Box fill check
Volume a box needs for its conductors, devices, clamps and grounds under NEC 314.16, against the box you plan to set.
Expert check pending. This tool shows its formula, cited sources and assumptions with every result, and it's included in its role plan. A qualified expert in this trade hasn't signed the method off yet, so check the result against your own code, engineer or supplier before you rely on it.
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Comes with the electrician plan: every tool for the role, from $10.20 a month at the launch price.
- Your own numbers, worked out as often as you like
- The full box sheet you can print or save to My work
- 3 cited sources, linked, with the checks to make
- Every other tool for the same role, in the same plan
- A plain-words read of your result (a fuller AI read with the Bifrost AI add-on)
Included in these role plans
Example result · fictional numbers
What you get: box sheet
Worked out by this tool from its default inputs. Its role plan lets you run your own numbers, print the sheet and save it.
18.00 cu in needed in 18.0 cu in: 100% full, 0.00 cu in spare
- Box volume
- 18.0 cu in (Table 314.16(A))
- Conductors
- 9.00 cu in (4 insulated conductors)
- Clamps, fittings, devices and grounds (at 12 AWG, 2.25 cu in each)
- 9.00 cu in
- Volume required
- 18.00 cu in
- Box fill
- 100% of the box (OK)
- Spare volume
- 0.00 cu in
Volume count, line by line (NEC 314.16(B))
- 14 AWG conductors
- None (0 cu in at 14 AWG)
- 12 AWG conductors
- 4 × 2.25 = 9.00 cu in
- 10 AWG conductors
- None (0 cu in at 10 AWG)
- Unbroken loops counted twice
- None
- Internal cable clamps
- 1 at 12 AWG, 2.25 cu in
- Fixture studs and hickeys
- None
and 4 more lines
Also on the sheet
- The box, the ring and the order · 7 lines, starting with “Box”
The plain-words read of this example
This box needs 18.00 cu in for its conductors, 1 device, clamps and grounds under NEC 314.16. The 18.0 cu in available is 100% used, so it passes with 0.00 cu in to spare. The allowances use the largest conductor in the box, 12 AWG, which errs on the safe side. For 12 boxes like this, the order is about $42.00.
3 cited sources
- NFPA 70, National Electrical Code (NEC) (National Fire Protection Association)
- NEC free access (read-only, free account) (National Fire Protection Association)
- OSHA 29 CFR 1910.305, Wiring methods, components and equipment for general use (U.S. Occupational Safety and Health Administration)
Plus 5 step-by-step checks, a print layout and a link that reopens it with your numbers.
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