The short answer
Electrical symptoms on a microwave divide sharply into things that are a cooking mistake and things that mean stop using the oven. Arcing from metal or a dirty waveguide cover is the first kind; a tripping breaker, a burning smell or a scorched cord is the second, and none of it is investigated with the case off.
What you actually see and hear
- Sparks or arcing inside the cavity while cooking — Metal in the oven, or a damaged waveguide cover. Stop and look.
- The breaker trips when the oven starts — A real electrical fault. Do not keep resetting it.
- A burning or acrid smell with no food to explain it — Stop using the oven. That smell comes from inside the case.
- The oven is warm or discoloured at the plug or cord — A connection problem, and a fire risk rather than an inconvenience.
- NEAR MISS - the kitchen lights dim slightly when it starts — Common on a shared circuit, and not by itself a fault.
Causes, most likely first on this machine
- Metal in the cavity — First, because it is the most common and the least serious: foil, a decorated plate or a twist tie arcs immediately and stops when it is removed.
- A damaged or soiled waveguide cover — Second. Food splash burns onto the cover, and a burnt patch arcs every time the oven runs.
- Shared or overloaded branch circuit — Third. A standard household branch circuit is fifteen or twenty amps, and a microwave sharing one with a kettle or a toaster can trip it without anything being faulty.
- A failing component inside the case — Fourth. It produces burning smells, repeated tripping and sometimes a loud hum - and it is exactly where owner involvement ends.
- Cord, plug or outlet fault — Last, and easy to spot: heat or discolouration at the plug is a connection problem and it is urgent.
Check in this order, and why
- Stop the oven and look inside for metal — One look settles the commonest cause.
- Inspect the waveguide cover for burnt or missing patches — It is the small panel on the cavity wall.
- Find out what else is on the circuit — A shared circuit explains many nuisance trips.
- Look and feel at the plug and outlet — Heat or discolouration here is a stop-now finding.
What an owner can safely check
- Unplug the oven before inspecting anything — Never remove the outer case, whatever the symptom.
About 5 min
- Remove all metal from the cavity and clean the interior — Foil, twist ties and decorated crockery all arc.
Tools: cloth, mild detergentAbout 15 min
- Clean the waveguide cover gently and inspect it — A burnt or damaged cover means stop until it is replaced.
Tools: clothAbout 10 min
- Plug the oven into an outlet with nothing else heavy on it — Separates a shared-circuit trip from an appliance fault.
About 10 min
- Reset the breaker once and watch what happens — If it trips again, stop. A repeat trip is a fault, not a nuisance.
About 5 min
- STOP USING THE OVEN for any burning smell, repeat trip or hot plug — Those symptoms are from inside the case, and the case does not come off.
Before you open anything
Safety
Unplug the microwave before you clean around the door or touch anything on the cabinet. Do not remove the outer case under any circumstances: the high-voltage capacitor inside holds a lethal charge long after the oven is unplugged, and microwave ovens are one of the few domestic appliances that genuinely kill people who open them. Never defeat, tape or prop a door latch, and never run the oven with the door damaged.
When to call a technician
Call an electrician when the breaker trips with the oven on its own circuit, and a technician or the supplier for any burning smell, internal arcing or loud hum. Stop using the oven in the meantime in all three cases. This is the one kitchen appliance where the honest advice is that there is nothing to attempt: the stored charge inside makes it dangerous to open even unplugged, and on a countertop model replacement is usually cheaper than the repair anyway.
Nearest pages of this class
What this page does not cover
This page is written for the domestic microwave oven class, not for one family or model line. Where a brand- or model-specific page exists for your unit it is the more specific answer and it is linked above, so go there first if your machine is named. What is deliberately not here: magnetron and capacitor specifications, fuse ratings, interlock part numbers and cabinet cut-out dimensions, all of which differ by family and belong on the page for that family.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
