The short answer
On an LG microwave, a breaker that will not hold most often comes down to a high-voltage component failing. LG microwaves with inverter power supplies have no heavy transformer, so the classic transformer-and-capacitor reasoning does not apply to them. The first check below is still an owner check, and the list stops where a meter on live terminals begins.
What you observe
- Arcing or sparking inside the cavity — Visible flashes, sometimes with a sharp crack.
- A smell of burning or hot insulation — Something is overheating rather than shorting.
- The breaker trips when the appliance runs — A fault drawing current the moment it is loaded.
- NEAR MISS — the appliance simply does not heat, with no smell or spark — That is a heating fault and a different page.
Causes, most likely first on a LG microwave
- High-voltage component failing — Ranked first here: an inverter supply fails differently and usually more quietly, so a hard breaker trip is a less typical presentation here.
- Damaged or soiled waveguide cover — Ranked second: the small panel in the cavity wall chars when food splashes onto it, and charred material arcs.
- Chipped or rusted cavity paint — Last on this list: bare metal in a chipped cavity arcs and the rust spreads from there.
Check in this order, and why
- Note whether the trip happens instantly or after a delay — Timing distinguishes a short from an overload. First: likeliest cause, least effort.
- Look at the small panel in the cavity wall for scorching — Any charring means stop using the appliance. Second: it separates the next two causes.
- Inspect the cavity floor and walls for chips and rust — Bare metal is the problem, not the appearance. Third: only once the checks above are clean.
What an owner can safely check
- Record what happened and when, then leave it unplugged — Do not reset the breaker repeatedly to test it.
Tools: noneAbout 5 min
- Unplug the appliance and inspect the waveguide cover in good light — Do not run it again once charring is found.
Tools: torchAbout 10 min
- Unplug and inspect the cavity thoroughly, then stop using it if the paint is breached — Do not paint over it with anything not made for the purpose.
Tools: torchAbout 10 min
- STOP HERE if the next step needs a meter on live terminals — That is where an owner check ends and a service call begins.
Before you open anything
Safety
Stop using the appliance and unplug it. Unplug the appliance or switch off its breaker before removing any panel.
When to call a technician
Call now, or replace the appliance. Arcing, a burning smell or a tripped breaker on a microwave means stop: unplug it and leave it unplugged.
Nearest pages of this class
What this page does not cover
This page covers LG microwaves as a class, not one family or model line. It reasons from how LG builds this appliance — enough to rank the causes, not enough for wiring colours, torque figures or part numbers, which differ by family. Where a model-specific page exists it is linked here and is the better answer; this class page has no such child yet, so nothing is withheld by omission.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
