Core question: How do I determine the right size phase converter for my equipment?

In this guide

  1. Step 1: Identify Your Equipment
  2. Step 2: Calculate Your Load Profile
  3. Step 3: Apply Safety Margins
  4. Common Sizing Scenarios

Step 1: Identify Your Equipment

List every piece of three-phase equipment in your facility. For each machine, record: equipment type and manufacturer, horsepower (HP) rating, Full Load Amps (FLA) or Service Factor Amps (SFA) from the nameplate, voltage requirement (240V or 480V), and whether it runs continuously or intermittently. The nameplate is typically a metal plate riveted to the motor housing. If the nameplate is missing or illegible, the manufacturer can provide specifications from the model/serial number.

Step 2: Calculate Your Load Profile

Determine which equipment runs simultaneously. Your converter must handle the peak simultaneous load — not the sum of all equipment. Example: if you have a 5 HP lathe, 3 HP mill, 7.5 HP compressor, and 2 HP dust collector, but never run the lathe and compressor at the same time, your peak simultaneous load is 7.5 + 3 + 2 = 12.5 HP (compressor + mill + dust collector). However, if there's any chance you'll run both, include both: 7.5 + 5 + 2 = 14.5 HP.

Step 3: Apply Safety Margins

Add 20–25% above your calculated peak load for standard motor applications. Add 25–50% for CNC machines and equipment with high inrush current. This margin covers startup surges (motors draw 5–7x their running current at startup), power factor variations between different load types, and future equipment additions. It's always better to have a converter that's slightly oversized than one that's undersized — an oversized converter simply idles at a lower percentage of its capacity.

Key takeaway: Always over-size your phase converter by at least 20% to handle startup surges and future equipment additions. For CNC machines, go 25–50% above rated HP.

Common Sizing Scenarios

These scenarios are common starting points — the actual load profile determines the exact size needed:

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