Sizing a junction box is critical for making sure the junction box functions correctly. In a junction box that’s too small, an electrician may have to bend conductors excessively to fit them fully inside the box, which risks damaging the insulation on the wires. Conductors and other components spaced too closely may also create interference or hazardous conditions.

Article 314 of the National Electrical Code contains most of the key regulations that you’ll need to follow when choosing and installing a junction box. These regulations describe in detail the required junction box size, depending on the number and size of conductors and fittings enclosed within the box.

You’ll need to calculate both box volume and box fill when determining the appropriate size for a power distribution box. What do these concepts mean?

Box volume is the total enclosed volume of the junction box, including any extended space provided by attachments such as domed covers or extension rings.