The maximum number of #10 current carrying conductors in a 1 1/4 inch EMT, for general use is?

• A. 32
• B. 28
• C. 25
• D. 35

Answer: (B)

Conduit fill is the main idea here: how many conductors can physically fit inside a raceway without crowding and overheating. The NEC sets a limit on the total cross-sectional area of all conductors inside a raceway relative to the inner area of the raceway, and for common THHN/THWN insulation this works out to about 40% of the interior space being used by conductors. In a 1 1/4 inch EMT, that limit corresponds to up to 28 No. 10 current-carrying conductors for general-use installations. Ground wires don’t count toward the fill, and neutrals count only if they carry current. If more than three current-carrying conductors are in the raceway, you must derate the ampacity of the conductors, but that derating is separate from how many conductors you’re allowed to physically place in the conduit.