How to Test and Replace a Microwave Ceramic Fuse

A new chrome microwave oven
  • 1 hours
  • Intermediate
  • 10
What You'll Need
Plastic or rubber gloves
Replacement fuse
Dry cloth

Along with glass fuses, ceramic fuses are among the most commonly used fuses in household electrical appliances. This includes microwave ovens. A microwave oven is prone to short-circuiting caused by severe voltage fluctuations.

The presence of a ceramic fuse ensures that an electrical surge is unable to harm the inner components of the microwave. Unlike glass fuses, those ceramic fuses called "current-limiting fuses" are very fast-acting, filled with sand that melts into glass shall a fault occur, which is an insulator, thus opening the electrical circuit. Sand-filled ceramic fuses also have a higher breaking point since sand can sustain the extra heat to a greater extent. If while protecting the microwave oven a fuse gets blown or melts, it will need to be replaced. This can be easily done by following these steps.

Step 1 - Locate the Ceramic Fuse Holder

Make sure to wear rubber gloves. Ensure the surface around the microwave is completely dry. Remove all the connecting power cords of the microwave. Ideally, you should turn off the main electrically supply. If the room is a bit dark, use a flashlight. Turn the microwave oven so that its rear is accessible. Here, you are likely to find a metallic plate secured with screws.

Some of the older models might have a dedicated fuse box located just below the bottom plate of the microwave. Use a screwdriver to loosen these screws and remove the back-plate. Trace the power cord that will lead you to the main electrical connections. Usually, the microwave fuse holder is located in the vicinity of where the power cord is attached internally.

Step 2 - Locate and Test the Microwave Ceramic Fuse

The fuse holder clips are comprised of mild spring steel and should not be bent. Using a small screwdriver the fuse should be easily snapped out of the holder. If the fuse seems stuck, use pliers for this. Make sure not to induce too much pressure or you might harm the conducting surface of the fuse. You need to test whether the ceramic fuse has blown. To do this, use a voltmeter/ohmmeter. This is necessary for ceramic fuses since they don’t develop a blackened appearance like blown glass fuses.

Use the testing probes of the voltmeter to test the metallic ends of the fuse. The voltmeter suggests the resistance of the fuse. It should give a reading of zero or thereabouts. In blown fuses, the readings are much higher or infinite.

Step 3 - Procure a New Fuse

Some of the fuses may not carry a voltage or amperage labeling. This makes it difficult to decode the appropriate replacement. It is better that you take the blown fuse to an electrical supply store to get an exact replacement. Ideally, you should buy an extra spare fuse.

Step 4 - Replace the Ceramic Fuse

You don’t need tools to install the new fuse. Simply insert it within its dedicated slot in the fuse holder. If the fuse doesn’t seem to fit in its slot, clean the fuse holder and fuse slots. For this, use a dry cloth wrapped around the tip of a flat head screwdriver. Use the covered tip to gently scrape the fuse surfaces. Re-insert the replacement fuse. Secure the microwave back cover and tighten its screws.