Running a three-phase spindle from a single-phase supply

It works, it is what most small machines do, and it costs you more supply current than people expect. Here is the arithmetic, and the one voltage limit you cannot engineer around.

Where the √3 comes from

Power in equals power out, so compare the two sides:

Three-phase output: P = √3 × V × I_out × cosφ
Single-phase input: P = V × I_in × cosφ

At the same voltage, that gives I_in ≈ √3 × I_out — about 1.73 times the current the drive is delivering to the spindle. Real drives add their own losses on top, so treat 1.73 as a floor, not an answer.

The practical consequence: the supply cable, the breaker and the socket feeding a 2.2 kW single-phase-input drive have to be sized for noticeably more than 2.2 kW worth of current at 230 V. People size for the spindle's nameplate and then wonder why the breaker is warm.

The voltage ceiling nobody can get around

A drive cannot output more voltage than it is fed. A single-phase 220 V input produces a 220 V three-phase output. A 380 V spindle connected to it will turn — weakly, badly, and it will draw excessive current trying to make torque. It is the single most common mismatch in this whole subject.

Your options, in the order worth checking:

Check whether the spindle is dual-voltage. Open the terminal box. Six leads and a nameplate reading 220 V Δ / 380 V Y means the windings can be linked for 220 V delta — then a 220 V drive runs it properly. See star and delta.
Buy a spindle wound for your supply. Usually cheaper than the alternatives once you price a transformer.
Step the voltage up. Either a drive that takes single-phase 220 V in and gives three-phase 380 V out, or a transformer ahead of a three-phase drive. Both exist; both cost more than buying the right spindle, and the transformer has to be sized for the full input current.
Get a three-phase supply, or generate it. Out of scope for a hobby machine in most cases.

Check the single-phase rating, not the headline rating

A drive is usually sold with a headline power figure, and a small line elsewhere giving what it manages on a single-phase input. They are frequently different, because the input rectifier and the DC bus capacitors are carrying √3 times the current they would on three phases. A frame sold as 4 kW may be rated substantially lower when fed single-phase.

Read the datasheet line that specifically says single-phase input. If it is not printed, ask — and treat silence as a reason to buy the next size up.

How far single-phase input goes

Single-phase-input drives are widely available through the small sizes and get progressively rarer and more expensive as power rises. Above the point where your supplier stops listing them, the sensible answer is a three-phase supply rather than a bigger transformer. We are not going to publish a boundary in kilowatts: it varies by maker, by region, and by what is in stock this year.

Protection: the RCD problem

Drives leak a little current to earth by design — the switching stage couples into the motor cable screen and the motor windings. Older types of residual current device cannot tell that from a fault, so they nuisance-trip. Two honest notes:

If your installation requires RCD protection, it generally needs a type that is rated for the waveform a drive produces. Which type applies is a question for your local wiring rules and your electrician, not for a website.
Do not solve nuisance tripping by removing protection. Solve it with the correct device.

Use the calculator. The VFD sizing calculator takes the nameplate and returns both the drive current class and the single-phase supply current, so you can spec the circuit in one go.

Parts

Drives

Questions

Can I run a three-phase spindle from a single-phase supply?

Yes — a VFD with single-phase input and three-phase output is the standard way. It is not free: the input rectifier and DC bus carry more current for the same output power, so drives are derated on single phase.

Why does the drive have to be bigger on single phase?

Only two of the three input legs conduct, so the current in them is roughly √3 times higher for the same output power, and the DC bus ripple current is worse. The headline rating is usually the three-phase one.

Will an RCD trip on a VFD?

It can. Drives leak high-frequency current to earth and a standard RCD may read that as a fault. What your installation requires is a question for your local rules and your electrician, not for this page.

Sources and method

Three kinds of statement appear on this page, and each is labelled where it occurs:

Derived — the derating arithmetic is shown on the page: input current rises because the DC bus draws its current in pulses, not sinusoidally.
Rule of thumb — workshop practice, not a standard. Given with the range it is meant to hold over, and it loses to your manual wherever the two disagree.
Maker-specific — parameter numbers, connector pin numbers, minimum brake resistance, maximum cable length, bearing speed limits. Not published here. They move between firmware revisions of the same model, and a wrong one is worse than none.

Standards and documents

IEC 61800-3 — adjustable speed drives: EMC requirements and specific test methods
IEC 61000-3-2 — limits for harmonic current emissions
NEMA MG 1 — motors and generators
The manual for your own drive and spindle — the only valid source for maker-specific values