Phase Converter FAQ

A phase converter is an electrical device that converts single-phase power (the standard residential supply with two lines: live and neutral) into three-phase power (three live lines providing smooth, efficient energy transmission). You need one when your equipment — such as CNC machines, industrial compressors, mills, lathes, or welding systems — requires three-phase power, but your facility only has single-phase utility service. Rather than paying $10,000–$50,000+ to have the utility company run three-phase lines to your location, a phase converter delivers the same quality power at a fraction of the cost. Phoenix Phase Converters manufactures heavy-duty rotary phase converters built to industrial standards, backed by American manufacturing and a lifetime warranty.

A rotary phase converter uses an idler motor to generate continuous, balanced three-phase power — producing true three-phase output at all times. The rotating mass acts as a flywheel, smoothing voltage fluctuations and delivering utility-grade power quality. A static phase converter uses capacitors to provide a starting boost for motors — it only assists with motor startup. Once the motor reaches operating speed, the converter drops out, leaving the motor running on single-phase at approximately 2/3 of rated capacity. Static converters cannot run CNC machines, sensitive electronics, or multiple machines simultaneously. Rotary converters can run your entire shop from a single unit. For 90% of applications, a rotary phase converter from Phoenix is the correct choice.

Digital phase converters use solid-state electronics to generate three-phase power with extremely tight voltage balance (±1–2%). They're quieter and consume less standby power. However, they cost 2–3x more than rotary converters (typically $2,500–$15,000+ depending on capacity), are sized to specific loads rather than flexible shop-wide use, and have complex electronics that can be expensive to repair. Rotary phase converters deliver excellent balanced power at a significantly lower cost, can flexibly handle varying loads across multiple machines, and use proven technology that has been reliable for 40+ years. Many rotary converters installed in the 1980s are still running today. For most shops, farms, and factories, a rotary phase converter provides the best balance of power quality, versatility, and value.

To properly size a phase converter: (1) Identify all equipment you'll run simultaneously. (2) Find the Full Load Amp (FLA) or Service Factor Amp (SFA) rating on each motor's nameplate. (3) Add up the total amp draw of equipment running at the same time. (4) Select a phase converter rated above that total. General rules: size for the largest single motor that needs to start plus all concurrent loads. A 10 HP rotary converter typically handles a 10 HP main load, while a 15 HP converter provides headroom for startup surges and multiple machines. Over-sizing by 20–25% is recommended for shops that plan to add equipment. Phoenix Phase Converters offers free sizing assistance — call 1 (866) 418-9060 and a dedicated support agent will help match the right converter to your exact application.

Yes — this is one of the primary advantages of a rotary phase converter over static or digital options. A properly sized rotary converter can power your entire shop from a single unit. The key is ensuring the converter's rated output exceeds the total simultaneous amp draw of all connected equipment. For example, if you run a 5 HP lathe, a 3 HP mill, and a 2 HP compressor at the same time, you'd need a converter rated for at least 10 HP total. Phoenix Phase Converters recommends sizing 20–25% above your calculated total to handle startup surges and future equipment additions. Static converters cannot run multiple machines. Digital converters can, but are typically sized for specific loads and cost significantly more.

Yes — but only with a rotary or digital phase converter, never a static converter. CNC machines have sensitive electronic controls (servo drives, spindle drives, PLCs) that require balanced three-phase power. Voltage imbalance over 3–5% can cause erratic axis movement, poor surface finishes, control faults, and damage to control boards. Size the converter 25–50% above the CNC machine's rated HP to handle variable cutting loads.

A phase converter does not change voltage — the output voltage matches the input voltage. If your single-phase service is 240V, the three-phase output is 240V. To run 480V equipment from 240V single-phase input, you install a step-up transformer after the rotary converter (or buy a converter/transformer package). Phoenix Phase Converters sells matched converter-transformer packages for 240V-in / 480V-out applications.

Delta-configured power uses four wires: three hot lines (L1, L2, L3) and a ground. Wye-configured power uses five wires: three hots, a neutral, and a ground. Phase converters produce delta output. If your equipment requires wye (common for some HVAC and low-voltage control circuits), install a delta-to-wye transformer downstream of the converter. Be aware of the 'high leg' in delta — one leg reads ~208V to ground and must never be connected to 120V loads.

Yes, but proper setup is critical. You must install a delay timer (20–30 seconds) before power is transferred to the converter — this lets the generator's voltage and frequency stabilize. Without the delay, the transition can cause PLL faults or voltage-transient damage. Size the generator at 2–3x the converter's running load to handle startup surges. Automatic transfer switches (ATS) must be programmed with an appropriate time delay.

A rotary phase converter typically costs $1,500–$8,000 depending on horsepower rating, compared to $10,000–$50,000+ for utility three-phase installation (trenching, new transformers, and service upgrades). Utility installations can take months of permitting and construction. A phase converter ships in days and installs in a single afternoon. For remote rural locations, the savings versus utility extension can exceed $40,000.

Three-phase welding equipment — MIG, TIG, stick, submerged-arc — runs well on a rotary phase converter. Welders are highly inductive with large, variable loads; the rotary converter's flywheel effect handles the rapid load changes. Size for the welder's maximum input amperage, not its welding output. A 300-amp MIG welder may only draw 30–50 amps at 240V three-phase input. Shops with multiple simultaneous welders need a converter sized for the combined draw.