How to Run 3 Phase Machines on Single Phase Power

You can run a 3 phase machine on single phase power. Four devices do it: a static phase converter, a rotary phase converter, a digital phase converter, or a VFD (variable frequency drive) with single phase input. A transformer is not one of them. Hammond Power Solutions' FAQ says: "Transformers cannot convert a single-phase source to a three-phase source."

Which of the four fits your shop comes down to four things: how many machines run at once, the horsepower of the largest motor, whether the machine has a CNC or other electronic control, and what your single phase service can carry. At Built for Production, we put each maker's published sizing rule beside your machine and show the arithmetic. This guide walks through the choice. The sizing guide and the sizing calculator do the math.

Can you convert single phase to 3 phase?

Yes. The four ways make the third leg differently, and that sets what each can run.

Static converters are shown here for comparison.

What do you need to know before you pick?

Write down four things for every 3 phase machine you own or plan to buy.

• The motor nameplate: horsepower, volts and full load amps (FLA). Nameplate amps show the running load, not the starting load. Phoenix's article on sizing by amps says the nameplate "usually shows the running load, not the starting load".
• How many motors the machine has, and how many machines run at the same time. A lathe with a coolant pump and a power feed has three motors.
• The kind of load. Phoenix's sizing guide sorts loads into standard (lathes, mills, drill presses, fans, centrifugal pumps, screw compressors, saws), hard-starting (piston compressors, scroll compressors, loaded conveyors, submersible pumps, hydraulic presses, equipment that starts under load) and high-inertia (dust collectors, large industrial fans, flywheel-driven equipment).
• Your single phase service size at the panel, in amps. Your electrician reads it off the main breaker.

Phoenix's amps article lists what converter size depends on: "horsepower, starting load, equipment type, voltage, motor quantity, heating elements, and how the machine operates."

Which of the four ways fits your shop?

One machine with one motor: a VFD with single phase input

A VFD takes single phase in and runs one 3 phase motor, with speed control. Phoenix's CNC guide: "VFDs work well for single-motor applications like spindle-only conversions". The catch is the ceiling. Lenze's application note on derating VFDs for single phase input: "Most manufacturers of VFDs only offer products up to 3 Horsepower (HP) for single phase input." Invertek's Optidrive E3 specification lists 230V single phase input at 0.37 to 4 kW (0.5 to 5 hp).

Above that ceiling you can feed a larger 3 phase drive with single phase, but the drive maker's own derating rule applies. Yaskawa's application note AN.AFD.15: "single-phase use requires the three-phase VFD power rating be reduced (derated) to avoid over stressing the rectifier and DC link components." Each drive maker publishes its own rule, and they differ. If the machine has its own starter, contactors or controls, ask the drive maker before you buy.

See VFDs with single phase input.

Several machines, or a machine with several motors: a rotary phase converter

A rotary converter feeds a 3 phase panel, and every machine on that panel runs from it. Phoenix's comparison guide: "one rotary converter can power your entire shop". American Rotary's FAQ sizes a shop with a 10 hp lathe, a 5 hp mill and a 3 hp dust collector this way: "10 + 5 + 3 HP= 18 HP minimum. We'd recommend a 40 or 50 HP unit for headroom."

A rotary converter has a motor inside, so it makes noise. Phoenix's noise article: "All of our phase converter models produce 43 Db from ten feet away." American Rotary's FAQ gives 60 to 70 dB for every size and states no distance. The two figures come with different conditions, so we don't compare them on one line.

See rotary phase converters.

A CNC or another voltage sensitive machine: compare the published balance figure

A CNC control cares how close the three legs sit to each other. Your CNC maker's manual says what its control accepts. The converter makers publish these figures:

We promise nothing beyond the converter maker's published figure. See digital phase converters.

One light-duty machine on the smallest budget: a static converter

A static converter starts the motor, then drops out. American Rotary's CNC page: "once an electric motor has been started, the static phase converter will disengage and allow the electric motor to run only on single-phase power." You get about two thirds of the motor's horsepower (Phase-A-Matic's figure for its Method No. 1), one machine at a time. Phoenix's comparison guide: "Static converters cannot run CNC machines, sensitive electronics, or any equipment requiring balanced three-phase power." NAPCco's motor load chart marks piston and rotary screw air compressors, and several pump types, "Static Converter not recommended".

The full trade-off is in Static phase converters and the horsepower trade-off.

What size converter do you need?

It depends on whose unit you buy. Each maker publishes its own rule for its own units, and the rules don't agree.

• American Rotary's FAQ: "Choose a converter rated at least twice the Horsepower rating of your load." For hard-starting loads, "add 25-50% capacity."
• Phoenix's sizing guide: 2× the largest motor for standard loads, 2.5× for hard-starting loads, 3× for high-inertia loads. "Always round up to the next available converter size."
• NAPCco's sizing page rates each unit by how hard the load starts. Its PL-10 carries 7.5 hp at Easy, 6 hp at Med, 5 hp at Hard and 4 hp at Very Hard.
• Phase Technologies' Gen4 manual rates a Phase Perfect to start a motor up to its own nameplate horsepower, except 50 hp models and larger.

For a 5 hp manual lathe, that gives 10 hp under American Rotary's rule and 10 hp under Phoenix's, an NAPCco unit whose chart row covers 5 hp at the tier NAPCco assigns a lathe, and a Phase Perfect with a 5 hp nameplate or more. The sizing guide works through five examples. The calculator applies every rule to your numbers.

Why is one "10 hp" converter different from another?

Makers rate their units on different bases, so the model number is not the motor it starts.

Compare the maker's largest-motor figure for your load, not the model number.

Who installs it, and do you need a permit?

A licensed electrician installs it. The makers say so in writing. American Rotary's AD(X) owner's manual: "Installation should be done by a licensed electrician who is familiar with phase converter installations." Phoenix's installation guide: "Phase converter installation should always be performed by a licensed electrician." Phoenix's warranty page excludes "installations not compliant with local electrical codes". We don't give wiring instructions.

Ask your local inspector before you order. American Rotary's UL page: "If you are having your installation inspected by your local inspector, it's important to check with them prior to ordering your phase converter to see what is required to pass inspection." Phoenix's installation guide names NEC (National Electrical Code) Article 455 as the article that covers phase converter installs.

Where it sits: Phoenix's installation guide puts a converter in an indoor or covered area, protected from rain and direct weather, in a well-ventilated space because the converter makes some heat, and near the electrical panel because shorter wire runs cost less and reduce voltage drop.

Is your single phase service big enough?

A converter's input breaker has to fit your service. American Rotary's FAQ publishes minimum single phase service for its own units: "Min of 20 AMP" for its 5 HP converter, "Min of 40 amp" for 10 HP, "Min of 60 amp" for 20 HP, "Min of 150 amp" for 50 HP and "Min of 200 amp" for 75 HP. Other makers' units differ. A licensed electrician sizes every install to the NEC and local code. If your whole shop runs on a 100 A service, ask your electrician whether it can carry the converter before you order.

What arrives on the truck?

A phase converter ships on a pallet by LTL freight (less than truckload, a freight truck). Small drives ship by parcel. Before you sign the delivery receipt, look at the crate on all sides and write any damage on the receipt. The freight delivery checklist covers delivery day, and the Shipping page holds the terms.

When should you stop and call the maker's engineers?

Some setups sit outside what a sizing rule settles. Stop and ask before you buy if you have any of these:

• A 480V machine on 240V service. Phoenix's 480V page: "On its own, a rotary phase converter produces a three-phase voltage that matches the input voltage." Its answer is a rotary converter plus a step-up transformer. The maker's engineers size that package. Can a transformer make 3 phase from single phase? covers the transformer question.
• An elevator. NAPCco's elevators page: "Some elevators have strict voltage balancing modulation systems, requiring as tight as +/- 3% voltage balance between phases."
• A regenerative load, one that drives the motor back, such as a lowering hoist. Phoenix's digital vs rotary article rates VFD-based units "Generally troublesome to use" there. That is one rotary maker's claim about the other design.
• Heating elements, such as a grain dryer or an oven. Phoenix's amps article: "Heating elements do not have starting inrush like a motor, but they add a steady electrical load."
• A fire pump, or a medical or life safety load. A 2014 Electrical Contractor magazine article reports that "Section 695.3(G) prohibits the use of phase converters for fire-pump service." We give no advice on either.

Call (855) 923-2610 and we point you to the maker's engineers with their published number. Service size, permits and code go to a licensed electrician and your inspector.

Questions

How do you get 3 phase power at home?

With a phase converter or a VFD on your existing single phase service. A rotary or digital converter feeds a 3 phase panel for several machines. A VFD with single phase input runs one motor, most lines up to 3 hp (Lenze's application note on derating VFDs for single phase input) and Invertek's E3 up to 5 hp. The utility can also bring 3 phase service to the building; ask the utility for that quote.

Can a transformer make 3 phase from single phase?

No. Hammond Power Solutions' FAQ: "Transformers cannot convert a single-phase source to a three-phase source." A step-up transformer changes voltage, for example 240V to 480V, after a converter has made 3 phase.

Which way is the cheapest?

A static converter has the least in it, and it gives you about two thirds of the motor's horsepower, one machine at a time (Phase-A-Matic's Method No. 1 figure; Phoenix's comparison guide). For one motor under 3 hp, a VFD with single phase input is the other small answer. Above that, a rotary converter sized by the maker's rule. We don't print prices in guides; each maker's list changes.

Sources named in this guide

Hammond Power Solutions' FAQ on converting single phase to three phase (linked above). Phoenix Phase Converters' comparison guide (static vs rotary vs digital), sizing guide, CNC guide, installation guide, warranty page, noise article, article on sizing by amps alone, 480V page and digital (VFD) vs rotary article. American Rotary's phase converter FAQ, phase converter for CNC page, UL listing page and AD(X) owner's manual. North America Phase Converters' (NAPCco) sizing page and elevators page. Phase Technologies' Phase Perfect Gen4 manual and DPC series manual. Phase-A-Matic's static converter instruction sheet. Lenze's application note on derating VFDs for single phase input. Invertek's Optidrive E3 specification. Yaskawa's application note AN.AFD.15. Electrical Contractor magazine, June 2014, on phase converters and fire pumps. We name maker documents and don't link maker sites.

Not sure which way fits? Run your numbers through the sizing calculator, or call (855) 923-2610 with the motor nameplate: horsepower, volts and full load amps.