What to Know Before Sizing a Rotary Phase Converter

Five pieces of information are all you need for an accurate size.

The 5 Inputs

  1. Equipment type: CNC, compressor, lathe, HVAC, pump, saw — determines the multiplier.
  2. Horsepower: HP rating of the largest motor. Found on the nameplate.
  3. Voltage: 230V or 460V three-phase? Check the nameplate.
  4. Simultaneous loads: Multiple motors running at once? Add their HP.
  5. Special conditions: Dusty shop (NEMA 4)? Compressor or HVAC (NLA AutoLink)?

Load Multipliers

Equipment Multiplier
Saws, grinders, drill press 1.0x
Lathes, mixers, centrifugal pumps 1.5x
CNC, pumps, press brakes 2.0x
Compressors, HVAC, fans 2.5x

Examples

  • 10 HP compressor: 10 x 2.5 = 25 HP - GP25NLA
  • 10 HP CNC: 10 x 2.0 = 20 HP - GP20NL
  • 10 HP grinder: 10 x 1.0 = 10 HP - GP10NL

Not sure? Call (800) 417-6568 — free sizing, no obligation.

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Sizing — FAQ

What if I have multiple motors running at different times?

Size for the largest motor that will ever run, using the correct multiplier. If multiple motors run simultaneously, add their HP and apply the multiplier for the hardest-starting one.

Is it better to oversize a phase converter?

Yes — a converter running at 60–70% of rated capacity runs cooler, generates better voltage balance, and lasts longer. Oversizing is never harmful.

What happens if I undersize?

Voltage sag on L3, nuisance breaker trips, sluggish motor starts, and long-term motor overheating. Undersize is the single most common cause of phase converter problems.

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Questions? Talk to an engineer.

Free sizing help. Made in Phoenix, AZ. Lifetime warranty on every unit.

Shop Phase Converters

(800) 417-6568