Single Phase to Three Phase Converter Calculator

The single-phase to three-phase converter calculator determines the required converter rating and supply current for operating three-phase equipment from a single-phase power supply. This situation arises when three-phase motors or equipment must operate in locations where only single-phase service is available — rural farms, residential shops, remote industrial sites, and small commercial buildings without three-phase utility service.

Phase converters come in two principal types. Rotary phase converters use a motor-generator set to produce a true three-phase output from single-phase input, providing good voltage balance and capable of starting large motors. Static phase converters use capacitors to generate a phase-shifted third leg, producing an unbalanced three-phase output — acceptable for some motor loads at reduced efficiency but not suitable for precision equipment or CNC machinery.

A key consideration in sizing phase converters is that the single-phase input current is always higher than what would be expected from a balanced three-phase source. On a single-phase supply, the full three-phase load power must be delivered through two conductors instead of three. For a balanced three-phase load of P watts, single-phase input power = P / η (where η is converter efficiency). The single-phase current = P / (η × V_1ph × PF).

Converter sizing follows this rule: the converter kVA rating must exceed the load kVA divided by the converter efficiency, multiplied by a safety factor (typically 2× for rotary converters, to account for starting current). As a practical guideline, size the rotary phase converter at twice the HP of the largest single motor, or at the total connected three-phase HP, whichever is larger.

The output three-phase voltage of a converter should match the motor's nameplate voltage. Most converters produce 240V three-phase from a 240V single-phase input, or 480V three-phase from a 240/480V single-phase supply (with step-up transformer). Voltage imbalance in the three-phase output (common in static converters, up to 10-15%) causes motors to run hotter and with reduced efficiency.

This calculator provides three-phase load current, minimum converter rating, single-phase supply current, and input kVA — all essential for sizing the converter, supply conductors, disconnect, and overcurrent protection for a phase converter installation.