How to Convert Single-Phase Current to Three-Phase

By David Brown, eHow Contributor

 
 
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If your utility doesn't provide three-phase power, you can convert single-phase yourself.

Many large industrial motors run on three-phase power; in fact, nearly all electric motors rated at over five horsepower require three-phase current. Phase converters convert common single-phase power into three-phase.



There are three types of phase converter: static, rotary and solid state. Static converters are simple and inexpensive but are rather inefficient. Three-phase motors powered by a static converter should be used at no more than one-half their rated load, and only intermittently.



Rotary phase converters are also relatively simple and inexpensive, yet are somewhat more efficient than static phase converters. Still, motors powered by a rotary phase converter must be run at less than their factory-rated power output. Rotary phase converters are generally rated for continuous duty.



Solid-state phase converters are more expensive than static or rotary converters, but their increased efficiency makes solid-state converters a better investment over time. Motors powered by a solid-state phase converter are typically de-rated by about five percent and can run continuously.

Things You'll Need

• Phase converter
• Single phase, 220 to 240 volt AC power
• Wire stripper

Instructions

1. • 1
     Turn off the main breaker at the breaker panel. If the panel lacks a main breaker, you can remove the electrical meter from its socket to cut off all power to the panel.
   • 2
     Remove the cover from the breaker panel, and install the new double-pole breaker by snapping it in place in an open slot. The new breaker will connect to the two "hot" single-phase buss bars in the panel and supply 240 volt single-phase current to the phase converter.
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   • 3
     Wire the phase converter to the newly installed circuit breaker. The two “hot” leads (red and black) are interchangeable and are connected to the screw terminals on the circuit breaker. The white “neutral” wire is connected to the neutral buss bar inside the panel, and the green ground wire is connected to the ground buss bar. You can identify the ground buss bar by the bare copper wires attached to it, and the neutral buss bar by the white wires connected to it. Note that some phase converters don't have neutral (white) wire.
   • 4
     Remove the knockout corresponding to the new breaker in the panel cover and reinstall the cover.
   • 5
     Wire the three-phase load to the load side of the phase converter. The exact connections will vary with the brand of phase converter, but the load side should be clearly labeled.
   • 6
     Turn on the main breaker, and the newly installed breaker, and test the phase converter for proper operation. Start the motor and check that it quickly comes up to speed; it should attain full operating speed in 15 seconds or less. Note that a volt meter may give erroneous readings when testing a phase converter without a load.

Tips & Warnings

• If you have large motors, or many motors needing three-phase current, check with the local electrical utility to see if three-phase power is available at your location. You’ll save money by having the utility supply three-phase current rather than converting single-phase to three-phase.
• Electric motor rebuilders can often convert smaller three-phase motors to run on single-phase current, eliminating the need for a phase converter.
• Use extreme caution when working with electricity.