What Size Phase Converter for a 5 HP Motor? 8 Makers' Answers

A 5 hp motor needs a phase converter labeled anywhere from 5 hp to 15 hp. American Rotary's FAQ and Phoenix's sizing guide both say to use a converter rated at twice the motor's hp. For a 5 hp table saw, lathe or mill, that's 5 x 2 = 10 hp.

Machines that are hard to start, like a piston compressor or a dust collector with its heavy fan, need more than 2x. Phoenix's sizing guide sizes a 5 hp piston compressor at 2.5 times its hp: 5 x 2.5 = 12.5 hp. The guide says to round up to the next size, and Phoenix's next size is 15 hp. For a 5 hp dust collector, Phoenix uses 3 times: 5 x 3 = 15 hp.

A unit labeled 5 hp may not start your 5 hp motor, because makers' labels count different things. At some makers, the label is the total load, meaning all the motors running at once. At others, it's the largest motor the unit starts. American Rotary's manuals list its 5 hp units for 5 hp of total load. Phase Technologies' Phase Perfect converters are digital, meaning electronic, and its manual rates them to start a motor as big as their label. So its 5 hp model starts a 5 hp motor. A rotary unit labeled 5 hp from Phoenix or North America Phase Converters (NAPCco) is rated to start a motor of 3 hp or less.

At Built for Production, we read eight phase converter makers' sizing documents and put each one's answer for a 5 hp motor on this page, with the math and the document it comes from. Figures are from the makers' documents as read in October 2026.

What size phase converter does each maker name for a 5 hp motor?

For a 5 hp saw or mill, two of the easiest machines to start, the makers' own rules and tables name units from 5 hp to 10 hp. Here's each maker's answer. All are rotary converters except the Phase Perfect PTS005, which is digital (solid state). Our guide to rotary vs digital phase converters vs VFDs covers why you'd pick one type over the other.

NAPCco's Need Help Sizing page sorts machines into four tiers by how hard they start: Easy, Medium, Hard and Very Hard. That page covers two of NAPCco's rotary lines, Pro-Line (PL) and Smart-Boost (SB). Ronk rates its converters in kVA (kilovolt-amperes, a measure of electrical capacity) instead of hp.

Where one maker's documents give two figures, we show both on this page. Ask that maker which applies to your machine before you order.

Two things about your motor can change these answers:

• An imported motor. Phase-A-Matic's sizing guidelines say Taiwanese, Chinese and Mexican motors need "a converter with twice the HP rating of the motor." ARCO's Standard Duty and "Heavy Duty" pages say to consult the factory for sizing on foreign motor designs.
• A two-speed motor or instant reversing. ARCO says to consult the factory for sizing on both. Phase-A-Matic's guidelines say a motor that reverses instantly needs a converter rated at twice its hp.

If your 5 hp machine runs alongside other 3 phase machines, the math changes. Our phase converter sizing guide walks through the makers' rules for several machines at once. If your biggest motor is 10 hp, our article on a phase converter for a 10 hp motor does the same work for that size.

Will a 5 hp phase converter run a 5 hp motor?

A unit labeled 5 hp starts a 5 hp motor at Phase Technologies and at ARCO, whose 5 hp unit is the HD5. At Phoenix, and on NAPCco's PL-5 and SB-5 rotary units, it starts a motor of 3 hp or less. American Rotary's manuals give a load figure and its FAQ gives a starting figure; both are below the table. Before you buy a unit labeled 5 hp, check what its maker's own documents say it can start. This table lists what each maker's documents say about its 5 hp unit:

Two figures for what a 5 hp unit starts: American Rotary, Kay and Phase-A-Matic

American Rotary's manuals list the AR 5 and AD/ADX 5 at 2.5 hp under the heading "LARGEST LOAD FOR OPTIMAL PERFORMANCE HP" and 5 hp under "MAX TOTAL LOAD RUNNING HP." That first heading is about the largest load for best performance. It doesn't call 2.5 hp a starting limit, and the manuals give no starting figure. American Rotary's FAQ says, "American Rotary converters typically handle starting loads 3-4 times their rated horsepower for brief periods." Its example is that "a 10 HP converter can start motors up to 30-40 HP, though it cannot run them continuously at full load." Ask American Rotary how big a motor its 5 hp unit starts.

Kay's Sizing and Selection Tables list the MA-1 for a 5 hp largest motor. Its 2026 MA Series manual says, "Total 3 phase motor starting HP must not exceed 75% of the rated HP of the converter." On the 5 hp MA-1, that's 5 x 0.75 = 3.75 hp, short of a 5 hp motor. Kay names no bigger unit for a 5 hp motor under that 75% line, so ask Kay.

Phase-A-Matic's instruction sheet rates the R-5 for a 3 hp largest motor at 230V. Its separate sizing guidelines name machines that start easily, such as a mill with step-pulley speed change or a lathe with a clutch. For those machines with an American-made motor, the guidelines say a converter "May be used up to the HP rating of the converter." By that line, the R-5 covers a 5 hp motor on those machines.

What size phase converter for a 5 hp table saw, planer, lathe, dust collector or air compressor?

For a 5 hp saw, jointer, planer, shaper, mill or lathe, the makers below name a converter of 5 to 10 hp. For a 5 hp dust collector or piston compressor, the rotary converter makers name 10 to 15 hp.

Three makers name a size by machine type. This table puts their answers side by side for each 5 hp machine. For NAPCco, we took each machine's tier from its Need Help Sizing page, then the smallest unit that page lists for a 5 hp motor in that tier.

"Not named" means the documents we read give no figure for that machine. Phase-A-Matic's 1.5x rows come from its guidelines' line for woodworking saws and lathes without a clutch: "Use a converter with HP rating of at least 50% larger than HP of the motor."

Phoenix's Sizing Wizard uses 1.5x for saws and milling machines, which gives 7.5 hp. Phoenix's GP7NL page rates that 7.5 hp unit to start a motor of 3 hp at most. So by Phoenix's product pages, its 7.5 hp unit isn't rated to start a 5 hp saw or mill. Its GP10NL page says "Start Motors up to 5 HP."

The other makers don't sort machines this way:

• American Rotary: 2x for every machine, so 10 hp. For compressors, its FAQ adds, "For hard-starting loads (compressors, punch presses), add 25-50% capacity." It doesn't say whether to add that to the motor's 5 hp or the converter's 10 hp. By our arithmetic, adding it to the 10 hp gives 12.5 to 15 hp. Its AD/ADX manual lists no size between 10 and 15 hp, so that points to its 15 hp unit.
• Phase Technologies: no separate rule by machine, so its answer stays the PTS005.
• Ronk: its Type 2P table has easy-start and hard-start columns. The 10 kVA unit starts a 5 hp motor on an easy start, and the 15 kVA unit starts 5 hp on a hard start. Ronk doesn't say which machines count as hard.

How many amps does a phase converter for a 5 hp motor need?

Makers publish three different kinds of amp figure for a converter that fits a 5 hp motor, so compare like with like. Input current is what the unit draws from your panel. A breaker range is the size of breaker the maker allows on the circuit feeding the unit. A service size is the smallest electrical service, measured in amps at your main breaker, that the maker says you need for the unit. A 31 A input current and a 100 A service size are different kinds of number.

Your electrician sizes the wire feeding a converter from the input amps on the converter's nameplate, according to EC&M's summary of National Electrical Code (NEC) Article 455.

Each maker publishes these figures for its own units that fit a 5 hp motor:

A licensed electrician sizes every install to the NEC and local code.

If your house or barn has a 100 A panel, that's the same as Phoenix's 100 A service size for its GP15NL alone. Talk to your electrician before you order, and ask:

• Does my service have room for this unit's input amps with the rest of the house or shop running?
• What does the maker's manual call for on breaker and wire for this exact model, and does local code change that?
• Do I need a permit or an inspection here?

A 5 hp 3 phase motor at 230V draws about 13 A at full load. That's its FLA (full load amps), the figure printed on the motor nameplate. Three Baldor catalog motors print 13.4 A (EM3615T and CEM3615T) and 13.2 A (EM3665T). Your own nameplate has the real figure, and you'll need it for the VFD math below.

Can a VFD run a 5 hp motor on single phase power?

A VFD (variable frequency drive) can run a 5 hp 3 phase motor from single phase power, one motor per drive. Phoenix's guide to converters for CNC machines says a VFD "Cannot power multiple motors simultaneously." If your machine has a second motor, such as a coolant pump or a power feed, one drive won't run both. For several machines, look at a converter.

A drive built for single phase input

Invertek's Optidrive E3 ODE-3-320153-1042 is one drive built for this. Its datasheet lists it at 4 kW (5 HP), with 200 to 240V single phase in and 3 phase out. It puts out up to 15.3 A to the motor, which covers the 13.2 to 13.4 A FLA of the Baldor motors above. Check your own nameplate FLA against any drive's output current. Its input is a separate figure. Invertek lists a continuous supply current of 29.2 A, which is what the drive draws from your panel. Your electrician needs that one.

A 3 phase drive run below its rating

The other way is to feed single phase to a drive built for 3 phase input. That drive has to be rated above the motor. Yaskawa's application note AN.AFD.15 says why: "single-phase use requires the three-phase VFD power rating be reduced (derated)."

Lenze's application note on derating VFDs for single phase input gives a rule: "VFD Input Current > Motor Current Rating * 1.73." With a 13.4 A motor like the Baldor EM3615T, that's 13.4 x 1.73 = 23.18. So the drive's input current rating has to be at least 23.2 A. TECO-Westinghouse takes a stricter line in its E510 instruction manual: "Please consult the factory when applying single phase input for all models rated 230 & 460V 5HP and above."

If your machine has its own 3 phase controls, such as a reversing switch or a magnetic starter, ask the drive maker whether its drive suits them before you buy. If the machine is a compressor, our article on a VFD for an air compressor covers that case.

Will a static phase converter run a 5 hp motor?

A static converter runs a 5 hp motor at reduced power. Phase-A-Matic's UL Series brochure says its static converters run a wye-wound motor at 2/3 of rated hp and a delta-wound motor at 50%. On a 5 hp motor, that's about 3.3 hp or 2.5 hp. Wye and delta are two ways a motor's windings are connected inside. The motor's maker can tell you which yours has.

A static converter runs one machine at a time, per Phoenix's article comparing static, rotary and digital converters. Phase-A-Matic's brochure says some loads "will not work" on its static converter, including some air compressors, pumps, blowers, fans and 3 phase electronic controls such as CNC. NAPCco's Need Help Sizing page marks piston air compressors "Static Converter not recommended." Our static phase converter guide covers the trade-offs.

What should you have ready before you order?

Have these ready before you run the numbers or call anyone:

• Motor hp from the nameplate, for every motor on the machine
• Voltage: 230V, 460V, or dual voltage like 230/460
• FLA at the voltage you'll run
• What the motor drives: saw, jointer, planer, lathe with or without a clutch, mill, dust collector, piston compressor
• Where the motor was made, and whether it's two-speed or reverses instantly
• Other 3 phase machines that run at the same time
• Your single phase service in amps, from the main breaker

Our phase converter sizing calculator takes the machine type, the motor hp or its FLA, the total hp running at once, the machine voltage and your service amps. It applies American Rotary's, Phoenix's, NAPCco's and Phase Technologies' published rules and names the document for each.

Want the math run on your nameplate?

Call us at (855) 923-2610 or email contact@builtforproduction.com with a photo of your motor nameplate. We'll run it through each maker's published rule and show you the arithmetic. You can also reach us through our contact page.