What Is the 80% Rule for Breakers?

Short answerThe 80% rule limits how much a standard breaker carries for long stretches. Schneider Electric says a standard breaker can be applied at only 80% of its rating for continuous loads, meaning 3 hours or more under the National Electrical Code. It can run at 100% for shorter periods. By our arithmetic, a 15-amp breaker works out to 12 amps.

What this costs

Our national estimates, not quotes.
Option	Job	Low	High
Replace	Electrical Panel Upgrade	$1,000	$3,150

The math for common home breakers

This is our own arithmetic from Schneider's 80% figure. Schneider's FAQ names its PowerPact and Masterpact frames, so applying it to home breakers is our own reading. Volts assume a standard 120-volt circuit.

15-amp breaker: 12 amps continuous, about 1,440 watts.
20-amp breaker: 16 amps continuous, about 1,920 watts.
30-amp breaker: 24 amps continuous.

What counts as continuous

Schneider says the National Electrical Code treats a load of 3 hours or more as continuous. Our own examples of what runs that long on one circuit: a space heater overnight or a car charger. By the same definition, a microwave running for a few minutes isn't a continuous load, though we'd count it toward the total while it runs.

What this rule doesn't mean

It doesn't mean your breaker trips at 80%. It's a sizing limit for long-running loads, and a breaker can run at its full rating for shorter periods. Schneider also notes that some breakers can be applied at up to 100% continuously, and it lists specific frames with a special suffix.

If you keep hitting the limit

Never swap in a larger breaker to stop trips. CPSC warns that overrated fuses or breakers allow overloading that can lead to fire. We recommend moving long-running loads to another circuit, or having a licensed electrician add a circuit. We recommend an electrician for panel work, and we don't give steps for it.

Breaker Keeps Tripping? Causes and When to Call

Common questions

How many amps can I put on a 15-amp breaker?

For a load running 3 hours or more, 12 amps by the 80% rule. For shorter runs, Schneider says a standard breaker can carry its full rating, but we recommend leaving room.

How do I find out what my appliance draws?

University of Washington's workplace guidance says the manufacturer's manual lists how much amperage it draws. CPSC's older guide points to the watts on the appliance's ratings label.