What you need to know before you start
Replacing a built-in microwave is a job you can do yourself if you are comfortable working with basic tools and electrical connections, but it requires care at several points. The microwave sits in a cabinet opening and connects to power through either a hardwired circuit or a plug behind the unit. You will need to disconnect the old one, remove it from the cabinet, install the new one in the same space, and reconnect the power. The whole job usually takes two to four hours, depending on how tightly the old unit is wedged in and whether you run into unexpected wiring.
The most important safety step is turning off power at the breaker before you touch anything electrical. Built-in microwaves draw significant current, and the circuit should have its own breaker labeled clearly in your panel. If you cannot find it or are unsure about any electrical step, stop and call a licensed electrician—that is not an area where guessing saves money.
Key Takeaways
- Turn off power at the breaker before disconnecting anything, and test that the power is actually off using a non-contact voltage tester.
- Most built-in microwaves are held in by screws on the sides or top of the cabinet frame, not by the trim kit—remove those first.
- The power connection is either a plug you can unplug or hardwired terminals you must disconnect carefully and reconnect to the new unit.
- The new microwave must fit the same cabinet opening; measure the opening width, height, and depth before ordering, because trim kits vary by model.
- If the old unit was hardwired, hire an electrician to connect the new one unless you have experience with electrical terminals and local code.
Measure the cabinet opening and order the right replacement
Before you remove the old microwave, measure the opening where it sits. Measure the width, height, and depth of the empty space—not the microwave itself. Write these numbers down. Built-in microwaves come in standard sizes, but the trim kit (the frame that covers the gap between the microwave and the cabinet) varies by model, and you cannot always swap trim kits between brands.
Check the model number of your current microwave—it is usually on a sticker inside the unit or on the back. Search that number online to find the dimensions and the trim kit part number. When you order a replacement, choose one with the same or slightly smaller external dimensions so it fits in the opening without forcing. If the new microwave is smaller, you may need to order a different trim kit to cover the gap, so confirm that is available before you buy.
Turn off the power and disconnect the old unit
Go to your electrical panel and find the breaker for the microwave circuit. It should be labeled, but if it is not, turn off the breaker that controls the kitchen counter outlets and test the microwave to confirm it is off. Flip the breaker to the off position and leave it off for the entire job.
Use a non-contact voltage tester (a handheld tool that beeps near live wires) to confirm there is no power at the microwave. Touch the tester to the outlet or the power cord connection—if it beeps, the power is still on and you need to find the correct breaker. Do not proceed until the tester shows no voltage.
Open the cabinet doors or remove any trim pieces that are blocking access to the sides of the microwave. Look for screws along the top of the microwave frame or on the sides where it meets the cabinet. These screws hold the unit in place. Remove all of them and set them aside in a small container so you do not lose them.
Disconnect the power connection
Gently pull the microwave toward you to see the back. There will be either a plug connected to an outlet behind the unit, or wires connected to terminal blocks. If there is a plug, unplug it—that is the safest and easiest connection. If the wires are hardwired (connected directly to terminals with no plug), you will see either a wire connector block or individual terminal screws.
For hardwired connections, take a photo of how the wires are connected before you disconnect anything. Usually there are three wires: black (hot), white (neutral), and bare copper or green (ground). Loosen the terminal screws one at a time, remove the wire, and set it aside. Do this carefully so you do not bend the wire ends. If you feel uncertain about this step, stop and call an electrician to handle the disconnection and reconnection.
Once the power is disconnected, slide the old microwave out of the cabinet opening. You may need to tilt it slightly or have someone help you support the weight. Set it aside in a safe place.
Install the new microwave in the opening
Before you slide the new unit in, check that the cabinet opening is clean and free of debris. Look at the back of the new microwave and confirm where the power connection point is located—some models have it on the right side, others on the left or bottom. Make sure you will have access to it once the unit is in place.
Slide the new microwave into the opening carefully, keeping it level as you push it in. It should fit snugly but not so tightly that you have to force it. If it is binding, stop and check that the opening is clear and that you are not tilting the unit. Once it is fully seated, align the trim kit so the gaps are even on all sides.
Reinstall the mounting screws that hold the microwave to the cabinet frame. Use the same screw holes as the old unit. Tighten them firmly but do not over-tighten, as you can crack the plastic frame.
Reconnect the power
If the old unit had a plug, the new one should too. Locate the outlet behind the microwave and plug in the new unit. If there is no outlet or the new unit does not have a plug, you will need to make a hardwired connection.
For a hardwired connection, match the wires from the new microwave to the wires from the old circuit using your photo as a guide. Connect black to black, white to white, and ground to ground. Use wire connectors (the small plastic caps that twist onto joined wires) or the terminal block that came with the new unit. Twist the wires together firmly, then screw the connector on until it is snug. Do not leave any bare wire exposed. If you are not confident doing this, call a licensed electrician—a loose connection can cause a fire.
Once the power is connected, turn the breaker back on at the panel. The microwave should light up and display the time or a setup screen. If nothing happens, turn the breaker off again and check that all connections are tight and correct.
Test the new microwave and reinstall trim pieces
Set the microwave to run for 10 seconds on high power with a cup of water inside. It should heat the water and stop when the timer ends. Listen for any unusual sounds and check that the turntable rotates smoothly. If everything works, turn it off and let it cool.
Reinstall any cabinet doors, trim pieces, or decorative covers you removed at the start. Make sure the trim kit sits flush against the cabinet and the microwave frame, with no gaps. If the new unit is smaller than the old one and the trim kit does not fit properly, you may need to order a different trim kit from the manufacturer or have a carpenter adjust the cabinet opening.
Frequently Asked Questions
Can I install a microwave that is a different size than the old one?
Only if it is smaller and still fits the opening. If the new microwave is larger, it will not fit. If it is smaller, you may need a different trim kit to cover the gap. Measure your opening before you order so you know what sizes will work.
What if the microwave does not turn on after I reconnect the power?
First, check that the breaker is on. Then unplug the unit (or turn off the breaker if it is hardwired) and wait 30 seconds. Plug it back in or turn the breaker back on. If it still does not work, check that all wire connections are tight and correct. If you made a hardwired connection, call an electrician to inspect it.
Do I need a permit to replace a built-in microwave?
Most jurisdictions do not require a permit for replacing an appliance with one of the same type and size. However, if you are adding a new circuit, moving the location, or making significant changes to the electrical setup, a permit may be required. Check with your local building department if you are unsure.
Can I use an extension cord if the outlet is too far away?
No. Built-in microwaves draw too much power for an extension cord, and it creates a fire hazard. If the outlet is not accessible, have an electrician install a new outlet in the right location or hardwire the unit properly.
What should I do with the old microwave?
Take it to an appliance recycling center or a scrap metal facility. Many communities have e-waste collection days. Do not put it in the trash, as it contains materials that should not go to a landfill.