The short answer
When a Black+Decker microwave does this, arcing is caused by something conductive in the cavity far more often than by anything inside the case. The load, the cover and the cavity walls are all owner checks with the oven unplugged; scorching is where it stops.
What you actually see
- The oven trips the breaker or the outlet protection — A trip is the protection working and it ends owner diagnosis.
- The plug or the cord is warm to the touch — A warm plug is a poor connection making heat, and it gets worse.
- The oven runs with the door open — A machine that ignores its door is the most serious finding on this page.
- A crackling sound with no food inside — Arcing without a load is a cavity or waveguide problem rather than a food problem.
Causes, ranked for this microwave
- Waveguide cover damaged or dirty — Leads the ranking — it is the second most common cause and the most common one that leaves a visible mark. Where this checks out clean, treat the next entry as the working theory rather than a possibility.
- Food residue burnt onto the cavity wall — Close behind — carbonised food conducts, and a burnt-on patch becomes an arc point that grows every time the oven is used. A clean result here does not just remove one part; it removes everything that depends on it.
- Metal in the cavity — A step down — it is first because it explains most sparking, costs nothing to rule out, and leaves no damage if it is caught immediately. It is worth being sure about this one rather than half-sure, since everything after it assumes a verdict.
What to check, in order
- First — the small cover on the cavity wall — Look at the small panel on the cavity side wall. Grease, scorching or a hole in it is the finding.
- Second — the cavity walls and roof — Run the oven with a cup of water and watch through the door for a spark at the same spot.
Checks an owner can do safely
- Step 1. Inspect the cord, plug and socket — With the oven unplugged, run the cord through your hand and check the pins and the socket for heat discolouration.
Tools: noneAbout 10 min
- Step 2. Give the oven its own circuit — Move it to a socket with nothing else on the run, then note whether the tripping stops.
Tools: noneAbout 15 min
- Step 3. Check what was inside — Look at the dish, the packaging, any trim on the crockery and anything metal that may have gone in with the food.
Tools: noneAbout 5 min
Before you open anything
Safety
Unplug the oven before anything else. A microwave stores enough energy in its high-voltage capacitor to be dangerous with the cord in your hand. Do not remove the cabinet, do not hold a door switch closed, and do not run the oven with the door damaged or ajar.
When this becomes a service call
Stop and call when the next thing to do meets any of these. Stop using the oven and have it replaced or professionally checked if it sparks with a clean empty cavity, trips on its own circuit, or runs with the door open.
Sources
General guidance- The Control of Hazardous Energy (Lockout/Tagout) — OSHA 1910.147 and manufacturer service manuals, fetched
- Article 210 — Branch Circuits — NFPA 70 (National Electrical Code), fetched
Nearest pages
What this page does not cover
Read this as generalized information. It is accurate across the Black+Decker microwave range, which is exactly why it stops short of the detail a single family or model deserves. If a family-level or model-level page exists for your unit, that page supersedes this one on wiring, part numbers and error-code meanings; the links under Related pages are where those pages live.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
