If you run a CNC machine shop, you already know the challenge: your equipment demands three-phase power, but your building only has single-phase utility service. It's one of the most common problems we solve at Phoenix Phase Converters — and the good news is, a rotary phase converter makes it entirely manageable.

This guide walks you through exactly how to size and install a phase converter for CNC equipment, including the real-world considerations that separate a smooth installation from a frustrating one.

Why CNC Machines Need Special Attention

CNC machines — routers, mills, lathes, plasma cutters, and timber machines — are what we call a hard load. Unlike a simple motor that starts and runs at a steady draw, CNC equipment has variable load cycles. The spindle motor, servo drives, coolant pump, and axis motors all draw power at different moments, and inrush currents during startup can be significant.

One of our recent customers, an electrical engineer helping a client bring a 30 HP CNC timber machine online, ran into exactly this issue. The machine had only single-phase service available at the facility, and the OEM required true three-phase for the spindle drive and control system. A standard undersized converter would have caused voltage sag on the generated leg — leading to drive faults, erratic behavior, and premature drive failures.

The solution: a properly oversized GP series rotary phase converter with AutoLink technology.

Sizing a Phase Converter for CNC Equipment

The general rule for CNC machines is to apply a 2x multiplier to the motor horsepower when selecting a phase converter. This accounts for hard starting, variable loads, and inrush protection.

Here's a quick sizing reference:

  • 5 HP CNC machine → GP10 or GP15 phase converter
  • 10 HP CNC machine → GP20 phase converter
  • 15 HP CNC machine → GP30 phase converter
  • 20 HP CNC machine → GP40 phase converter
  • 30 HP CNC machine → GP60 or GP75 phase converter
  • 50 HP CNC machine → GP100 phase converter

If you're running multiple CNC machines on a single converter, add up the total horsepower and apply the 2x multiplier to the largest machine, then add the full HP of each additional machine.

How AutoLink Makes a Difference for CNC Loads

Phoenix Phase Converters come standard with AutoLink — our automatic load balancing system. This is especially important for CNC applications.

Here's why: CNC machines constantly shift their power draw as they move through a cutting cycle. Axis motors accelerate and decelerate. The spindle changes speed between operations. Coolant pumps kick on and off. Without active load balancing, the generated leg voltage can drift — causing voltage imbalance that trips VFDs, servo drives, and PLCs.

AutoLink continuously monitors and adjusts the output voltage on all three phases, keeping balance tight even as your machine cycles through different operations. The result is cleaner power, fewer nuisance faults, and longer life for your expensive CNC electronics.

Installation Tips for CNC Phase Converter Setups

  • Dedicate a circuit to the converter: Run a properly sized single-phase feed directly from your panel to the phase converter. Avoid sharing this circuit with other large loads.
  • Mount near the equipment: Shorter three-phase runs from converter to machine reduce voltage drop. If the converter must be remote, consult us about wire sizing.
  • Check your panel capacity first: A 30 HP converter on single phase draws roughly 150–170 amps at 240V. Make sure your service entrance can handle it.
  • Use a properly rated disconnect: Install a fused disconnect between the converter and your machine as a safety measure and to meet NEC requirements.
  • Let the converter idle between jobs: GP series converters can run unloaded — there's no need to shut down between CNC cycles.

Why Choose Phoenix Phase Converters for Your CNC Shop

Our GP series rotary phase converters are built in the USA in Phoenix, Arizona, using TEFC cast-iron motors and NEMA 4 enclosures. Every unit ships with a lifetime warranty — not a 1-year limited warranty, not a 5-year warranty, but lifetime coverage for as long as you own the converter.

For CNC applications, that reliability matters. You're not just protecting a motor — you're protecting the drives, tooling, and production schedules that keep your shop running.

Ready to Power Your CNC Machine on Single Phase?

Whether you're converting a single CNC router or equipping an entire machine shop, our team can help you size the right unit for your specific equipment and service.

Call us at 800-417-6568 or visit phoenixphaseconverters.com to talk through your application. We've been helping CNC shops solve the single-phase problem for decades — let us help you get your machines running.