Why This Even Matters
Here's the situation we see every week: Someone buys a beautiful Bridgeport mill or scores a deal on a used CNC, gets it home, and realizes the machine needs three-phase power. They call the utility, get quoted somewhere between $10,000 and $50,000 to run 3-phase service, and suddenly that great deal doesn't look so great.
That's where phase converters come in. But first, let's talk about what makes single-phase and three-phase power different — because understanding this makes everything else click.
Single-Phase (What You Have)
This is standard residential power — two hot wires delivering electricity in one wave pattern. Fine for lights, refrigerators, and most home tools. Not enough for serious industrial motors.
Three-Phase (What You Need)
Three hot wires, each carrying current that peaks at different times. The power never drops to zero — it's constant and smooth. That's why industrial equipment loves it and runs cooler on it.
Think of single-phase like a one-cylinder engine — it works, but there's a lot of vibration. Three-phase is like a smooth inline-six where the power pulses overlap. Your motors run quieter, cooler, and last longer.
How a Phase Converter Actually Works
A rotary phase converter is basically a generator that creates the missing third phase. There's no magic here — just good old electromagnetic induction doing its thing. Here's the process:
Your Single-Phase Goes In
Standard 230V single-phase from your panel connects to the converter. Two hot wires in, just like any other 230V circuit in your shop.
The Idler Motor Spins Up
Inside the converter is a specially-wound three-phase motor we call the "idler." Start capacitors give it a kick to get spinning on your single-phase power.
The Third Phase Gets Generated
Here's where the magic happens. As that idler motor spins, electromagnetic induction in its windings creates a third phase of electricity. It's generating power, not just converting it.
Three-Phase Output to Your Equipment
Now you've got three hot legs, 120 degrees apart, just like utility three-phase. Hook up your machine and get to work.
The Three Types (And Which One You Actually Want)
You'll see three types of phase converters out there. Here's the honest breakdown — including the one we generally tell people to avoid.
Rotary Phase Converter
The workhorse. A real motor generating real three-phase power.
- ✓ Runs equipment at full rated power
- ✓ Works with any 3-phase load
- ✓ Balanced, clean output
- ✓ Can power multiple machines
- ✓ CNC-safe
- ✓ Lasts 20-30 years easy
Digital Phase Converter
Electronic power conversion — no spinning motor inside.
- ✓ Compact size
- ✓ No moving parts
- ✓ Quiet operation
- ✗ Not good for CNCs
- ✗ Problems with VFDs
- ✗ Higher cost, more limitations
Static Phase Converter
Just capacitors. Gets motors started, that's about it.
- ✓ Cheapest option
- ✓ Simple to install
- ✗ Only 2/3 power while running
- ✗ Unbalanced — hard on motors
- ✗ Will damage CNC electronics
- ✗ For starting motors only
Our take: Rotary is the way to go for most shops. Static converters are cheap for a reason — they'll shorten motor life. Digital converters look nice on paper, but they cause issues with VFD-controlled equipment and CNCs. We've seen too many headaches from digital units to recommend them for serious work.
Why Use a Phase Converter Instead of Utility 3-Phase?
The Math Just Works
A good rotary converter runs $1,500–$4,000 for most shop applications. Getting the utility to bring in 3-phase? We've seen quotes from $12,000 to over $60,000 depending on how far you are from existing lines. Plus you'll pay monthly demand charges forever.
You're Not Stuck Waiting
Utility work takes months — permits, scheduling, inspections. A phase converter? Install it in an afternoon, be making chips by dinner. We've helped a lot of guys get their new machines running the same week they arrived.
Put Your Shop Anywhere
Rural property? Residential neighborhood? Rented space where the landlord won't upgrade the service? Doesn't matter. If you've got 230V single-phase, you can run three-phase equipment.
Voltage Options
Got a mix of 230V and 460V equipment? Some of our converters give you both outputs from your single-phase 230V input. One converter, whole shop covered.
What People Are Actually Running
Pretty much anything with a three-phase motor. Here's what we see most often:
Common Questions
How do I know what size converter I need?
Start with your biggest motor. If you're running a 10HP compressor, you need at least a 10HP converter. Running multiple machines at once? Add up what'll be running simultaneously. For CNC equipment, go 25-50% bigger than the spindle motor rating — those servos draw extra power. Not sure? Call us with your equipment list and we'll figure it out together.
Can I run my whole shop off one converter?
Yep, that's how most people do it. Size the converter for your total running load, wire it to a 3-phase subpanel, and run all your equipment from there. Way simpler than buying a converter for each machine.
Will this work with my CNC?
Rotary converters — absolutely. We have customers running Haas, Fadal, Mazak, you name it. Static converters? Hard no. The unbalanced voltage will fry your drives. Digital converters? Also not recommended — they don't play nice with VFD-controlled equipment, which includes most modern CNCs. For CNC machines, stick with a properly sized rotary.
How hard is installation?
If you're comfortable with electrical work, it's straightforward — a few hours for most setups. Wire your single-phase input from a properly sized breaker, connect your equipment to the output terminals, done. That said, if you're not confident working with 230V, hire an electrician. We include detailed instructions and our guys are available by phone if you get stuck.
How long do these things last?
We've got customers running Phoenix converters from the 1990s with zero issues. The idler motor is a heavy-duty industrial unit — it just spins. Not much to wear out. We warranty ours for 5 years, but honestly, if you don't abuse it, 20-30 years is normal.
Is the power actually as good as utility three-phase?
From a properly sized rotary converter? Your equipment can't tell the difference. The third leg is generated power, same as what the utility would deliver. Some utility power is actually worse — we've seen shops switch TO converters because their utility three-phase was so dirty.
Not Sure What You Need?
Tell us what equipment you're trying to run. We'll help you figure out the right converter — no pressure, no BS.