Field guide: installing a subpanel, tool list (edition 2)

Core hand tools

A subpanel install lives or dies by the tools on your belt. Skip the fancy kit. The list below covers 90% of residential and light commercial subpanel work, from knockout to torque-down.

Every tool here earns its weight. If it stays in the truck three jobs running, pull it out of the bag. Subpanel work means tight gear closets, cramped basements, and hot main panels feeding you. You want lean.

• Linesman pliers (9 inch, insulated to 1000V)
• Diagonal cutters and long-nose pliers
• Wire strippers rated for 14 AWG through 6 AWG solid and stranded
• Cable ripper for NM-B, plus a fixed-blade utility knife
• Insulated screwdrivers: #2 Phillips, 1/4 inch slotted, 5/16 inch nut driver
• Torpedo level (magnetic) and a 25 foot tape
• Fish tape or glow rods for feeder pulls
• Non-contact voltage tester and a true-RMS multimeter

Power tools and cutting

Knockouts on a 100A or 125A subpanel can be stubborn, especially on older Square D QO or Cutler-Hammer BR cans. A manual punch is fine for one or two. For anything more, bring powered gear.

Hole saws matter when you are adding conduit bodies or running EMT into a finished can. Bi-metal, sharp, and sized for the connector, not the conduit OD.

1. Cordless hammer drill with 1/4 inch and 3/8 inch masonry bits for lag anchors into block or concrete
2. Knockout punch set (1/2 inch through 1-1/4 inch minimum, hydraulic if you do this weekly)
3. Reciprocating saw with a metal-cutting blade for old cans and BX
4. Step bit (Unibit) for field-drilling blank covers or junction boxes
5. Oscillating multi-tool for trimming drywall around the can flush

Keep a spare Greenlee slug buster die in your pouch. The one you need is always the one that walks off the job.

Testing, torque, and terminations

This is where most failed inspections and callbacks live. NEC 110.14(D) requires terminations to be torqued per the manufacturer's listed value. That means a calibrated torque tool, not a feel for it. Inspectors in more jurisdictions are asking to see the wrench on the bar.

For a typical 100A feeder landing on aluminum lugs, you are looking at 75 to 110 in-lb on the phase conductors and 35 to 45 in-lb on branch breaker terminals. Check the label inside the can. Do not guess.

• Click-type torque screwdriver, 10 to 50 in-lb range
• Torque wrench, 1/4 inch drive, 40 to 200 in-lb, for feeder lugs
• Insulation resistance tester (megger) if the feeder is long or reused
• Receptacle tester with GFCI trip for downstream verification after energizing
• Permanent marker and phase tape (black, red, blue, white, green)

Conduit, connectors, and bonding hardware

Stock the truck for the method you are running. NM-B through a wood-framed interior wall takes clamps and staples. EMT from a detached structure takes benders, straps, and rain-tight connectors. Do not show up with one and need the other.

Grounding and bonding deserves its own mention. A subpanel in a separate building under NEC 250.32 needs its own grounding electrode system, and the neutral and ground must be isolated at the subpanel per NEC 250.24(A)(5). Pull the bonding screw. Always. This is the single most common inspection flag on residential subpanel work.

1. Hand bender sized for your EMT (1/2 inch and 3/4 inch cover most jobs)
2. Anti-oxidant compound (Noalox or equivalent) for aluminum feeder lugs
3. Assorted NM cable connectors, EMT set-screw or compression connectors, and reducing washers
4. Ground bar kit if the can did not ship with one, plus #6 or #4 bare copper for the electrode conductor
5. Listed intersystem bonding termination if the structure does not have one (NEC 250.94)

If you are feeding a detached garage or workshop, carry two ground rods and a rotary hammer with an SDS ground rod driver. Driving rods with a hand sledge in clay soil will ruin your afternoon and your shoulder.

PPE and lockout

Cutting into a live main to land a feeder is category 2 work at minimum. NFPA 70E is not optional, and OSHA will enforce it on any commercial job. Even on residential, your insurance reads the same rules.

Keep a dedicated lockout kit in the truck. One padlock per electrician on site, one hasp, and tags. If you pull the meter instead of killing at the main, call the POCO first or verify your jurisdiction allows it. Some do not.

• Arc-rated shirt and pants, minimum 8 cal/cm2 for typical residential main work
• Class 0 rubber insulating gloves with leather protectors, inspected and in date
• Face shield rated for arc flash, or a full hood for higher category tasks
• Padlocks, hasps, breaker lockout clips, and danger tags
• Voltage tester verified on a known source before and after the test (the three-point check)

The small stuff that saves the trip

Every experienced hand has a parts bin that lives in the truck. For subpanel work, the items below turn a two-trip job into a one-trip job more often than any power tool.

Stock these in a small organizer and restock on Friday. A missing 3/4 inch reducing washer or the wrong neutral pigtail size will send you back to the supply house during rush hour.

• Assorted wire nuts (red, yellow, blue) and push-in connectors rated for the gauges you use
• Green grounding pigtails, 6 inch and 12 inch, pre-stripped
• Spare breakers in the two or three common brands you see locally
• Blank filler plates and twin-breaker handle ties
• A clean rag, a pencil, and a legible panel schedule sticker

Tool lists are personal. Run this for a month, cut what you never touch, add what you reach for twice. The right bag is the one you can carry up a ladder without thinking.