Phase Converters & Power Factor
Phase Converter Efficiency
Installing a Phase Converter
Rotary Phase Converters
Static Phase Converters
VFDs as Phase Converters
     • Harmonic Distortion
Three-Phase Motors
Phase Converters & Voltage Balance
Phase Converter Applications
     • Submersible Pumps
     • Woodworking Equipment
     • Dual Lift Stations
     • Phase Converters & Welders
     • Phase Converters & CNC Machines
     • Phase Converters & Air Compressors
     • Phase Converters & Elevators
     • Phase Converters & Wire EDM
     • Phase Converters & HVAC
Phase Converters & Transformers
     • Step-up Transformers
     • Buck-Boost Transformers
     • Isolation Transformers
Phase Converter Experts
Digital Phase Converters
Regenerative Power
Three-Phase Power
     • Delta vs. Wye Configured Power
Motor Starting Currents

Phase Converters and Isolation Transformers


An isolation transformer is commonly used to convert delta configured three-phase power to wye-configured three-phase power. Click here to learn more about the delta vs. wye configured power.

Isolation Transformers and Phase Converters

A phase converter generates a third voltage that is added to single-phase power. Single-phase power is comprised of two legs with 240V potential between them with ground and neutral halfway between. Thus, the voltage between L1 and L2 will be 240V, while the voltage to either leg and neutral/ground will be half that or 120V. The third voltage generated by the phase converter results in a triangle or delta of three voltages all 240V apart. However, the ground and neutral are still halfway between L1and L2. If you measure from the new third leg to ground/neutral, the voltage will not be 120V, but rather 208V. This is why phase converters are known to have a “high leg”.

As long as the three-phase load only derives voltages phase-to-phase, the location of ground/neutral is irrelevant.  However, if the three-phase equipment has internal 120V circuits that are powered by a phase-to-neutral connection, making this connection between the generated third leg and neutral would result in a damaging high voltage.

For three-phase equipment that requires a neutral wire connection, the three-phase power must be converted from a delta configuration to a wye configuration.  This is accomplished with a 240 V delta to 120/208V wye isolation transformer.  This assures that any of the three phase to neutral voltages will be 120V. Wye power is illustrated in figure 2.

Sizing Transformers

Transformers need to be sized to the load they will supply and usually rated in KVA, which is an acronym for “thousand volt amps”. For single-phase loads, multiply the operating voltage of the load by the amps then divide by 1,000 to get the KVA. e.g.  240V x 30A / 1,000 = 7.2 KVA.

For three-phase loads, multiply the operating voltage of the load by the amps, multiply by 1.73 (square root of three) then divide by 1,000 to get the KVA. e.g.  240V x 30A x 1.73 / 1,000 = 12.46 KVA.

Be sure to consult a knowledgeable supplier of transformers when choosing one for your application.