Question 1

How do I calculate box fill?

Accepted Answer

Per NEC 314.16: each conductor counts as 1 of its size; each ground conductor bundle counts as 1 of the largest grounding size; each device yoke counts as 2 of the largest connected size; internal clamps count as 1 of the largest size. Multiply by Table 314.16(B) volume allowances.

Question 2

Do all grounding conductors count individually?

Accepted Answer

No. All grounding conductors in the box together count as a single conductor of the largest grounding size present, per NEC 314.16(B)(5).

Question 3

Does a wirenut count toward box fill?

Accepted Answer

No. Wirenuts and other splicing devices are not included in box fill calculations.

Box Fill Calculator

Box Size

Conductors

Devices & Equipment