Key takeaways
- Five 3 HP, 230 V saws carry nameplates from 12.8 to 14.5 A. NEC Table 430.248 gives every 3 HP single-phase motor at 230 V the same 17 A, and Article 430 sizes the circuit from that table.
- Conductors must carry 125 percent of the table current, 17 x 1.25 = 21.25 A. 12 AWG NM-B cable is 20 A in the 60 C column and fails. 10 AWG NM-B is 30 A and passes.
- The nameplate reading gives 14.5 x 1.25 = 18.1 A at most, which 12 AWG NM-B would pass. That 3 A gap is the whole disagreement between the two answers.
- An inverse time breaker may be up to 250 percent of 17 A, 42.5 A, rounded to the next standard size of 45 A. The makers ask for 15 or 20 A, the bottom of that band.
- The receptacle caps the breaker in practice. A single receptacle on its own circuit must be rated at least as high as the breaker, so a NEMA 6-15 outlet means a 15 A breaker.
Two answers circulate. One says a 3 HP saw is a 13 A machine, so 12 gauge on a 20 A breaker is plenty. The other says 10 gauge and a 30 A breaker, every time. The first reads the nameplate. The second reads the National Electrical Code, which does not use the nameplate for this job. Below, five 3 HP saws' nameplates and circuit advice sit beside the code arithmetic, and the part nobody mentions, the receptacle, turns out to set the breaker.
Two currents for one motor
The SawStop PCS31230 is listed at "3 HP", "230V" and "13A". SawStop's manual says the same: the motor "is rated at 3 hp" and "draws 13 amps at 208-240V power."
NEC Table 430.248, for single-phase AC motors, gives a different number, as reproduced by Elliott Electric from the 2020 NEC:
| Horsepower | 115 V | 208 V | 230 V |
|---|---|---|---|
| 3 HP | 34.0 A | 18.7 A | 17.0 A |
| 5 HP | 56.0 A | 30.8 A | 28.0 A |
The table's currents "are for system voltage ranges of 110 - 120 and 220 - 240", so a 230 V motor on a 240 V service reads 17 A.
Which number does the circuit get? Mike Holt's guide to the 2020 NEC: under 430.6(A)(1), the table currents "are used to determine conductor sizing [430.22] and the branch-circuit short-circuit and ground-fault overcurrent protection size." The nameplate, "is not permitted to be used to determine the conductor size and the motor short-circuit and ground-fault overcurrent protective device" except for motors that are not on continuous duty. The nameplate's job is the overload device, below.
Five 3 HP saws: what the label and the manual say
Every 3 HP, single-phase saw checked for this page:
| Saw | Nameplate current | At | Circuit the maker asks for | Plug supplied | Table 430.248 current |
|---|---|---|---|---|---|
| SawStop PCS31230 (Professional Cabinet Saw) | 13 A | 208-240 V | none stated; time delay fuse marked D if fused | NEMA 6-15P, 9 ft cord | 17 A |
| Powermatic PM2000B, 3 HP (PM231B) | 14.5 A | 230 V | 20 A, dedicated | none, cord and plug not supplied | 17 A |
| Grizzly G1023RL | 14 A | 240 V | 15 A minimum | NEMA 6-15 | 17 A |
| Grizzly G0690 | 12.8 A | 220 V | 20 A minimum | NEMA 6-20 | 17 A |
| Grizzly G0651 | 13 A | 220 V | 15 A minimum | NEMA 6-15 | 17 A |
The nameplates span 12.8 to 14.5 A, and the table gives all five 17 A, 1.17 to 1.33 times their labels. The makers' advice is 15 or 20 A, a circuit rating, which means the breaker. None of the five manuals names a wire gauge for the building circuit.
Powermatic alone prints a starting current: 86 A for the 3 HP PM2000B, 5.9 times its 14.5 A nameplate, for the instant the motor starts. Its circuit figure also carries a footnote, "subject to local/national electrical codes", and the manual adds, "Local codes take precedence over recommendations." The makers do not claim to override the code.
The wire: 17 x 1.25 = 21.25 A
Section 430.22 sets the conductors. In Holt's words, conductors for a single motor "must have an ampacity of not less than 125% of the motor full-load current rating", with that current taken from the table:
17 A x 1.25 = 21.25 A
Cerrowire's ampacity chart, built on the 2017 NEC with no corrections applied, lists copper in three temperature columns:
| Copper | 60 C (NM-B, UF-B) | 75 C (THW, THWN, XHHW) | 90 C (THHN, THWN-2, XHHW-2) | Passes 21.25 A? |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A | No, in NM-B or at 75 C |
| 12 AWG | 20 A | 25 A | 30 A | No in NM-B; yes at 75 C |
| 10 AWG | 30 A | 35 A | 40 A | Yes in every column |
| 8 AWG | 40 A | 50 A | 55 A | Yes, more than needed |
12 AWG NM-B, the ordinary cable in a house or garage wall, is 20 A, 1.25 A short. 10 AWG NM-B is 30 A and passes. In NM-B, the 10 gauge answer is right.
12 AWG is not ruled out everywhere. In the 75 C column it is 25 A, which clears 21.25 A, and Holt's worked example for a 2 hp motor reads that column: 12 A x 1.25 = 15 A, "14 AWG rated 20A at 75°C." So 12 AWG THWN can pass where that column applies. Cerrowire lists NM-B only under 60 C. (AWG, incidentally, is a different scale from the sheet steel gauge on a tool cabinet, as the steel gauge guide shows.)
Run the arithmetic on the nameplate instead. The highest label above, the PM2000B's 14.5 A, gives 14.5 x 1.25 = 18.1 A, which 12 AWG NM-B would pass. That is the whole disagreement: 18.1 A on the nameplate reading, 21.25 A on the code's, and 12 AWG NM-B's 20 A between them. On a 208 V supply, 18.7 A x 1.25 = 23.4 A: 12 AWG still passes at 75 C and fails in NM-B.
The breaker band, from the maker's floor to the code's ceiling
The ceiling is Table 430.52. For an inverse time breaker, the ordinary panel breaker, the maximum is 250 percent of the table current, as in Holt's 2 hp example, 12A x 2.50 = 30A, with "next size up" under 240.6(A) where the result is not a standard size. For 3 HP:
17 A x 2.50 = 42.5 A, so the next standard size is 45 A, from 240.6(A)'s list of 15, 20, 25, 30, 35, 40, 45, 50, 60 and up.
The floor is the motor's start. Holt adds that the protective device must be "capable of carrying the motor's starting current." No code table gives that number, so the makers' figures set the floor. Grizzly's minimum circuit for its 13 and 14 A saws is 15 A, and Powermatic's recommendation for its 14.5 A saw is 20 A.
| Limit | Arithmetic | Breaker |
|---|---|---|
| Maker's minimum, Grizzly G1023RL and G0651 | as printed | 15 A |
| Maker's recommendation, Powermatic PM2000B and Grizzly G0690 | as printed | 20 A |
| Code maximum, inverse time breaker, 230 V | 17 x 2.50 = 42.5, next size up | 45 A |
| Code maximum at 208 V | 18.7 x 2.50 = 46.75, next size up | 50 A |
| Code maximum if the motor will not start (Exception 2) | 17 x 4.00 = 68, may not be exceeded | 60 A |
| Dual-element time delay fuse instead | 17 x 1.75 = 29.75, next size up | 30 A fuse |
The 400 percent line applies only when the motor will not start on the lower figure, and it rounds down because that limit cannot be exceeded.
Why can the breaker be twice the wire's working current? Because on a motor circuit the breaker does not handle overload. Section 430.32 puts a separate overload device on a continuous duty motor over 1 hp, set to open at no more than 115 percent of the nameplate: 13 x 1.15 = 14.95 A for the SawStop, 14.5 x 1.15 = 16.7 A for the PM2000B. That is where the nameplate is used, and Holt notes that the branch conductors "are protected against overloads by the overload device." Grizzly's G0690 lists a "Magnetic Switch w/Overload Protection", and the PM2000B's parts list includes an overload relay. If a manual does not show where the overload protection is, ask the maker before going above its breaker figure.
The receptacle sets the breaker you can actually use
The outlet narrows the 15 to 45 A band. Section 210.21(B)(1): "A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit." A dedicated saw circuit with one receptacle is that case.
| Saw plug | Receptacle | Largest breaker for a single receptacle |
|---|---|---|
| NEMA 6-15 (SawStop PCS, Grizzly G1023RL and G0651) | 6-15R | 15 A |
| NEMA 6-20 (Grizzly G0690) | 6-20R | 20 A |
| NEMA 6-30, after a plug change | 6-30R | 30 A |
The wire does not change with the breaker: 430.22 is tied to the motor, so even a 15 A circuit needs 21.25 A conductors.
So a 30 A breaker is legal under Article 430 with 10 AWG NM-B, but only with a 30 A receptacle, which on a SawStop means a new plug. Its manual says "No adapter is available or should be used" and to fit a plug that "matches the single phase 208-240V power outlet from which you intend to power the saw." The PM2000B ships with no plug, and its manual allows a UL/CSA listed plug or hard-wiring with a disconnect near the operator.
Which answer is right
The code is right for the wire: 21.25 A, 10 AWG in NM-B, for any 3 HP single-phase saw at 230 V. The makers are right for the breaker floor: 15 or 20 A, well inside the code's band.
The 12 gauge answer persists because it is what the nameplate times 1.25 gives, and because a 20 A recommendation looks like an ordinary 12 AWG, 20 A circuit. Built in 12/2 NM-B, it fails 430.22 by 1.25 A. The 30 A answer is one legal choice among several, and it needs a 30 A receptacle.
One build that meets every rule here, for a 6-20 saw: 10/2 NM-B with ground, a 20 A double-pole breaker and a single 6-20R. Run 10 AWG even when starting at 15 A, so a later saw or plug change moves only the breaker and receptacle. Plan the run before the wall system goes up, as the garage shop layout guide advises for dedicated circuits generally. A compressor is the other motor that wants its own circuit in most shops, and how hard its pump works is set out in whether a bigger compressor tank gives more CFM.
Extension cords at 240 V
SawStop's cord recommendations "for 208-240V wiring" are 14 AWG to 50 ft and 12 AWG from 50 to 100 ft, with over 100 ft "Not Recommended". Powermatic's table, at 240 V for a 12 to 16 A tool, lists 14 AWG to 50 ft, 12 AWG to 100 ft and "Not Recommended" at 200 ft.
That is twice the reach of a 120 V tool: the 120 V tables stop a 15 A saw's 12 gauge cord at 50 ft, as compared across four makers in what gauge extension cord a 15 amp tool needs. Using the copper resistance figures on that page:
| Cord | Saw current | Drop | Share of 230 V |
|---|---|---|---|
| 50 ft, 14 AWG | 13 A (SawStop) | 0.252 ohm x 13 = 3.3 V | 1.4% |
| 100 ft, 12 AWG | 13 A (SawStop) | 0.318 ohm x 13 = 4.1 V | 1.8% |
| 100 ft, 12 AWG | 14.5 A (PM2000B) | 0.318 ohm x 14.5 = 4.6 V | 2.0% |
The resistance counts both conductors, out and back. Each volt lost is also half as large a share of 230 V as of 120 V, which is why the 240 V tables reach further. A long 12/3 cord is a heavy coil, and it belongs on a hook off the floor, the job track wall does best in the wall storage comparison.
The cord is not the branch circuit. Grizzly's G1023RL ships with a 14 AWG cord, but the wall behind the receptacle is sized by 430.22, not by the cord.
On a generator
The charts in the generator guide for a 15 amp table saw cover 120 V saws, and that page lists 240 V cabinet saws as out of scope. The PM2000B's 86 starting amps at 230 V come to 86 x 230 = 19,780 VA at the instant of start, against the 4,500 W those charts print for starting a 15 A saw. That is arithmetic on the manual's figure, not a generator rating, so take it to the generator maker.
Where this answer stops applying
- 5 HP saws. Table 430.248 gives 28 A at 230 V, so conductors need
28 x 1.25 = 35 A: 8 AWG in NM-B, or 10 AWG at 75 C, which is 35 A exactly. The breaker ceiling is28 x 2.50 = 70 A. Powermatic recommends 30 A for its 5 HP single-phase PM2000B, rated 21 A. - Three-phase saws. They use Table 430.250, not 430.248.
- Long runs and hot spaces. Cerrowire's figures carry no temperature correction or adjustment. A run through a hot attic or bundled with other circuits can need larger wire.
- The 75 C column. It applies only where the wire type is listed in it and the breaker and receptacle terminals are rated for it. Check the device markings before counting on 12 AWG at 25 A.
- Local amendments. Everything here is the NEC as published. Local codes take precedence, as Powermatic notes, and Grizzly says wiring must be done by an electrician or qualified service personnel.
- Published figures only. Nameplates, circuit sizes and plugs come from the makers' listings and manuals, not from any saw on any circuit.
The thirty-second check
- Read the horsepower and voltage, not the amps. For 3 HP at 230 V single phase, the circuit current is 17 A.
- Wire for 21.25 A: 10 AWG in NM-B, or 12 AWG only where the 75 C column applies to the whole run.
- Pick a breaker from the maker's figure up to 45 A. 15 or 20 A is what the makers ask for.
- Match the receptacle to the breaker: 6-15 for 15 A, 6-20 for 20 A, 6-30 for 30 A. Change the saw's plug to match the receptacle, never the other way round with an adapter.