A.Harlan Madsen of South Side Electric, an electrical contractor in Bloomington, Minn., responds: A single 14/2 NM feed with three conductors (hot, neutral, and ground) would require a box with a 6-cubic-inch capacity (2 cubic inches for each conductor), while a 3 1/2-inch pancake box has only a 3.9-cubic-inch volume allowance (2008 NEC 314.16).

A 4-inch-diameter pancake box has a 6-cubic-inch volume allowance, enough for a single light fixture but not enough if you’re using a 12/2 feed or making a splice — and not enough if the fixture has a mounting device that occupies space in the box. The NEC does allow the canopy of the fixture to add to the cubic inch capacity of the box, but the...

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