Can a Table Saw and Dust Collector Share a 15 Amp Circuit?

Two answers circulate. One says it works, because plenty of people do it and the breaker holds. The other says it cannot, because 15 plus 11 is 26. The arithmetic is right. The anecdote is also real, because a breaker is a heat-and-time device whose curve allows a short overload. Below, five saws and five extractors are paired, summed, and placed on the trip points the breaker standard actually sets.

The 80 percent cap: one saw is already over it

The rule is in NEC 210.23, "Permissible Loads, Multiple-Outlet Branch Circuits". In the 2023 edition it sits at 210.23(B)(1), "Cord-and-Plug-Connected Equipment Not Fastened in Place", under "(B) 15- and 20-Ampere Branch Circuits". The 2020, 2017 and 2014 editions number the same provision 210.23(A)(1): the 2023 edition inserted a new (A) and moved the rest down a letter. The wording has been stable for decades. The 1999 code, as quoted in a task group's proposal to NFPA, reads: "The rating of any one cord- and plug-connected utilization equipment shall not exceed 80 percent of the branch-circuit ampere rating."

So the headline question fails on the saw alone: a 15 A jobsite saw on a 15 A circuit that feeds other receptacles is over 210.23 by 3 A. The cap is per item, not a total. It does not let a 20 A circuit carry a 16 A saw and a 12 A collector; the total is limited by the breaker.

The same 1999 submittal shows why saws are built to their plug's full rating anyway. Its table lists power tools among equipment using plugs at 100 percent of the plug rating, as intermittent duty, against continuous duty for vacuum cleaners and air compressors. A 15 A saw on a 15 A plug is normal. What 210.23 limits is a 15 A circuit that other loads share.

What the saws and the extractors draw

Five 120 V saws, from two jobsite saws to two 2 HP hybrids, with the current each maker prints:

Grizzly is the only maker here that prints a circuit for a 120 V saw, and both figures are 20 A, consistent with the 12 A cap. Its 15 A G0771Z draws the same as the two jobsite saws.

And five extractors:

Festool prints power, not current, so its 10 A is 1,200 W / 120 V. All five fit a 15 A circuit on their own, at or under 12 A.

Ignore a vacuum's horsepower. Shop-Vac's own sheet says "Shop-Vac motors do not operate at the peak horsepower shown." Its 12 A is the figure that loads the circuit.

Every pair, summed against 15 A and 20 A

Three saw currents against four extractor currents, as a share of each breaker:

Worked for the Jet collector and a jobsite saw: (15 + 11) / 15 = 1.73.

The lightest pair, a 14 A saw and the 7 A Grizzly G1163P, is 21 A: over 15 A by 6 A and over 20 A by 1 A. Not one combination fits either circuit. On 120 V, a table saw and a dust collector are two circuits' worth of load.

Why the breaker often holds anyway

A residential breaker has two trip mechanisms, and neither opens at the rating. Goodson, Hergenrether and Stateson, in Fire and Arson Investigator, list that belief first among breaker myths.

The thermal element follows a time curve. UL 489, the standard residential breakers are listed to, sets three calibration points, as summarized by OptiFuse: hold at 100 percent of rating, trip within one hour at 135 percent (breakers of 50 A and under), and trip within two minutes at 200 percent (30 A and under). Goodson and co-authors give the same 135 and 200 percent points from NEMA AB-1, and add that "at even 5 percent above trip rating, there is no guarantee that the breaker will ever trip."

Read the sums above against those three points:

No pair here reaches 200 percent of a 15 A breaker, so the standard's only requirement for every one of them is a trip within an hour. A 40 second rip can finish well inside that, and nothing is wrong with the breaker. On a 20 A breaker most pairs sit under 135 percent, where UL 489 sets no trip time at all.

Makers' published curves are usually faster than the standard allows, Goodson and co-authors note, so a real breaker at 173 percent will normally trip well inside the hour. Their Square D 30 A breaker at 60 A, 200 percent, tripped in 30 seconds at 20 F and 21 seconds at 69 F. A panel in a hot garage runs closer to its trip point, one reason the same pair can run in January and trip in July.

The full-load figure is a full-load figure. Grizzly defines full-load current as "the amperage a machine draws at 100% of the rated output power." A saw spinning between cuts is not at rated output, so the sum is the moment both machines work at full load together. Grizzly adds the other side: it "is not the maximum amount of amps that the machine will draw," and an overloaded machine draws more, as in a slow rip through thick hardwood.

The starting surge, and why starting order matters

A motor draws far more than its running current for the moment it starts. Honda's generator catalog lists a 10 in table saw at 4,500 W approximate starting wattage against 1,800 W running. Divided by 120 V, that is 4,500 / 120 = 37.5 A at start, 2.5 times the 15 A rating, if the starting load is drawn at 120 V.

That surge mostly meets the breaker's other mechanism. The magnetic, or instantaneous, element responds to large currents with no intentional delay. Goodson and co-authors stress that NEMA AB-1 "does not specify a required magnetic trip level", so each maker sets its own. One example they describe is a 20 A breaker with an instantaneous trip level of 180 A. Against that example:

A saw start is far below the magnetic trip in that example and, if brief, over before the thermal curve acts. That is the second reason a shared circuit often survives.

Starting both motors at once stacks two surges. No collector maker here prints a starting current, but the order is free: start the collector, let it reach speed, then start the saw. The same applies on a generator, where the generator guide for a 15 amp table saw sizes the saw at 4,500 starting watts. Add the Jet collector running at 11 x 120 = 1,320 W and the generator needs 5,820 W at the saw's start, if the collector is already on.

Not tripping is not the same as safe

A breaker that holds is not a verdict on the load. Three things carry the 26 A that the breaker is not watching:

• The cords. A residential breaker "is not intended to protect load wiring such as extension cords or appliance line cords," Goodson and co-authors write. The extension cord gauge guide quotes the makers' rule to add the nameplate amps of every tool on one cord, and finds a 21 A load covered by no table at any length. A tool-triggered outlet on a vac puts both currents through the vac's cord and one wall receptacle.
• The receptacle. A 15 A receptacle carrying 26 A is over its rating whether or not the breaker opens.
• The motors. Both motors see the voltage drop of both loads in the same wire, and that drop grows with current.

Grizzly's circuit sizes apply to a dedicated circuit, "where only one machine will be running on the circuit at a time." For a shared circuit, Grizzly says to consult an electrician.

What actually works

Two circuits. Saw on one 20 A circuit, collector on another. Every pair here fits: 14 to 16 A on the saw's circuit, under its 16 A cap, and 7 to 12 A on the collector's, under even a 15 A circuit's 12 A cap. A garage already needs at least one 20 A receptacle circuit under the NEC, as covered in garage shop layout, and that guide's advice to plan dedicated circuits before the wall system goes up applies to a collector as much as to a compressor, the other motor whose demand is set out in whether a bigger compressor tank gives more CFM.

Move the collector to 240 V. The Jet DC-1100VX draws 5.5 A at 230 V and the Grizzly G1028Z2 6 A at 240 V, half their 120 V current, on a separate double-pole circuit. That frees the 120 V circuit for the saw, and it is the same kind of run worked out in what size breaker and wire a 3 HP table saw needs.

A collector on a cart can roll to whichever circuit is free, the trade-off weighed in mobile workbenches against tool carts.

Where this answer stops applying

• 240 V machines. Every figure above is 120 V.
• An individual circuit to one single receptacle. 210.23 is written for multiple-outlet branch circuits, and this page does not cover the single-receptacle case.
• Other breaker types. GFCI and AFCI breakers add their own trip functions. Power strip breakers are thermal only, with no magnetic trip level.
• Local amendments and your breaker's curve. Local codes may differ, and a real breaker's curve is usually faster than the standard's limits.
• Published figures only. The currents are the makers' ratings. No saw, collector or breaker was run for this page.

The thirty-second check

1. Read the amps on the saw and on the collector or vac, and add them.
2. Compare the sum with the breaker. Any table saw and any extractor on this page sum to more than 20 A.
3. Check the saw alone against 80 percent of its circuit: 12 A on 15 A, 16 A on 20 A. A 15 A saw needs the 20 A circuit.
4. Put the collector on a second circuit, or on 240 V. Start the collector first, then the saw.
5. If the breaker holds anyway, that is the time curve at work, not a load within the circuit.