After 50+ years in the phase converter business, the most common question we get is simple: "What size do I need?" This page gives you the quick answer for your specific equipment — then explains why.
The short answer:
For most equipment, your phase converter should be 2× the HP of your largest motor. For piston compressors, use 2.5×. For dust collectors and large fans, use 3×. Use the chart below for specific equipment recommendations, or call us at (800) 417-6568 for free sizing help.
Want to understand the methodology? See our complete Phase Converter Sizing Guide for step-by-step instructions and the reasoning behind the 2×, 2.5×, and 3× rules.
What Determines the Right Size?
Three factors determine the correct phase converter size for your application:
- Your largest single motor — the converter must match or exceed its starting current. This is the biggest driver.
- Simultaneous loads — how many motors run at the same time during normal operation?
- Starting characteristics — some equipment (compressors, dust collectors, loaded equipment) draws much more current at startup than running.
Quick Sizing Formula
Converter HP ≥ (Largest Motor HP × Multiplier) + Other Running Motors
Where multiplier is:
- 2× for standard motor loads (mills, lathes, saws, fans, screw compressors)
- 2.5× for piston compressors, CNC with heavy rapids, loaded starts
- 3× for dust collectors, large fans, high-inertia impellers
Example: 20 HP CNC mill (main) + 5 HP dust collector + 3 HP compressor running together:
Recommended: DualZone 60 HP or GP75PL
Sizing Chart by Equipment Type
Use this chart as a starting point. Always verify with your equipment's actual nameplate data before ordering.
| Equipment | Typical HP | Recommended | Notes |
|---|---|---|---|
| CNC Machining | |||
| Small CNC Mill (Haas Mini, Tormach) | 5–10 HP | GP10NL | Standard 2× rule |
| Mid CNC (Haas VF-2/3, Fadal) | 15–20 HP | GP20NL to GP25PL | Consider PL series for heavy rapids |
| Large CNC (Haas VF-6+, DMG Mori) | 25–40 HP | GP50NL / GP60NL | 2.5× for production environments |
| Engine Lathe (14–18") | 3–7.5 HP | GP7.5PL to GP15PL | Standard 2× rule |
| Bridgeport / Knee Mill | 1–3 HP | GP5PL / GP7.5PL | Standard 2× rule |
| Compressors (Hard-Starting) | |||
| Air Compressor (piston) | 5–25 HP | 2.5× rule — see below | 10 HP comp → GP25PL minimum |
| Air Compressor (rotary screw) | 10–50 HP | 2× rule (unloaded start) | Start relief valve allows 2× rule |
| HVAC Scroll Compressor | 3–15 HP | DualZone series | Best for scroll's hard-start profile |
| Refrigeration Compressor | 5–20 HP | 2.5× rule, NLA series | NLA for continuous duty |
| Woodworking | |||
| Table Saw (SawStop, Powermatic) | 3–7.5 HP | GP7NL / GP10NL | 2× rule |
| Dust Collector (Industrial) | 3–10 HP | 3× rule — critical | 5 HP DC → GP15PL minimum |
| Wide Belt Sander | 15–25 HP | GP30PL to GP50NL | 2× rule; heavy starting torque |
| Planer / Moulder | 10–20 HP | GP20NL to GP40NL | Standard 2× rule |
| Full Woodworking Shop (multi-machine) | 15–30 HP total | GP30NL to GP50NL | Account for dust collector at 3× |
| Agriculture & Irrigation | |||
| Irrigation Pump (centrifugal) | 5–50 HP | AutoStart series, 2.5× | AutoStart for automatic on/off |
| Deep Well Pump (submersible) | 5–30 HP | DualZone, 2.5× | Starts against water column |
| Grain Dryer (fan motor) | 15–75 HP | GP30NL to GP150 | 2.5× for loaded starts |
| Silo / Feed Mill Auger | 3–10 HP | GP10NL / GP15NL | 2× rule |
| Welding & Fabrication | |||
| MIG/TIG Welder (3-phase) | 10–25 HP equiv | GP15NL to GP30NL | Size for peak, not average |
| Plasma Cutter (CNC) | 10–20 HP | GP20NL to GP40NL | 2× plus CNC control load |
| Spot Welder (Pro Spot i4S) | 22V equiv | DualZone | Specific guide |
| Other Industrial | |||
| Elevator / Lift | 10–40 HP | GP25PL to GP100 | 2.5× — always loaded starts |
| Hydraulic Press | 5–30 HP | GP15PL to GP75NL | 2.5× for loaded starts |
| Surface Grinder | 2–5 HP | GP5NL to GP10NL | Standard 2× rule |
Don't see your equipment? Call us at (800) 417-6568 — we've sized converters for everything from dental labs to oil rigs.
Choosing the Right Series: NL vs PL vs NLA
Once you have the HP, you need to pick the right product series:
| Series | Best For | Features |
|---|---|---|
| NL (Standard) | Single large machine at a time | Reliable, simple, lifetime warranty. Most popular. |
| PL (Premium) | Multiple motors simultaneously | Better voltage balance under multi-load. Full machine shops, HVAC, production. |
| NLA (Compressor Duty) | Hard-starting, high-inrush loads | Engineered for compressors, pumps, elevators, high-inertia fans. |
| DualZone | Mixed HP ranges, HVAC scroll compressors, deep well pumps | Patented two-winding design; handles widest load range. |
Not sure? Call us. We'll tell you honestly which one you need. We'd rather sell you the right converter than upsell you on features you don't need.
460V Equipment? You Need a Transformer Package
If your equipment runs on 460V or 480V three-phase but your service is 230V single-phase, you need a converter plus a step-up transformer. We sell these as integrated packages:
- NLT Series — Standard NL converter + 230V→460V transformer in one package
- NLTA Series — NLT plus AutoLink for compressor-duty applications
- NH Series — For facilities with 460V single-phase service going to 460V three-phase
Still Not Sure? We'll Size It For Free
Send us your equipment nameplate (snap a photo and text it to us) and we'll tell you exactly what you need. No charge, no obligation, no sales pressure.
Monday–Friday, 7 AM–5 PM MST
⚡ Use the Sizing Wizard Browse Phase Converters
Phoenix Phase Converters — Made in the USA since 1968 • Lifetime warranty
Related Resources
- Complete Phase Converter Sizing Guide — The full methodology with examples
- Phoenix Knowledge Hub — Sizing & Selection — In-depth technical resources
- Three-Phase Motor Wiring Diagrams — Wire your converter correctly
- How Phase Converters Work — Understand the technology