Check if a home circuit is overloaded by its connected devices.
A branch circuit's capacity in watts is simply its breaker rating multiplied by its voltage — a 20 A, 120 V circuit can carry 2,400 W. What you are allowed to put on it is less than that, because a load running three hours or more at a stretch counts as continuous and is limited to 80% of the breaker rating, which is 1,920 W on that same circuit. Dividing the connected wattage by the voltage gives the current the wiring actually sees. The 80% figure is not a safety-margin superstition: breakers are thermal devices calibrated to trip near their rating over time, and a circuit held at 100% for hours runs the conductors and terminations hot enough to accelerate insulation ageing.
Circuit Load
Breaker capacity = amps x volts; permitted capacity = capacity x 0.8 for continuous loads; utilisation = connected watts / permitted capacity x 100; current = watts / volts
Planning guidance only. Electrical work is governed by the NEC or your local wiring regulations and mistakes cause fires and electrocution — have circuit changes designed and installed by a licensed electrician.
1,800 W at 120 V on paper, but 1,440 W for anything running three hours or more. That is why a 1,500 W space heater is a nuisance-trip generator on a 15 A circuit.
The other way round — wire gauge determines the largest breaker allowed. 14 AWG copper takes a 15 A breaker and 12 AWG takes 20 A; fitting a bigger breaker to existing wire is a fire risk, not an upgrade.
Usually motor inrush or an accumulated thermal load rather than a fault. A breaker at 90% for an hour is already warm, so a compressor or vacuum starting is enough to finish the trip.