The short answer
A microwave that trips a breaker, smells hot, arcs inside the cavity or sparks at the plug should be unplugged and left unused. This is the appliance where the gap between a small fault and a serious one is narrowest. Appliances at this end of the market are generously made and electronically supervised, which means the cheap causes present exactly like the expensive ones. Owner work on this appliance ends at the outer case, and that limit is absolute rather than cautious.
What the appliance is doing
- Arcing or sparking inside the cavity — Damage to the wall covering, metal in the cavity, or food residue burning.
- The breaker trips when the appliance starts heating — A fault on the high-voltage side drawing far more than it should.
- A burning smell or visible smoke — Stop at once and unplug: this is not a fault to reproduce.
- NEAR MISS: a smell from food residue burning onto the cavity wall — Unpleasant and not electrical, though it can cause arcing if it is left.
Ranked causes
- Damage or residue inside the cavity — First, and first for a reason. It leads on an appliance of this class because a built-in unit is used heavily and its cavity finish takes the wear that shows up later as arcing. A chipped wall covering, burnt-on food or metal left inside produces arcing. The most common cause of sparks and one an owner can at least recognise.
- Loose or overheated supply connection — Second. A microwave draws hard while heating, and a connection that has loosened makes heat every time it does.
- High-voltage component breaking down — Third. Draws heavily and trips protection, usually at the moment heating begins. Entirely a technician matter.
- Door damage affecting containment — Fourth. A bent door, a damaged seal face or a cracked window is a reason to stop using the appliance regardless of whether it still works.
- Body: The order below is what makes this page worth reading. It is a ranking rather than a measurement, and it carries no numbers because no fact bundle supports any.
The order of checks
- Unplug the appliance and stop using it — Every remaining step is done on an appliance with no power to it.
- Look inside the cavity for burn marks, chipped coating or metal — Arcing leaves visible evidence at the place it happened.
- Look at the plug and socket for heat damage — Scorching points at the connection rather than at the appliance.
- Body: The order below is done with the appliance unplugged and it never involves the cabinet. There is no owner-side electrical test on a microwave.
The checks you can do yourself
- Unplug the appliance and leave it unused — Do not run it again to see whether the symptom repeats.
- Clean burnt residue from the cavity once it is cold — Residue burns and then arcs, so cleaning is genuine prevention.
Tools: cloth
- Photograph any scorching at the plug or in the cavity — It is the evidence a technician needs and it saves time.
Tools: torch
- STOP. Never remove the cabinet or test anything inside — The capacitor can hold a lethal charge after the appliance has been unplugged.
Before you touch it
Safety
Unplug the appliance and never remove its outer cabinet: a microwave contains a high-voltage capacitor that can hold a lethal charge after the power is off, and there is no owner-serviceable part inside. Never defeat a door interlock, never use an appliance with a damaged door or a chipped cavity wall, and never run a microwave empty.
When to call a technician
Every symptom on this page is a service call or a replacement decision, and the appliance should stay unplugged until it is made. Note what you saw and where, because arcing in a specific place, a trip at a specific moment and scorching at a plug each point somewhere different. Note what you saw and where you saw it; arcing in one place points somewhere specific.
Related brands and appliances
The limits of this page
This page is written for the appliance class rather than for one Breville family or model line. Where a family- or model-specific page exists for your unit it is the more specific answer and should be preferred over this one; the brand and appliance hub linked below routes to everything more specific that exists today.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
