The short answer
Sparking inside a Black+Decker EC microwave, a breaker that trips when it starts, or a burning smell are all stop-now conditions rather than diagnostic puzzles. Unplug the oven first and read the rest afterwards. On these models the commonest innocent explanation is metal in the cavity or a worn waveguide cover, and both are checked in a minute with the oven unplugged — but the cabinet is never opened, on any model. What separates EC units here is visible without a tool: a touch panel rather than a dial, or nothing of the sort on the other build.
What you observe on these models
- The breaker trips when the oven starts — Note whether anything else is running on the same circuit.
- Sparks or flashes inside the cavity — Stop it immediately. Metal in the cavity or a damaged waveguide cover are the two usual explanations.
- A hot smell that lingers after it stops — On an over-the-range machine, check whether the filters are loaded with grease.
- The plug or the cord is warm, or the outlet is discoloured — That is the outlet or the connection rather than the oven, and it needs an electrician.
- The circuit visibly struggles with it — A standard household branch circuit is 15 A or 20 A at 120 V, and a microwave asks for a large share of one.
- NEAR MISS — sparks only with a dish with metal trim — Remove the metal; if the arcing goes with it, there is nothing further wrong.
Causes, ranked for the EC build
- Metal in the cavity — foil, trim, a twist tie or a skewer — It ranks first wherever the sparking stops when the offending item comes out.
- The waveguide cover is soiled, burnt or damaged — It ranks high because it is the one internal-looking part that is owner-replaceable from inside the cavity, without opening the cabinet.
- Grease-loaded filters or a blocked vent on an over-the-range machine — It is ranked here because it explains a hot smell with no arcing at all.
- The circuit is shared, or the outlet and cord are damaged — It rises where the oven shares a kitchen circuit with other large appliances.
- A high-voltage component, the magnetron or the diode — It comes last as the diagnosis of exclusion: tripping with nothing in the cavity, clean cover, sound outlet.
Check in this order, and why
- Take the oven out of service before diagnosing anything — Arcing, tripping and burning smells are all conditions to act on rather than to reproduce.
- Check what was in the cavity — Gold and silver decoration on crockery arcs exactly like foil.
- Inspect the waveguide cover on the cavity wall — Char marks or a burnt-through patch explain repeated arcing from one spot.
- Feel the plug and look at the socket — Warmth or discolouration at the wall is an electrician job, not an appliance one.
Before you open anything
Safety
The cabinet stays closed — on every model, for every fault. A microwave oven holds a high-voltage capacitor that can carry a lethal charge after the plug is out, so the only safe work is on the outside: the door surfaces, the turntable, the filters where they are fitted and the outlet it plugs into. Unplug it before touching any of that.
When to call a technician
The condition is whether the cause is in the cavity or behind it. Metal, a charred waveguide cover and greasy filters are all in the cavity or on the outside, and all of them are yours. Anything else — a magnetron, a diode, a capacitor, the wiring behind the panel — is a technician job on an oven that stays unplugged until they arrive.
Other faults covered for the EC models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
