Continuous loads and the 125% rule

Formula

Worked example

A feeder supplies 130 A of continuous load and 110 A of noncontinuous load. The overcurrent device is a standard breaker, not listed for 100% operation. Under 215.3, what is the minimum standard rating for the feeder breaker?

1. The continuous load counts at 125%: 130 × 1.25 = 162.50 A.
2. Add the noncontinuous load at 100%: 162.50 + 110 = 272.50 A.
3. The breaker must be rated at least 272.50 A. The next standard rating at or above it in 240.6(A) is 300 A.

Answer: 300 A

Continuous loads, explained

Breakers and terminals heat up when they carry current for hours. A standard breaker is tested to carry only 80% of its rating continuously, so the NEC makes you size for 125% of a continuous load. 125% and 80% are the same rule seen from opposite sides: 1 ÷ 1.25 = 0.80.

Store and office lighting, parking lot lights, water heaters and EV chargers are typical continuous loads. On the exam, a load is continuous when the question says it runs 3 hours or more or calls it continuous. Do not assume it.

Apply the 125% only to the continuous part, then add the noncontinuous part at 100%. Use the result to pick both the overcurrent device (next standard size up) and the conductor (from the termination column of Table 310.16). The 100% exception for assemblies listed for continuous operation applies only when the question says so.

For conductors there is a second check. The conductor ampacity after correction and adjustment must carry the actual load, without the 125%. The two checks are separate: you do not stack the 125% on top of derating. In the 2026 NEC, load calculations in Article 120 no longer add the 125% themselves; the factor is used when you size the conductors and the devices.

How to solve it on the exam

1. Split the load into continuous (3 hours or more) and noncontinuous amperes.
2. Multiply the continuous part by 1.25 and add the noncontinuous part.
3. For the breaker or fuse, pick the next standard rating at or above that number in 240.6(A).
4. For the conductor, pick the size in the termination column (60 °C or 75 °C) of Table 310.16 that carries that number.
5. If there is derating, also check that the derated ampacity carries the actual load (no 125%), and use the larger conductor of the two checks.

Common mistakes

• Applying 125% to the noncontinuous load too.
• Forgetting the 125% when the question says the load runs for 3 hours or more.
• Rounding the device down to the standard size below the calculated value.
• Multiplying the derated ampacity requirement by 125% as well (stacking both checks).
• Loading a 20 A breaker to 20 A of continuous load instead of 16 A.

Exam tips

• Underline the words continuous, 3 hours or more, and store or office lighting. They tell you the 125% applies.
• Remember the shortcut: a breaker may carry 80% of its rating continuously. 15 A → 12 A, 20 A → 16 A, 30 A → 24 A.

Questions people ask

Sources

• TDLR: Electrician examination information
• Kopperfield: NEC 2026 load calculations

About the tables: The exam is open book. These problems cite the 2026 NEC section and table so you practice finding them in your own book. We never print NEC text or tables.