⚡ Question Of The Week ⚡
Question: A 120V branch circuit supplies a continuous load of 16 amps.
What is the minimum branch-circuit ampere rating permitted by the NEC?
Drop your answer AND NEC reference if you know it ⚡
💬 Comment & discuss below.
⚠️ Disclaimer: Question may be simplified or test interpretation — verify all answers with NEC text.
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Josh A. We got very SHY folks on this forum dude...:)
210.19(A)(1), 210.20(A)... 125%. It's in there several times but these references are specific to branch circuits not over 1000 volts.
Eric Taylor I don't see anything in the question that assumes anything over 1000 volts fella so NEC references you give are very relevant.
Seem 80 percent of 16 would give us the actual load?
Daniel Martens FROM MY UNDERSTANDING: its the other way around for continuous loads.
A branch circuit can only be loaded to 80% of its rating when serving a continuous load (3 hours or more). So instead of taking 80% of 16A, you take the load and size the circuit at 125%.
16A × 125% = 20A
You can then verify it backwards:
20A × 80% = 16A
That's why the minimum branch-circuit rating is 20A per 210.20(A). ⚡
SPOILER: ANSWER KEY BELOW
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2023 NEC (NFPA LINK)
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210.20(A) Overcurrent Protection requires branch circuits supplying continuous loads to be sized at 125% of the continuous load.
Continuous Load = 16A
16A × 125% = 20A
Since 20A is a standard branch-circuit rating per 210.3 and 240.6(A), the circuit must be rated at least 20 amperes.
The Correct Answer would be (B). 20A Branch Circuit. (210.20(A))
💡 Continuous load = a load expected to run for 3 hours or more [Article 100 Definition].