Field guide: installing a subpanel, final inspection (edition 4)

Before you pull the cover

Final inspection on a subpanel is where sloppy work gets caught. The inspector is looking at torque, bonding, grounding separation, and labeling. If those four are clean, you pass. If any one is off, you are coming back with tools.

Walk the install once before the inspector shows up. Cover off, flashlight in hand, check every lug, every strap, every knockout. Look at it like you are the one failing it.

Bring the manufacturer's instructions with you. NEC 110.3(B) requires listed equipment be installed per those instructions, and inspectors do ask. Torque specs live inside the cover or on a label near the main lugs.

Grounding and bonding, the separation rule

This is the single most common fail on a subpanel. In a separately derived system or a subpanel fed from a main service, the neutral and equipment ground must be isolated. NEC 250.24(A)(5) and 408.40 are the citations the inspector will quote back to you.

Pull the main bonding jumper or bonding screw on the subpanel. The neutral bar must float. The ground bar bonds to the enclosure. If you see a green screw driven into the neutral bar, you have a parallel neutral path and a failed inspection.

• Neutral bar isolated from the can (bonding screw removed or jumper cut)
• Separate equipment grounding bar bonded to the enclosure
• Grounds and neutrals on separate bars, one conductor per terminal unless listed otherwise
• Four-wire feeder from the main: two hots, neutral, and equipment ground

For a detached structure fed by a feeder, NEC 250.32(B) requires the equipment grounding conductor to run with the feeder. The old three-wire feeder rule is gone unless the install predates the 2008 code and nothing has changed.

Ran a subpanel in a detached garage last winter. Passed rough, failed final because the previous electrician had left a bonding screw in the neutral bar from a parts-bin panel. Always pull the screw yourself, do not trust the factory.

Torque, the spec the inspector will check

Inspectors carry torque screwdrivers now. NEC 110.14(D) made calibrated torque mandatory for terminations, and it is being enforced. If your lugs are not torqued to the label value, you fail.

Check every lug on the feeder, the main lugs in the subpanel, the ground bar, the neutral bar, and every branch breaker. Mark each one with a torque seal or paint pen so the inspector can see the work was done. A blue or yellow stripe across the screw head sells the job.

1. Feeder lugs on the supply side of the subpanel
2. Ground bar and neutral bar terminal screws
3. Every branch breaker lug, even the ones you did not land conductors on today
4. Any equipment grounding conductor under a green screw in the can

Working space, clearances, and the cover

NEC 110.26 is non-negotiable. Thirty inches wide, three feet deep, six and a half feet high, clear and dedicated. No shelving above the panel, no storage in front, no water heater in the way.

The dedicated equipment space in 110.26(E) extends from the floor to six feet above the panel or to the structural ceiling, whichever is lower. Nothing foreign passes through that zone. A sprinkler pipe is fine, a condensate line is not.

Confirm the cover fits flat, every knockout is filled or has a proper closure plug, and the deadfront does not catch on any conductors. NEC 312.5(C) requires cables to be secured to the cabinet. Romex connectors tight, no exposed sheathing past the clamp, and no more than 75 percent fill through any single knockout.

Labeling and circuit directory

A legible circuit directory is code, not a courtesy. NEC 408.4(A) requires every circuit to be identified as to its clear, evident, and specific purpose. "Lights" is not specific. "Kitchen, south wall receptacles" is.

The panel also needs a label identifying the source per 408.4(B). On a subpanel, that means a label stating where the feeder originates, such as "Fed from Main Panel, garage wall."

• Typed or neatly printed directory, no pencil
• Source of feeder labeled on or near the panel
• Series-rated equipment marked per NEC 110.22(C) if applicable
• Arc flash warning per 110.16 on the exterior of the cover

Inspector I work with fails any directory written in pencil. His logic, pencil fades and the next sparky has no idea what is what. Print it, tape it, laminate it if you want to show off.

Final walk and common gotchas

Before you call for inspection, do a cold walk. Meter every breaker to confirm correct voltage, verify no double-taps unless the breaker is listed for two conductors, and check that AFCI and GFCI protection is in place where required by NEC 210.12 and 210.8.

Look for the small stuff that kills a final. Open knockouts, a missing filler plate on an unused breaker space (NEC 408.7), a neutral landed on the wrong phase's bar, or a handle tie missing on a multiwire branch circuit per 210.4(B).

If the subpanel feeds a dwelling unit or a specific room, verify the feeder ampacity against the calculated load under Article 220. Inspectors rarely recalculate in the field, but they will if the panel looks undersized for what is landed in it.