How do inspectors evaluate whether a dwelling’s circuits meet the 80% rule for continuous loads?

• A. By simply noting total connected load and ignoring continuous factors.
• B. By reviewing load calculations and continuously rated devices to ensure breakers are not oversized for continuous loads.
• C. By using the largest breaker possible for all circuits.
• D. By placing all continuous loads on a dedicated 20A circuit.

Answer: (B)

The important idea is that when a circuit must carry loads that will run for a long time, the protective device (the breaker) must be sized to prevent overheating. That’s the 80% rule for continuous loads: the continuous portion of a circuit’s load must not exceed 80% of the breaker’s rating. Inspectors verify this by doing a load calculation that separates continuous loads (those expected to run for 3 hours or more) from non-continuous ones and then checking that the continuous portion on each circuit won’t push the breaker beyond 80% of its rating.

In practice, this means the inspector looks at the calculated continuous load and confirms the breaker is not oversized for that continuous portion. Equivalently, the continuous load on a circuit should be no more than 0.8 times the breaker’s rating (or, put another way, the breaker must be at least 125% of the continuous load). They also ensure devices on the circuit are capable of operating continuously (continuously rated devices) so that the circuit can handle prolonged use without overheating.

For example, on a 20-amp circuit, the continuous load should be limited to 16 amps or less. If the calculated continuous load approaches or exceeds 16 amps, adjustments are needed—either redistribute loads or use a circuit with a higher rating or separate circuits.

This approach is why simply noting total connected load or using the largest breaker for all circuits isn’t correct, and why you wouldn’t put all continuous loads on a single 20-amp circuit without verifying the 80% limit.