In box-fill calculations, what is the additional volume allowance for one or more fixture studs?

• A. Single Volume Allowance
• B. Double Volume Allowance
• C. Triple Volume Allowance
• D. No Additional Volume

Answer: (A)

In box-fill calculations, you account for anything inside the box that takes up space beyond the wires themselves, including the mounting hardware that holds a fixture. The hardware used to mount a luminaire or device—the yoke or fixture studs—needs a volume allowance, but this allowance is counted as a single unit even if there are multiple studs. So if a fixture uses one or more studs, you add just one additional volume unit to the box-fill total. This keeps the calculation practical: the mounting strap occupies space, but its effect on fill isn’t multiplied by the number of studs. Hence the single volume allowance.