A microwave oven transformer is a heavy, cheaply built step-up transformer designed to drive the magnetron in a microwave oven. They typically convert standard mains voltage to around 2,000 volts AC. Hobbyists and bench technicians often salvage them for high-voltage experiments, spot welders, or Tesla coils, though they are notoriously dangerous due to their lethal current capacity.
Heard on the job
Be extremely careful firing up that MOT, because it pushes enough current to kill you instantly.
Insider tip
Unlike neon sign transformers, MOTs are not current-limited. A short circuit will draw massive current until the primary windings melt or the breaker trips.