists the exact minimum circuit and maximum breaker.
Can I use aluminum wire for a built-in microwave?
Yes. For the 20A circuit, aluminum needs #10 (versus #12 copper) at the 75C column. 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.
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.
Wire Size Calculator
Full NEC 310.16 sizing for any load, distance, and conditions.