A microwave is really two different appliances when it comes to wiring. There is the countertop one you can plug in almost anywhere, and there is the over-the-range or built-in one that is a permanent part of the kitchen. They draw similar power, but the rules around them are not the same, so let us take them in turn.
Power and the circuit
Every household microwave runs on ordinary 120 volts. A countertop model is usually somewhere around 600 to 1,200 watts, while an over-the-range unit is bigger, often 1,000 to 1,800 watts, which works out to roughly 10 to 15 amps once you account for the fact that a microwave draws more power than its cooking wattage suggests.
That power level puts a microwave on a 20-amp circuit with 12-gauge copper wire for anything substantial, and a smaller countertop one can sit on a 15-amp circuit. As ever, the unit’s own label is the final word.
Why a built-in microwave needs its own circuit
Here is where the two part ways. An over-the-range or built-in microwave is fixed in place, and the code treats fixed cooking appliances strictly. There is a rule of thumb that a fixed appliance drawing more than half a circuit’s capacity cannot share that circuit with anything else, and a hungry over-the-range microwave easily crosses that line.
So a built-in microwave should be on its own dedicated 20-amp circuit, not sharing with the kitchen counter outlets that already feed the kettle, toaster and blender. Put it on a shared circuit and you will be tripping the breaker every time two things run at once. A dedicated circuit is the right way, and on new work it is what the code calls for.
A countertop microwave is more relaxed. It can live on a kitchen small-appliance circuit, but the same logic applies in miniature: do not run it on the same outlet as another high-draw counter appliance at the same time, and a large countertop unit is happiest with a circuit of its own.
Never use an extension cord
This one is not negotiable. A microwave pulls a lot of current, and an ordinary extension cord is not built to carry that continuously. Run a microwave through one and the cord overheats, which is a real fire risk. A microwave plugs straight into a proper wall outlet, or is hardwired per the maker’s instructions, full stop. You can read more about how much these appliances pull under microwave oven.
Leave the dedicated circuit to an electrician
Plugging in a countertop microwave is your job. Running the dedicated 20-amp circuit a built-in unit needs, and fitting the right outlet, is electrician work, done to code. We handle kitchen circuits in wiring and installations.
Related reading
- What size wire and breaker does a refrigerator need? for another kitchen appliance that wants its own circuit.
- What size wire and breaker does an electric range need? for the kitchen’s heaviest load.
- Wiring and installations for a dedicated microwave circuit done to code.
What size breaker and wire does a microwave need?
A microwave runs on 120 volts. A larger over-the-range unit, drawing roughly 10 to 15 amps, needs a 20-amp circuit with 12-gauge copper wire, while a smaller countertop model can sit on a 15-amp circuit. Check the unit’s own label, since wattage varies between models.
Does a microwave need a dedicated circuit?
An over-the-range or built-in microwave should have its own dedicated 20-amp circuit, because as a fixed appliance drawing a lot of power it cannot safely share a circuit with other kitchen outlets. A countertop microwave is more flexible and can use a kitchen small-appliance circuit, though a large one is happiest on its own.
Why can’t a built-in microwave share a kitchen circuit?
A rule of thumb says a fixed appliance drawing more than half a circuit’s capacity cannot share that circuit, and a hungry over-the-range microwave crosses that line. Sharing with the counter outlets that feed the kettle and toaster means tripping the breaker whenever two things run at once, so it gets a dedicated circuit.
Can I plug a microwave into an extension cord?
No. A microwave draws a lot of current, and an ordinary extension cord is not built to carry that continuously, so it overheats and becomes a fire risk. A microwave must plug straight into a proper wall outlet or be hardwired according to the manufacturer’s instructions.
What is the difference between countertop and over-the-range microwave wiring?
A countertop microwave is usually 600 to 1,200 watts and can plug into a kitchen small-appliance circuit. An over-the-range unit is larger, often 1,000 to 1,800 watts, and being fixed in place it needs its own dedicated 20-amp circuit. The mounting and the higher draw are what change the requirement.
Do I need an electrician to install a microwave circuit?
For a countertop unit, plugging it in is all you do. For an over-the-range or built-in microwave, running the dedicated 20-amp circuit and fitting the correct outlet is electrician work that should be done to code. The circuit, not the appliance, is the part to leave to a professional.
The next step
Fitting an over-the-range microwave and not sure the kitchen has a circuit for it? It usually needs its own. Get a free quote or message us, and we will run a dedicated microwave circuit and outlet to code, so it is not fighting the toaster for power.