The short answer
A microwave is the highest-current portable appliance in most kitchens, and a trip is usually the circuit telling you it is being asked for more than it has. A burning smell is different: that is the machine itself, and it means stop. Note when it trips. A trip at the moment the cycle starts points at the circuit or the inrush; a trip partway through a long cycle points at the machine heating up. On a Smeg microwave the cause that ranks first is sharing an overloaded branch circuit.
What you observe
- The breaker trips the moment the cycle starts — An inrush or circuit-loading pattern rather than a machine fault.
- A burning or sharp smell during or after a cycle — The machine itself. Stop using it and unplug it.
- NEAR MISS — the machine runs normally but the food stays cold — That is a heating fault, not an electrical safety fault.
Causes, most likely first on a Smeg microwave
- Sharing an overloaded branch circuit — The machine draws heavily the moment the cycle starts, and a circuit already carrying a kettle, a toaster or a heater gives way at that instant. It ranks first on a Smeg microwave because it is the commonest cause on this platform.
- Extension lead, damaged cord or a worn outlet — A microwave on a light extension lead, or in a tired socket, heats the connection rather than the food, and that is what you can smell. Second on this platform: it is the cause that produces a warm plug and a scorch mark, and it is visible without any tools.
- Arcing in the cavity from a damaged waveguide cover — The small mica panel in the cavity wall absorbs splatter, carbonises and then arcs, giving flashes, a sharp smell and eventually damage behind it. Ranked here because you can see it happening, which makes it the one electrical fault an owner can positively identify.
- Line fuse opened by an interlock monitor trip — A deliberate safety circuit shorts the supply and blows the internal fuse if the interlocks operate out of sequence, leaving a completely dead machine. Last, and the reason to work down the list rather than guess: a machine that went dead the instant the door was opened or closed is this, not a coincidence.
Check in this order, and why
- Note what else was running on the same circuit when it tripped — A trip that only happens alongside a kettle is a circuit answer, not a machine answer.
- Feel the plug and the socket face after a few minutes of running — Warmth at the plug is a connection fault and it is urgent.
- Look for a small light-coloured panel in the cavity wall and check it for burn marks — Burnt or blistered mica is the answer on sight.
What an owner can safely check
- Run the microwave alone with everything else on that circuit switched off — If it runs, the machine is fine and the circuit is loaded.
About 10 min
- Unplug, inspect the plug pins and the socket face for scorching, and plug directly into a wall socket — Never run a microwave on a light-duty extension lead.
Tools: torchAbout 10 min
- STOP HERE if the next step needs a meter on live terminals or a panel off — That is where an owner check ends and a service call begins, whatever the ranking above says.
Before you open anything
Safety
Never open the case of a microwave: the high-voltage capacitor can hold a lethal charge long after the machine is unplugged, and there is nothing inside it that an owner may safely service. Unplug the unit at the first burning smell and leave it unplugged.
When to call a technician
Call, or replace the unit, the moment there is a burning smell, visible arcing or a scorched plug — and unplug it and stop using it while you wait. On a European-controlled machine, ask what the control was reporting when it stopped — it usually records why it aborted, and that shortens the visit.
Nearest pages of this class
What this page does not cover
This page is written for the Smeg microwave as a class, not for one family or model line. Where a family- or model-specific page exists for your unit it is linked above, it is the more specific answer, and it is the one to read first. Deliberately not here: part numbers, wiring colours, panel removal order and torque figures, all of which differ between families under the same nameplate.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
