3 Phase Voltage for Shop Machines: 208V, 230V, 240V and 480V

In the US, 3 phase power comes in three common voltages: 208V, 240V and 480V. Each number is the voltage between any two of the three hot wires coming into the building. A motor built for that power is rated a little lower: 200V for 208V power, 230V for 240V power, and 460V for 480V power. So a 230V motor is made for a 240V shop.

If your shop has single phase 240V, a rotary phase converter makes 3 phase at the same voltage it takes in, according to Phoenix Phase Converters' article on running 480V equipment from 240V. That gives you about 240V 3 phase, which suits a 230V machine. A machine rated only for 460V or 480V takes a different setup, covered below.

Built for Production is an online retailer of phase converters and VFDs (variable frequency drives). When you call us about what size converter or VFD you need, we ask for the motor's horsepower, voltage and full load amps from its nameplate, plus a few questions about the machine and the power coming into your shop.

How many volts is 3 phase in the US?

Most 3 phase power in the US runs at 208V, 240V or 480V between hot wires. The utility delivers it as one of several setups, called services. Each has a name the utility uses, such as 120/208V wye or 480V delta. Some include a neutral wire and some don't. The table shows the common US services, plus one less common service where one hot wire reads a higher voltage to neutral than the other two. The details come from the service types page of Continental Control Systems, a maker of power meters.

Why do 3 phase services have two numbers?

The first number is the voltage from any hot wire to the neutral. The second is the voltage between any two hot wires. On a 120/208V service, each hot reads 120V to neutral and 208V to each of the other two hots. Continental Control Systems says hot to hot is typically 1.732 times hot to neutral, so 120V x 1.732 = 208V.

A 3 phase motor connects only to the three hot wires and doesn't use the neutral. The neutral serves single phase loads, such as 120V outlets on a 120/208V service and 277V lights on a 277/480V service.

So if someone measures 277V between one hot and the neutral on a 277/480V service, the service is still 480V. The 480V reading is between two hots, and that's the voltage a 3 phase motor sees.

Is 3 phase 400V?

400V 3 phase is the European system, with 400V between hots and 230V from a hot to neutral, according to Continental Control Systems' table of international services.

Is 240V 3 phase?

Household 240V is single phase. Both hot wires come from one transformer coil, split at its center: 120V from either hot to neutral, and 240V between the two hots. A 3 phase motor needs three voltages that peak at different times, and two wires from one coil can't supply that.

240V 3 phase does exist as a delta service: three hot wires with 240V between any two, found mostly in industrial and older manufacturing buildings. Our post Is 240V single phase or 3 phase? explains household 240V in more detail.

Why does my motor nameplate say 230V or 460V?

Motors are rated a little below the voltage the utility delivers, because some voltage is always lost in the wire between the utility's transformer and the motor. Dale Basso, then a motor product specialist at Reliance Electric, explained it in Machine Design: "The voltage rating assumes that there is voltage drop from the network to the motor terminals."

The U.S. Department of Energy's tip sheet on motor operation at off-design voltages pairs each service with a motor rating about 4% lower:

Older motors may read 220V, or 220/440, as Baldor's Edward Cowern notes in Power Transmission Engineering. Phoenix Phase Converters' 240V to 3 phase sizing page says a 240V 3 phase nameplate is sometimes written as 230V or 220V. A plate with two voltages, like 220/440 or 230/460, means the motor can be connected for either one. In a 240V shop, a licensed electrician wires the motor for its 220V or 230V side.

Will a 230V motor run on 208V?

A motor rated only for 230V can run on 208V 3 phase, but it loses torque and runs hotter. NEMA, the motor makers' standards group, cautions against running a 230V motor on a 208V system, according to HPAC Engineering.

The DOE tip sheet says motors are designed to run within 10% of their nameplate voltage. 208V is 9.6% below 230V, just inside that limit. Some voltage is lost in the wire on the way to the motor. DOE's table pairs 208V service with a 200V motor rating. That 200V is the voltage DOE expects to reach the motor. 200V is 13% below 230V, past the 10% limit.

DOE says torque falls with the square of the voltage. For a 230V motor getting 200V, that's (200 ÷ 230) x (200 ÷ 230) = 0.76, or about 24% less starting and running torque. To carry the same load, the motor draws more current. DOE's table shows full load current up 5 to 10% at 90% of nameplate voltage. A 230V motor getting 200V is further down, at 87% of its rating (200 ÷ 230). The sheet warns of "possible overheating at rated load conditions," meaning when the motor works at its full rated load.

Heaters lose power on 208V too. If your shop is on 208V power, a heating element rated for 240V makes about 75% of its rated power. HyperPhysics, a physics reference by Rod Nave hosted at Georgia State University, explains that power follows the square of the voltage: (208 ÷ 240) x (208 ÷ 240) = 0.75. On a 4,500W heater, that's 4,500 x 0.75 = 3,375W.

How to tell if a motor is rated for 208V

Look for one of these on the nameplate:

• A 200V rating. This is the motor DOE pairs with 208V service. ABB's white paper on federal motor efficiency rules (WP11) recommends a 200V motor for 208V operation.
• 208 in the voltage line, as in 208-230/460. The motor is rated for 208V, 230V or 460V. Basso writes that it "will have degraded performance at 208 V." DOE adds that these motors run hotter at 208V than at 230V.
• A full load amps figure at 208V. ABB's guide to reading a NEMA motor nameplate says: "If the current value is supplied, it means the motor can run at 208 V without overheating."
• "Usable on 208 Volts" on an older plate. The DOE sheet says some 230/460V motors carry it. NEMA says new nameplates dropped the marking after DOE changed its motor efficiency testing rules in April 2023. On a newer motor, look for 208 in the voltage line or the 208V amps figure instead.

If the plate shows none of these, treat it as a 230V-only motor and ask the motor maker before you run it on 208V.

What voltage does a phase converter or VFD put out?

A phase converter or VFD on single phase power puts out 3 phase at about the voltage it takes in, unless the maker builds it to do otherwise. Phoenix Phase Converters' article on running 480V equipment from 240V says: "On its own, a rotary phase converter produces a three-phase voltage that matches the input voltage."

VFDs with single phase input follow the same pattern by default. Hitachi's WJ-C1 brochure lists its models for 200V to 240V single phase power with 3 phase output of 200 to 240V. The brochure adds that the drive "cannot output the voltage more than the input voltage." Some drives are built to raise the voltage. Invertek's spec page lists 110V input Optidrive E3 models with 230V 3 phase output.

A motor rated only for 460V or 480V fits neither row. The next section covers it. Our guide to rotary vs digital phase converters vs VFDs compares the three types.

Can you run a 480V 3 phase machine in a 240V shop?

A 480V 3 phase machine can run in a 240V shop if the machine is built for both voltages. Phoenix Phase Converters' 240V to 3 phase sizing page says dual voltage 240V/480V machines need only a change in internal wiring. A licensed electrician makes that change. A motor plate that lists two voltages, such as 230/460V, covers only the motor. Other parts of the machine may be built for one voltage. Check the machine's documentation or ask the machine maker. A machine rated only for 460V or 480V needs a setup planned by the converter maker's engineers.

DOE's tip sheet explains that a dual voltage motor's leads are connected one way for the lower voltage and another way for the higher one, inside the motor's terminal box. A licensed electrician moves them. Baldor-Reliance's motor manual (MN408) says to connect the leads as shown on the diagram on the nameplate or inside the box cover.

For a 480V-only machine, Phoenix's article on running 480V equipment on 240V single phase recommends a rotary phase converter plus a step-up transformer. The transformer raises the voltage. It can't make 3 phase by itself. Hammond Power Solutions says: "Transformers cannot convert a single-phase source to a three-phase source." Our guide on whether a transformer can make 3 phase from single phase explains why.

How do you find out which voltage your shop has?

Call your utility and ask which service feeds your building, by name: 120/240V single phase, 120/208V wye, 240V delta, 120/240V delta, 277/480V wye or 480V delta. To confirm it at the panel, have a licensed electrician check it. One reading can mislead: 240V between two wires shows up on household single phase and on 240V delta.

Then compare your service with the voltage line on the machine's nameplate. Before you buy a used machine, ask the seller for a photo of the plate. Our post on single phase vs 3 phase power for a home shop walks through both checks: reading the machine's nameplate and finding out which service your building has.

What to do next

1. Write down the horsepower, volts, full load amps and phase from the nameplate.
2. Match the volts to your shop's power with the tables above.
3. Enter the motor's horsepower, full load amps or kW, plus the voltage, into our phase converter sizing calculator. It shows each maker's own sizing rule and the math.
4. Read our guide to running 3 phase machines on single phase power for the rest of the setup.

If you'd rather talk it through, call us at (855) 923-2610 with the nameplate in front of you, or send a note through our contact page.