Field guide: installing a subpanel, time estimates (edition 1)

Scope and why time estimates go sideways

A 100A subpanel in a detached garage and a 60A subpanel in a finished basement are not the same job. Before you quote, walk the run, confirm the feeder path, and check the existing service capacity per NEC 220.83 if you are loading up an older panel. Most blown estimates come from surprises behind drywall, not the panel work itself.

These numbers assume a licensed journeyman working solo, standard residential, copper feeders, and no permit delays. Add a helper and you shave roughly 25% off the raw labor, not 50%. Two bodies in a crawlspace do not move twice as fast.

Load calc, permit pull, and inspector scheduling are separate line items. Do not bury them in labor.

Planning and load calculation

Run the load calc before you size anything. NEC 220.82 for dwelling feeders, 220.87 if you have 12 months of demand data. Undersizing the feeder to save a few bucks on wire is the fastest way to eat a callback and a re-inspection.

Budget real time for this. A clean calc on a straightforward house takes 20 to 30 minutes once you have the nameplate data. A mess of additions, a hot tub, an EV charger, and a mini-split? Closer to an hour, and you want it on paper, not in your head.

• Service capacity check and load calc: 30 to 60 min
• Permit application and plan sketch: 30 to 45 min
• Material takeoff and pickup: 60 to 90 min
• Pre-job walkthrough with homeowner: 15 to 30 min

Feeder run, the real time sink

The panel itself is predictable. The feeder is where jobs die. A 40 foot run through an open basement with accessible joists is 1 to 2 hours of pulling and securing. The same 40 feet through a finished ceiling, around HVAC, and up a chase? Plan on a half day minimum, and that is before patching.

Size the conduit or cable per NEC 310.16 ampacity tables and remember the 60C termination rule on most residential gear per 110.14(C). For a 100A subpanel, 1 AWG copper SER or 1/0 aluminum SER is standard. EMT or PVC runs need to hit fill limits in Chapter 9, Table 1.

If the feeder passes through a separate structure, you need a disconnect at the second building per NEC 225.32. Missing that is the most common red tag I see on detached garage subpanels.

• Open basement or attic, 30 to 50 ft: 1.5 to 2.5 hrs
• Finished space with fishing required: 4 to 8 hrs
• Underground to detached structure (trench already dug): 3 to 5 hrs
• Underground including trenching 50 ft: add 4 to 6 hrs or rent a trencher

Panel mounting, termination, and grounding

Mounting the can, landing the feeder, and setting the grounding electrode system is the part that actually feels like electrical work. On a subpanel, the neutral and ground bars must be isolated. The bonding screw comes out. This is NEC 250.24(A)(5) and 408.40 territory, and inspectors check it every time.

At a separate structure, you drive new ground rods and bond to them per NEC 250.32. Same building, extend the existing grounding electrode conductor or use the equipment grounding conductor in the feeder. Do not re-bond the neutral downstream. Ever.

• Mount panel and knockouts: 30 to 45 min
• Terminate feeder, set main or main lug: 30 min
• Ground rods (two, 6 ft apart) and GEC: 45 to 90 min
• Label circuits and directory per 408.4: 15 to 20 min

Circuit moves and branch work

If you are relocating existing circuits from the main panel to the new subpanel, count every circuit. Each move is 15 to 25 minutes if the conductors reach. If they do not reach, you are splicing in a junction box or pulling new wire, and that circuit just became an hour.

AFCI and GFCI requirements follow the circuit, not the panel. NEC 210.8 and 210.12 apply based on the area served. Kitchen small appliance branch circuits stay on 20A, two minimum, per 210.52(B). Do not cheap out on breakers to hit a number on the quote.

Before you pull the cover on the main, photograph the existing directory and every landed conductor. When something goes dark two weeks later, that photo is the difference between a 10 minute phone call and a service call.

Inspection, total time, and buffers

Rough inspection before you close walls, final after devices. Book the inspector when you pull the permit, not the day you finish. In most jurisdictions you lose a full day waiting on a reschedule.

For a straightforward 100A subpanel in the same building with accessible framing, plan 8 to 12 labor hours plus 2 to 3 hours of admin and travel. Detached structure with trenching and a finished-space feeder, 16 to 24 hours is realistic. Quote the high end. Bill the actual.

1. Same-building subpanel, open framing: 8 to 12 hrs
2. Same-building, finished walls: 14 to 20 hrs
3. Detached structure, underground feeder: 18 to 28 hrs
4. Add 10 to 15% buffer for any panel older than 25 years

Edition 1 of this guide. If your numbers run different in your market, they probably should. Track your own times on three jobs and you will know more than any table.