TryBuildCalc

Electrical Box Fill Verification Checklist

Essential Checklist+

Complete these critical checks before approving the work or proceeding to the next construction stage.

✓11 Inspection Points
✓4 Verification Categories
✓Box & Conductor Inputs+
  • Box's actual (or manufacturer-marked) cubic-inch capacity used, not its nominal size
  • Every conductor entering the box and terminating or splicing there is counted
  • Mixed conductor sizes each use their own Table 314.16(B) allowance, not the largest size for all
  • Local code edition and any local amendments confirmed before finalizing
✓Clamp, Fitting & Device Fill+
  • Device/equipment strap count correctly reflects straps, not individual devices
  • Each device/equipment strap group's conductor size reflects what is ACTUALLY connected to it, not the box's overall largest conductor
✓Equipment Grounding Conductor Fill+
  • Total equipment grounding/bonding conductor count confirmed for this specific box
  • 2020+ NEC quarter-allowance rule applied correctly for more than 4 EGCs
✓Installation & Code Compliance+
  • Box confirmed to fit the calculated total fill, or upsized to one that does
  • Permit and inspection requirements confirmed for the scope of the electrical work
  • Box selection reviewed or performed by a licensed electrician
Full QC Checklist+

Verify box/conductor inputs, clamp/fitting/device fill, equipment grounding conductor fill, and installation/code compliance.

✓20 Inspection Points
✓4 Verification Categories
✓Box & Conductor Inputs+
  • Box's actual (or manufacturer-marked) cubic-inch capacity used, not its nominal size
  • Every conductor entering the box and terminating or splicing there is counted
  • Conductors passing through the box without splicing are still counted
  • Mixed conductor sizes each use their own Table 314.16(B) allowance, not the largest size for all
  • Local code edition and any local amendments confirmed before finalizing
✓Clamp, Fitting & Device Fill+
  • Internal clamp fill correctly counted as ONE allowance regardless of clamp count
  • Fixture stud and hickey fill correctly counted per TYPE of fitting, not per instance
  • Device/equipment strap count correctly reflects straps, not individual devices
  • Largest-conductor determination for clamp/fitting fill includes the EGC, not just circuit conductors
  • Each device/equipment strap group's conductor size reflects what is ACTUALLY connected to it, not the box's overall largest conductor
✓Equipment Grounding Conductor Fill+
  • Total equipment grounding/bonding conductor count confirmed for this specific box
  • 2020+ NEC quarter-allowance rule applied correctly for more than 4 EGCs
  • EGC size entered matches the actual largest equipment grounding conductor in the box
  • EGC volume confirmed as ADDED on top of conductor/clamp/fitting fill, not substituted for it
  • Isolated-ground EGCs (per NEC 250.146(D)) included in the same unified EGC count, not omitted
✓Installation & Code Compliance+
  • Box confirmed to fit the calculated total fill, or upsized to one that does
  • Box remains accessible after installation, per NEC 314.29
  • Box fill re-checked after any remodel work that adds conductors, devices, or EGCs to an existing box
  • Permit and inspection requirements confirmed for the scope of the electrical work
  • Box selection reviewed or performed by a licensed electrician
Inspection Notes+
Use the latest approved drawings, specifications, and site measurements.
Complete all critical checks before proceeding to the next work stage.
Record deviations and confirm rectification where required.

Related Calculators & Guides

Electrical Box Fill CalculatorOpen the related calculator and verify the current project inputs.

FAQ

Use it after collecting the project inputs and again before approving or closing the relevant work stage.
No. It supports verification but does not replace approved drawings, specifications, codes, manufacturer requirements, or professional inspection.