3-Phase Circuit Breaker & Wire Size Calculator
Free online tool • 2026 NEC Compliant
Three-phase systems are standard in commercial and industrial settings. Sizing a three-phase breaker requires calculating the line current using the phase multiplier (1.732 / square root of 3). Enter your three-phase power requirements below to calculate standard overcurrent protection and wire size.
Recommended Sizing
NEC Standard SizeBreaker Type: Standard Inverse-Time
NEC Reference Note: 125% multiplier applied for continuous loads per NEC 210.20(A).
How to Use This Calculator
Enter source voltage
Select 3-phase source voltage: typically 208V, 240V, or 480V.
Enter load current or kilowatts
Provide the total balanced load current or kilowatt draw.
Apply continuous load multiplier
Multiply current by 125% if the load runs for 3 hours or more.
Round to standard size
Round up to the next standard three-pole breaker rating from NEC 240.6.
Frequently Asked Questions
How do you calculate breaker size for 3-phase?
First, find the line current: Amps = Watts / (Volts × 1.732 × Power Factor). For continuous loads, multiply the current by 125%. Finally, select the next standard size double-pole or three-pole breaker per NEC 240.6(A).
What multiplier is used for three-phase power?
A multiplier of 1.732 (the square root of 3) is applied to three-phase power calculations to account for the phase displacement between the three hot conductors.
Specific Sizing Guides & Calculators
Electric Range Circuit Breaker & Wire Size
What size breaker does an electric range need? Standard ranges require a 40 amp or 50 amp double-pole breaker on a dedicated 240V circuit per NEC requirements.
Electric Water Heater Breaker & Wire Size
What size breaker does a water heater need? Standard 4500W electric water heaters require a 30A double-pole breaker with 10 AWG copper wire per NEC rules.
Electric Dryer Breaker & Wire Size
Standard electric dryers require a 30 amp double-pole breaker with 10 AWG copper wire on a 240V circuit. Learn how to size your dryer circuit correctly per NEC.
Standard Breaker Sizes NEC & Fuse Ratings
Standard breaker sizes per NEC 240.6(A). Comprehensive chart of standard circuit breaker amperage ratings from 15A to 6000A for residential & commercial.
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