Branch Circuits & WiringQuestion 216 of 521
Per 334.80, the ampacity of Type NM (nonmetallic-sheathed) cable is based on which temperature column of Table 310.16?
a.90°C
b.75°C
c.Any column, at the installer's choice
d.60°C
Explanation
Section 334.80 requires NM cable ampacity to be taken from the 60°C column, even though the conductors themselves are 90°C rated. The 90°C rating may be used only for derating calculations, not as the base ampacity.
Law Reference: 2023 NEC §334.80Practice all 521 questions free — no signup required.
Related questions on this topic
- Per Table 310.16, what is the ampacity of a 12 AWG copper conductor in the 75°C column (before any small-conductor overcurrent limit)?
- Per Table 310.16, what is the ampacity of a 10 AWG copper conductor in the 60°C column?
- Per Table 310.16, what is the ampacity of a 6 AWG copper conductor in the 75°C column?
- For Type NM cable, the 90°C rating of its conductors may be used for what purpose?
- A 12-2 Type NM cable (two 12 AWG conductors plus ground) is used for a general branch circuit. Using the required NM temperature column, what is the ampacity of its 12 AWG conductors?
- Per 334.30, Type NM cable must be secured and supported at intervals not exceeding what distance along the run?
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