Wiring a Garage Woodshop: 120V vs 240V Circuits, Subpanels, and Real Costs

Yo, let me tell you a story.

A guy on my block put a SawStop in his garage and ran it off a 15-amp bedroom circuit with a orange extension cord. He got through two rips before the breaker quit. I told him what I tell everybody: the machines aren't the hard part. The circuit plan is.

So let's work backward from what's actually in the shop.

The Machines Don't Draw What You Think

Start with the nameplates, because that's where the whole plan starts or falls.

The DeWalt DW735 thickness planer is 15 amps at 120V, UL listed. That's from DeWalt's product page, not my memory. You may have heard "12A planer" thrown around — the DeWalt spec sheet says 15A. Use the real number.

The dust collector is where it gets interesting. Grizzly's combined manual for the G0548ZP / G1028Z2 / G1029Z2 / G1029Z2P units lists a 1.5 HP single-phase machine that's 120V/240V, drawing 12A at 120V and 6A at 240V. Same motor, half the current, just reconnected. It also lists 2 HP 240V units drawing 9A. That 12/6 split is the clearest illustration you'll ever get of why 240V matters. It's not that 240V is "more power." It's the same watts. It's half the amps.

The SawStop 1.75 HP Professional Cabinet Saw is a 14A, 120V machine per its product listing. I want to flag this clearly: that listing is a search snippet I couldn't open and confirm directly, and SawStop's own page says reconfiguring to 220V requires an optional kit. I don't know what the 220V amperage is. Neither does this article. Nobody should quote you a number on that without the manufacturer's documentation in hand.

Your Circuit Plan, Roughly

Here's what those three machines actually want.

The planer wants its own 120V circuit, and I would not share it with a shop vac or a space heater. The SawStop wants its own 120V circuit, and I would not run it on the same circuit as the dust collector for the simple reason that you will always run them together. Two separate circuits for the two big 120V tools, one for the dust collector if you're running it at 120V, and you've already got three breakers and three runs before you've hung a single cabinet.

Or: buy the 1.5 HP 120V/240V Grizzly listed in that manual (or reconnect the one you have), and you're at 6A on a 240V circuit. Now the dust collector is no longer fighting the planer for amps.

The reason it's not quite that simple is Article 430, and this is the thing that makes every hobbyist's head spin. Motor circuits don't follow the "breaker protects the wire" rule you learned in Home Depot. Per Field PM's summary of the 2023 NEC:

• Conductors (430.22) are sized at 125% of the table full-load current, not the nameplate.
• The inverse-time breaker (430.52) is sized at 250% of table FLC, and if that doesn't land on a standard size, Exception No. 1 lets you go up exactly one standard size.
• Overload protection (430.32) is what's sized from the nameplate, at 125% for a motor with service factor ≥ 1.15, otherwise 115% — that's from Ampora's NEC 430 guide.

The upshot: it is normal and legal for a motor circuit's breaker to be larger than the wire's ampacity. Field PM cites NEC 240.4(G) as the section that routes motor circuits to Article 430 for exactly that reason. Don't let a code-savvy neighbor tell you your saw circuit is wrong. Know the rule.

Two cautions before you go compute anything. First, both Field PM and Ampora are secondary references, not NFPA text. Second, I could not verify the actual single-phase FLC values from Table 430.248 for 1.75 HP or 1.5 HP motors. So I'm not printing a branch-circuit ampacity for the SawStop or the Grizzly in this article, and you shouldn't either. The method is what you carry to the electrician. They carry the table.

GFCI and AFCI: The Garage Got Stricter

Per WireRef's summary of NEC 2023 §210.8(A)(2), every receptacle in a garage or accessory building needs GFCI — no exception for ceiling outlets or the garage door opener, no height exemption. If the garage is attached to the house, §210.12(A) adds AFCI. WireRef pegs a dual-function AFCI/GFCI breaker at $35–50, which satisfies both, at the panel, in one device.

The 2023 edition also expanded GFCI to 250V single-phase circuits up to 50A where the voltage to ground is 150V or less — which is exactly what a 240V/30A welder circuit on a standard residential panel is.

The practical caveat: WireRef flags older air compressor motors (huge startup inrush) and table saws and planers with universal motors (brush arcing) as the most common sources of nuisance trips on garage GFCIs. Before you commit to a specific machine on a specific GFCI, know that this is a known field problem. Ask your electrician to quote a plan for nuisance trips.

For a detached garage, WireRef states the subpanel feeder itself doesn't need GFCI — protection lives at the receptacle and branch-circuit level. Some sources describe a detached garage needing its own grounding electrode system, typically two rods, but I could not verify the details against NEC text, so treat that as a question for your electrician, not a fact from me.

Every one of these figures comes with WireRef's own disclaimer: derived from NFPA 70 for educational purposes, and your local adopted edition and amendments govern. They mean it. So do I.

Feeder Wire: The Ampacity Table Has a Trapdoor

If you're running a subpanel to the garage, here's the number that matters. From NEC Table 310.16 as reproduced by ElectricalFlux: 6 AWG copper is 55A at 60°C, 65A at 75°C, 75A at 90°C. The 90°C column looks irresistible.

It's a trap. ElectricalFlux points to NEC 110.14(C), the "weakest link" rule — circuit ampacity is limited by the lowest temperature rating of any connected component. NM-B (Romex) conductors are limited to the 60°C column. So a 6/3 NM-B feeder is a 55A conductor no matter what you were hoping. Modern breakers (Square D QO, Eaton BR) are listed for 75°C terminations, which is why 6 AWG THHN in conduit on a 60A breaker gives you a legal 65A. Conduit and individual conductors beat cable here, but only if you're willing to do the pulling.

Derating shrinks it further. From the 90°C column, 4–6 current-carrying conductors in one raceway get an 80% factor, and 40°C ambient gets 0.87. ElectricalFlux's worked example: 75A × 0.80 × 0.87 = 52.2A, which needs a 50A breaker, not 60. Know your ambient and plan accordingly.

What It Costs, Honestly

Now the money. I could only reach one cost source, latestcost.com, a cost-estimating site with no visible methodology and no byline expertise. Treat everything below as planning ranges, not bids.

• 6/3 NM-B copper: $3.00–$7.00/ft, midpoint around $4.75
• 125-ft reel: $375–$875 depending on where in the band
• Electrician labor: $75–$150/hour
• Breaker and termination parts: $40–$250 per circuit
• Permit and inspection: $50–$400 per project
• Installed cable run: $8–$15/ft, up to $20–$30+/ft on difficult routing
• A 75-ft run to a garage appliance: $956–$1,976, which is the closest scenario in the source to what you're actually doing
• Time: 3–6 hours for an accessible run, 6–12 hours if it's involved

Permit fees were only verified for California, and for a 200A main panel upgrade rather than a subpanel. From Electricians Service Team, a licensed California contractor: LA runs $150–$500 (the same page elsewhere says $200–$500 — approximate either way), Orange County $100–$400, San Diego $200–$600, Bay Area $250–$800. Standard residential panel permits, per that page, "typically range from $100 to $500." Which is to say: your jurisdiction will surprise you in both directions.

Here's the California-specific bomb: only a CSLB-licensed contractor can pull a permit for a panel upgrade. Unpermitted work risks fines and denied insurance claims. Whether that licensing rule holds outside California is not something I could verify — ask your electrician.

So do the math on DIY. You save the labor hours. You still pay for the wire, the breakers, the permit, and the inspection. You also take on the torque spec, the derating math, the GFCI/AFCI selection, and the code-compliance risk. If your run is 75 feet, the source's own estimate of $956–$1,976 is not the electrician's fee; that's the whole installed job.

My call: run the plan yourself, price the wire and the breakers yourself, and pay the electrician for the panel work and the termination torque. That's where the code risk concentrates and where the savings from DIY shrink. Half a job calls for half the trade. Nobody in my neighborhood has ever regretted that split.