NEC 2026 — 314.16(A) Box Volumes / 314.16(B) Conductor Fill
NEC 314.16(B)(1)
Add each conductor's size, role, and quantity. Conductors that terminate/splice in the box or pass straight through each count once; conductors wholly inside the box (a pigtail that never leaves it) don't count toward fill — a common manual-calc mistake.
NEC 314.16(B)(5)
Any Equipment Grounding Conductors in This Box?
All grounding conductors together count as a single volume allowance, sized to the largest one present — no matter how many grounds are in the box.
NEC 314.16(B)(4)
Add each device strap/yoke and the largest conductor size it connects to. Each device counts as 2 volume allowances.
NEC 314.16(B)(2) / (B)(3)
Internal Cable Clamp(s) Present?
One or more internal clamps together count as a single allowance, sized to the largest conductor in the box.
Luminaire Stud(s) / Hickey(s) Present?
One or more support fittings together count as a single allowance, sized to the largest conductor in the box.
NEC 314.16(A)
Box Fill Results
Required Volume vs. Selected Box Capacity
Add conductors, devices, grounds, clamps, or fittings to calculate required box volume.
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