Calculate the required cubic inch capacity for junction boxes, switch boxes, and device boxes per NEC 314. Add conductor rows by AWG size and count, enter the number of devices, grounds, and cable clamps, then compare the total required volume against your box's listed. Part (A), “Box Volume Calculations,” defines the volume of a wiring enclosure or box. The calculations must take into account the volume of the box as well as the volume of any extensions such as domed covers or extension rings. Review fill usage and spare capacity. Electrical Tips and Be Sure to Subscribe! Part (1) of Section 370-16 (a) describes in detail the method of counting wires, as well as clamps, fittings, or devices. To correctly calculate box fill for an electrical box containing multiple switches, you must follow the provisions of National Electrical Code (NEC) Section 314.
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