Field guide: installing a subpanel, tool list (edition 4)

Core hand tools

A subpanel install lives or dies on the basics. If you're missing one of these, you're making a second truck trip. Build your kit around the work, not the other way around.

Everything on this list assumes you're pulling a permit and the AHJ will inspect. Skip the hardware store specials. Insulated tools matter when you're working near a live service, and the 1000V rating on the handle isn't decoration.

• Klein or Knipex 9" linesman pliers, insulated
• Diagonal cutters and long-nose, both insulated
• 11-in-1 screwdriver plus a stubby #2 Phillips
• Wire strippers rated for 14 AWG through 2 AWG solid and stranded
• Cable ripper for NM and a sharp utility knife for SER or SE
• Torque screwdriver (inch-pound) and torque wrench (foot-pound for lugs)
• Nut drivers, 1/4" and 5/16" minimum
• Tape measure, Sharpie, pencil, and a real level

Torque tools are not optional

NEC 110.14(D) requires terminations be tightened to the manufacturer's specified torque value. "Gutentight" doesn't cut it anymore. Inspectors in a lot of jurisdictions will ask to see the torque tool on the truck, and some want to watch you hit the lugs.

Keep two in the kit. A click-style inch-pound driver for branch breakers and neutral/ground bars, and a beam or click-style foot-pound wrench for the main lugs on the subpanel feeders. Calibrate annually, and don't loan them out.

Tip from a 30-year commercial hand: write the torque spec on a piece of tape and stick it to the inside of the dead front before you close it up. The next guy in the panel will thank you, and so will the inspector on the re-inspect.

Meters and testers

You need to prove the feeder is dead before you land it, and prove it's hot after you energize. A solenoid tester (Wiggy style) or a quality non-contact plus a true-RMS multimeter covers both ends. Don't rely on a tic tracer alone for lockout verification, NFPA 70E is clear on test-before-touch with a contact instrument.

For a 100A or 125A residential subpanel feed, a clamp meter that reads down to milliamps helps you chase neutral-ground bonding mistakes after energization. If the subpanel is in a detached structure, you'll want it, because 250.32(B) bonding issues show up as objectionable current on the EGC.

• True-RMS multimeter, CAT III 600V minimum
• Solenoid tester for absence-of-voltage checks
• Clamp meter with low-current range
• GFCI/AFCI tester for branch circuits downstream
• Receptacle tester with voltage readout

Cutting, drilling, and mounting

Most subpanels go on a finished wall or a piece of plywood on an unfinished stud bay. Either way, you're drilling, cutting knockouts, and fishing cable. A good hole saw kit and a right-angle drill save hours, especially if you're pulling 4/0 SER through a chase.

Knockout punches earn their keep when the stock KO doesn't match your connector. A Greenlee slug buster set (1/2" through 2") handles 95% of residential and light commercial. For feeders in rigid or IMC, you'll want a hydraulic punch or at least a ratchet driver, because hand-knocking a 2" KO in 14 gauge steel will end your day.

• Hole saw kit, 3/4" through 2-1/2"
• Right-angle drill or stubby impact with hex bits
• Greenlee slug buster KO punch set
• Oscillating multi-tool for drywall cutouts around the panel
• Fish tape, 25 ft steel for short pulls, 50 ft fiberglass for conduit

Bonding, grounding, and the stuff people forget

A subpanel is not a service. The neutral bar must be isolated from the enclosure per 408.40 and 250.24(A)(5), and the equipment grounding conductor lands on a separate bonding bar. If you're installing a panel that ships with a main bonding jumper (green screw or strap), it stays in the bag. This is the number one failure on residential subpanel inspections.

For a detached structure fed by a feeder, 250.32(B)(1) requires an equipment grounding conductor run with the feeder and a grounding electrode system at the separate building. Bring rods, acorn clamps, and a #6 solid copper minimum, or #4 if the GEC is exposed.

If you pull the green screw and the panel still reads continuity between neutral and ground at the can, you've got a factory defect or a crossed conductor. Find it before the inspector does.

Labeling and closeout

NEC 408.4(A) requires every circuit to be legibly identified as to its clear, evident, and specific purpose. "Bedroom" doesn't cut it if there are three bedrooms. A label maker beats a Sharpie for anything that's going to get opened more than once.

408.4(B) also requires the subpanel directory to identify the source of the feeder, so note the main panel and breaker number on the inside of the dead front. Include the date, your license number if the AHJ requires it, and the feeder size and type.

1. Brother or Dymo industrial label maker with heat-shrink cartridges
2. Pre-printed circuit directory or a laminated custom sheet
3. Phase tape: black, red, blue, white, green (and gray for 120/208 if applicable)
4. Arc flash label per 110.16 if the calculated incident energy requires it
5. Panel schedule software or a clean paper template, filled in before you leave

Close the dead front, torque the cover screws, and photograph the inside of the panel with the directory visible. That photo has saved more callbacks than any tool in the bag.