The most expensive mistake in buying industrial machinery has nothing to do with the machine. It is discovering, after delivery, that your building cannot power it.
This one is worth ten minutes of reading before you order anything.
Single-phase vs three-phase: the actual difference
Single-phase power delivers energy in pulses that cross zero 120 times a second. It is what residential and light commercial buildings have. It works fine for motors up to roughly 5HP.
Three-phase power delivers three overlapping waveforms, so power delivery never drops to zero. For motors this is a genuinely better arrangement:
- Smoother torque, less vibration
- Roughly 150 percent more power from the same frame size
- No starting capacitors to fail
- Longer motor life
- Lower running cost at the same output
This is why nearly all serious industrial machinery — large bandsaws, CNC equipment, big compressors, industrial dust collection — is three-phase. It is not manufacturers being awkward. Above about 5HP, single-phase stops being practical.
The voltages you will actually encounter
- 120V single-phase — hand tools and lighting. Nothing industrial.
- 208V three-phase — very common in commercial buildings and strip units. Note this is not the same as 230V.
- 230/240V single-phase — the standard for small shops and serious home shops. Runs machines up to about 5HP.
- 230/460V three-phase — the industrial standard in most shops.
- 480V three-phase — large industrial plant, big motors, high-capacity machinery.
The 208 vs 230 trap
Many machines are labelled 230V. Many commercial buildings supply 208V. That is a 10 percent shortfall, and while some motors tolerate it, running a 230V motor on 208V means it draws more current to make the same power, runs hotter, and dies early.
Check the motor's nameplate voltage range. If it says 208-230V you are fine. If it says 230V only, you have a problem worth solving before delivery, not after.
How to find out what you have
Open your electrical panel cover — or better, have an electrician do it — and look:
- Two hot legs feeding the main breaker → single-phase
- Three hot legs → three-phase
Then check the service capacity in amps, which is stamped on the main breaker. Having three-phase available means nothing if the service is already fully loaded. A 20HP machine on a 100A service is not going to work regardless of phase.
If you only have single-phase
You have three options, in increasing order of cost and decreasing order of compromise.
Rotary phase converter
A rotary converter generates a third leg using an idler motor. It works, it is well-proven, and it will run most three-phase machinery. Caveats: the generated leg is not perfectly balanced, you typically size the converter at 2 to 3 times the motor HP, and it runs continuously, consuming power and making noise.
Generally not suitable for CNC machinery or anything with sensitive electronics.
Variable frequency drive (VFD)
A VFD takes single-phase in and produces genuine three-phase out, and gives you variable speed as a bonus. It is the best-quality solution for a single machine. Sizing matters: a VFD fed single-phase must typically be derated to about 50 percent of its nameplate rating.
One VFD per machine. This is not a whole-shop solution.
Have three-phase brought in
If it is available on your street, this is the real fix. Cost varies enormously by distance to the transformer. Get a quote before assuming it is out of reach — shops are often surprised in both directions.
Generators as shop power
For temporary sites or shops without adequate service, a generator can be the answer — but it has to be the right one. A 480V three-phase unit is a different machine from a portable contractor generator, and you cannot adapt your way from one to the other. See our generator sizing guide for the calculation.
Before you order any machine, confirm
- Voltage and phase of the machine — from the nameplate spec, not the marketing copy.
- Full load amps, and whether your panel has capacity for that plus everything already on it.
- Whether the motor is dual-voltage — many are, and rewiring at the junction box is trivial.
- Breaker and wire sizing for the run. Long runs need heavier wire than the breaker alone implies.
If you tell us the machine you are considering and what your panel looks like, we will tell you honestly whether it will run — before you commit to it. Get in touch or request a quote and we will come back within 24 hours.