How many 12/2 AWG with ground NM cables are allowed in an 18 cubic inch outlet box with a duplex receptacle?

To determine how many 12/2 AWG NM cables can fit in an 18 cubic inch outlet box with a duplex receptacle, it is essential to consider the volume allowances required for the conductors and the box fill calculations in accordance with the National Electrical Code (NEC).

A 12/2 NM cable consists of two 12 AWG conductors and a ground wire. When calculating box fill, each conductor, including the ground, has an associated volume requirement. For 12 AWG wires, each conductor counts as 2 cubic inches. Since each NM cable has two conductors and one ground, you count it as three conductors in total for box fill calculations.

Here’s the breakdown for the fill calculation:

• Each NM cable containing 3 conductors (2 hot, 1 ground) counts as 3 x 2 cubic inches for box fill, which totals 6 cubic inches per cable.

• In an 18 cubic inch box, if you divide 18 by 6, you find that a maximum of 3 NM cables can fit in the box based on the volume requirement.

However, the presence of a duplex receptacle also requires additional volume. Typically, a standard duplex receptacle counts for an additional