Microwave Sparking or Arcing Inside — Causes
Sparking or arcing inside a microwave is alarming but usually has a simple cause. Some are harmless once you remove the trigger; one (a burnt waveguide cover) needs attention before you keep using it.
1. Metal in the Microwave
The most common cause: something metal inside. Twist ties, foil, a fork, metal-trimmed dishes, or even certain "metallic" glazes on plates arc in a microwave. Remove all metal and metal-trimmed dishware. If the sparking stops, that was it — no damage done.
2. Burnt or Damaged Waveguide Cover
The small rectangular cover (usually mica, on the inside wall or ceiling) protects the opening where microwaves enter. Food splatter builds up on it, burns, and then arcs. Check it for dark burn marks or holes. If it is just dirty, gently clean it; if it is burnt through or charred, replace it — it is a cheap part, but arcing on a damaged cover can worsen. Do not run the microwave with a burnt cover.
3. The Metal Rack
If your microwave came with a metal rack, it must be installed correctly on its supports — a rack touching the walls, or used in a model not designed for one, will arc. Make sure it is seated properly or remove it.
4. When to Stop Using It
If there is no metal inside, the waveguide cover is clean and intact, and it still arcs, internal components (like the stirrer or a failing magnetron) may be involved — stop using it and have it serviced or replace it, especially if you see sparks with a burning smell.
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FAQ
Most often metal inside (foil, a fork, metal-trimmed dishes) or a burnt waveguide cover that has food splatter charred onto it. Remove all metal; check and clean or replace the waveguide cover.
Not until you find the cause. Remove metal and inspect the waveguide cover. If it still sparks with nothing metal inside and a clean, intact cover, stop using it and service or replace it.
Always unplug an appliance and shut off its water supply before servicing. This guide is informational and not a substitute for a qualified technician.