How Much Power Does a Phase Converter Draw?
A rotary phase converter draws power proportional to the load connected to it — not a fixed amount. Think of it like a transformer: it passes through whatever current your equipment demands.
Input Current Rule of Thumb
The single-phase input to your converter draws approximately 2× the three-phase full load amps (FLA) of your equipment. This is because single-phase power carries the same wattage across two legs that three-phase spreads across three.
- Example: A 10 HP three-phase motor at 230V draws ~28A three-phase FLA
- Single-phase input to the converter: ~56A
- Breaker size: 60–70A single-phase
No-Load Draw
When your equipment is off but the converter is running, the idler motor draws a small no-load current — typically 2–5% of its rated HP. A 20 HP idler draws roughly 0.5–1 HP no-load. This is minimal and costs only a few dollars per month.
Sizing Your Breaker
Always size your single-phase input breaker at 2× your equipment FLA, minimum. See our Wire Size Calculator for exact wire and breaker sizing by HP and run length.
Have more questions? Talk to an engineer.
Free sizing help — no pressure. Made in Phoenix, AZ. Lifetime warranty.
Shop Phase Converters →Related Articles
Power Draw — FAQ
Why does my single-phase breaker need to be so large?
Because single-phase carries the same wattage across two legs that three-phase spreads across three. Your single-phase input draws roughly 2x the three-phase FLA of your equipment. This is normal and expected.
Will the converter run when no equipment is connected?
Yes — the idler motor runs continuously once powered, drawing a small no-load current (2–5% of rated HP). Turn the converter off when the shop is closed to eliminate no-load draw.
Does power draw vary with load?
Yes — like a transformer, the converter draws more as connected equipment demands more. At no load, only the idler no-load current flows. At full load, input current is approximately 2x equipment FLA.
Related Articles
- How to Size a Rotary Phase Converter
- What Is a Rotary Phase Converter?
- Rotary vs Digital Phase Converters
- Phase Converter FAQ
Questions? Talk to an engineer.
Free sizing help. Made in Phoenix, AZ. Lifetime warranty on every unit.
Shop Phase Converters