The volume of a box includes the total volume of its assembled parts, including plaster rings, extension rings, and domed covers that are either marked with their volume in cubic inches or are made from boxes listed in Table 314.16(A).

The calculated conductor volume determined by (1) through (5) and Table 314.16(B) are added together to determine the total volume of the conductors, devices, and fittings. Raceway and cable fittings, including locknuts and bushings, are not counted for box fill calculations.

Each conductor that runs through a box and does not have 6 inches of free conductor for splices or terminations in accordance with 300.14, and each conductor that terminates in a box is counted as a single conductor volume in accordance with Table 310.16(B). Conductors that originate and terminate within the box, such as pigtails, aren't counted at all. An Exception notes: Equipment grounding (bonding) conductors, and not more than four 16 AWG and smaller fixture wires, can be omitted from box fill calculations if they enter the box from a domed luminaire or similar canopy, such as a ceiling paddle fan canopy. Caution: Conductor loops occupy space and a box can be excessively filled if we do not take into consideration the increased conductor volume. This can create a serious fire hazard, especially when an electronic device is installed in an outlet box without adequate room for heat dissipation.

One or more internal cable clamps count as a single conductor volume in accordance with Table 310.16(B), based on the largest conductor that enters the box. Cable connectors that have their clamping mechanism outside the box aren't counted.

Each luminaire stud or luminaire hickey counts as a single conductor volume in accordance with Table 310.16(B), based on the largest conductor that enters the box.

Each device yoke (regardless of the ampere rating of the device) counts as two conductor volumes in accordance with Table 310.16(B), based on the largest conductor that terminates on the device.

All equipment grounding (bonding) conductors in a box count as a single conductor volume in accordance with Table 310.16(B), based on the largest equipment grounding (bonding) conductor that enters the box. Equipment grounding (bonding) conductors for isolated ground circuits count as a single conductor volume in accordance with Table 310.16(B).

Splices are only permitted in conduit bodies that are legibly marked, by the manufacturer, with their volume. The maximum number of conductors permitted in a conduit body is limited in accordance with 314.16(B).