Field guide: installing a subpanel, final inspection (edition 5)

Before the inspector shows up

Final inspection on a subpanel is not the time to discover a missing bonding screw or a neutral landed on the ground bar. Walk the install yourself with the same checklist the AHJ will use. If you find it first, it costs you ten minutes. If they find it, it costs you a trip back.

Pull your permit card, approved plans, and load calc. Most inspectors want to see the calc matches what is actually installed, especially if you upsized conductors or added circuits during rough. Have NEC 408.4(A) circuit directory filled out legibly, not with pencil scratch that reads "lights?" on four different lines.

Tip from a 30-year journeyman in Phoenix: keep a spare green bonding screw and a roll of white tape in your inspection bag. Nine times out of ten that is the callback.

Grounding and bonding, the number one fail

This is where most subpanels get red-tagged. In a subpanel fed from the same structure, the neutral and ground must be separated per NEC 250.24(A)(5) and 408.40. The main bonding jumper or bonding screw that came with the panel should be removed or left out. Grounds land on the ground bar, neutrals on the isolated neutral bar.

If the subpanel is in a separate structure, 250.32 applies. As of the 2008 code cycle and later, you run four wires (two hots, neutral, equipment grounding conductor) and keep neutral and ground separated at the subpanel. The old three-wire feeder method is gone for new installs.

• Bonding screw removed or green screw backed out and bagged in the panel
• Equipment grounding conductor sized per 250.122 based on the feeder OCPD
• Ground bar bonded to the enclosure, neutral bar isolated
• All EGCs terminated under individual lugs, one conductor per hole unless listed otherwise

Conductor terminations and torque

Since the 2017 code cycle, NEC 110.14(D) requires terminations be torqued to the manufacturer's specs using a calibrated tool. Inspectors in a growing number of jurisdictions are asking to see the torque screwdriver or wrench and the label sticker inside the panel. Bring both.

Check every lug, including the feeder terminations at the main and the subpanel. Aluminum feeders need anti-oxidant compound where specified by the lug listing. Copper does not, but a dab will not fail you. What will fail you is a loose neutral lug that shows arc tracking when the cover comes off.

1. Torque feeder lugs to the value stamped on the panel or in the instruction sheet
2. Torque each breaker terminal, even the ones you did not install today
3. Retighten after the first thermal cycle if you can, especially on aluminum
4. Mark torqued screws with a paint pen if your AHJ wants visual proof

Working clearances and physical install

NEC 110.26 working space gets overlooked because it was fine at rough. Then the HVAC guy hung a condensate line, the plumber ran a trap primer, or the homeowner stacked totes in front of the panel. Walk the 30 inch wide, 36 inch deep, 6.5 foot tall envelope and clear it.

Verify the panel is mounted plumb, dead front is flat against the tub, and no knockouts are open. Missing KO? NEC 408.7 says close it with a listed closure, not a hunk of duct tape. Check that cables entering the top or sides have proper connectors and the bushings are in place on conduit over 250 volts or where required by 300.4(G).

If the panel sits in a finished space, confirm the cover screws thread cleanly. A stripped screw on a flush-mount cover is a five dollar part and a one hour drive back.

Circuit identification and AFCI/GFCI verification

408.4(A) requires every circuit to be legibly identified at the panel. "Spare" is acceptable for unused breakers. "Kitchen" is not acceptable for a kitchen with three small appliance circuits, a dishwasher, a disposal, and a microwave. Inspectors are increasingly picky about this. Print a typed directory if your handwriting is bad.

Test every AFCI and GFCI breaker with the test button before the inspector arrives. If a breaker will not trip on the button, it is defective, swap it. Verify protection scope matches code: 210.8 for GFCI, 210.12 for AFCI, 210.8(F) for outdoor outlets on dwelling units (2020 and later cycles), and any local amendments your jurisdiction has added.

• Kitchen, bathroom, laundry, garage, outdoor, unfinished basement: GFCI
• Dwelling unit bedrooms, living rooms, kitchens, laundry, and most other 120V 15/20A: AFCI
• Dishwasher: both AFCI and GFCI on current cycles, check your adopted edition
• HVAC disposal outlets: verify the local amendment before guessing

Final walkthrough with the inspector

Meet the inspector at the panel with the cover off, directory filled in, torque tool visible, and permit card signed. Answer direct questions directly. If you did something unusual (parallel feeders, a tap rule under 240.21, a feeder through a detached structure), have the code section cited and ready.

If you get a correction, read it back out loud and confirm the specific article. Vague red tags like "grounding issue" are not useful on the reinspection. Get the inspector to write the NEC reference or describe the exact condition. Fix it, document it, call for reinspection. Clean passes come from clean prep, and clean prep comes from treating your own final walk like the real one.