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The #14 Trap That Fails Strong Electricians on Paper
You're at the panel. #14 copper, 75°C terminations.
What's the biggest breaker you can legally land on it?
On the truck, you'd grab a 15 without thinking.
Under the clock on exam day, with Table 2 sitting in front of you, a lot of solid electricians answer 20 — and lose the mark.
Here's why it gets you:
The table says 20. Table 2, #14 copper, 75°C column — ampacity is 20A. That's a real number. If you stop there, you're wrong.
The rule says 15.
Rule 14-104(2) is the small-conductor rule, and it overrides the table for #14, #12, and #10.
No exceptions on a standard branch circuit:
- #14 Cu → 15A max
- #12 Cu → 20A max
- #10 Cu → 30A max
- #12 Al → 15A max
- #10 Al → 25A max
Table 2 even flags this for you — there's a § footnote on those three rows that says "See Rule 14-104(2)." The code is pointing you off the table. Miss that footnote, you fail the question with more information, not less.
The part that catches the people who know code well: Table 13 lets you round up to the next standard breaker size — and the "16-20A" band says 20A is fine. So now two tables in the book are both whispering "20."
The opening line of 14-104(2) — "Except as provided for by Subrule 1)(c)" — is the tie-breaker. That exception is for motors, transformers, heaters, single-luminaire runs under 30-412. A general branch circuit isn't one of them. The hard cap wins. 15A.
The 30-second method, every time you see an ampacity question:
- Cu or Al, and which termination column (4-006)
- Base ampacity off Table 2/4
- #14, #12, #10? Stop. Go to 14-104(2) first. That cap governs, not the table.
- Derating if bundled/hot ambient — Table 5A/5C off the 90°C column, then check against termination rating, take the lowest
- Breaker size: small conductor = the hard cap. Bigger conductor with no exact match = Table 13 next-size-up
This isn't a knowledge gap.
You know this in the field with your eyes closed. It's a paper-navigation gap — and that's the entire difference between "good electrician" and "Red Seal electrician" on exam day.
Drop in the comments: what's the question that's tripped you up under the clock?
I'll break the next one down the same way.
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The #14 Trap That Fails Strong Electricians on Paper
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