The definitive motor sizing chart for US electrical installations is NEC Table 430.250 (Full-Load Currents in Amperes, Alternating-Current Motors). You use this chart to find the Full-Load Current (FLC) of a motor based on its horsepower and voltage, which then dictates the minimum wire ampacity, branch-circuit breaker size, and disconnect ratings. Do not use the motor's nameplate Full-Load Amps (FLA) for sizing the breaker or wire; the NEC table values are intentionally conservative to account for variations in motor efficiency and power factor across different manufacturers.

The Master Motor Sizing Chart (NEC Table 430.250)

How to read this table: Locate your motor's horsepower in the left column, then trace across to the column matching your supply voltage and phase configuration. The values below are derived directly from the NFPA 70 (National Electrical Code) Table 430.250. These figures assume standard AC induction motors operating at typical speeds (e.g., 1800 RPM / 4-pole). If your motor operates at a lower speed (e.g., 900 RPM / 8-pole) or is a high-torque design, the actual current draw will be higher, and you must defer to the nameplate data for overload sizing.

Table 430.250: Full-Load Current (FLC) for AC Motors (Amperes)
Motor HP 115V (1-Phase) 230V (1-Phase) 230V (3-Phase) 460V (3-Phase)
1/2 9.8 4.9 2.0 1.0
3/4 13.8 6.9 2.8 1.4
1 16.0 8.0 4.2 2.1
1.5 20.0 10.0 5.2 2.6
2 24.0 12.0 6.8 3.4
3 (Bookmark) 34.0 17.0 9.6 4.8
5 56.0 28.0 15.2 7.6
7.5 (Bookmark) 80.0 40.0 22.0 11.0
10 (Bookmark) 100.0 50.0 28.0 14.0

Derating, Column Selection, and Installation Variables

Looking up the FLC is only step one. To select the correct wire gauge, you must apply NEC ampacity rules, which depend on termination temperatures and installation environment.

Which column applies to your installation? When selecting wire from NEC Table 310.16, you must match the ampacity column to the temperature rating of your terminations, not just the wire insulation. Per NEC 110.14(C), equipment rated 100A or less is generally assumed to have 60°C terminations unless marked otherwise, while equipment over 100A defaults to 75°C. Even if you pull 90°C THHN wire, you must size the wire using the 60°C or 75°C column based on the breaker and motor starter lug ratings. For a 10 HP, 460V motor (14A FLC), NEC 430.22 requires wire sized at 125% of FLC (17.5A). Using the 75°C column, 14 AWG copper (20A) is technically sufficient, but 12 AWG is the practical jobsite standard to account for voltage drop and mechanical durability.

How derating modifies the base value: If your motor feeder runs through a hot environment or a conduit packed with other circuits, the base ampacity drops. If you have 4 to 6 current-carrying conductors in a single raceway, you must multiply the wire's base ampacity by 80% (NEC Table 310.15(C)(1)). If the ambient temperature is 113°F (45°C), you apply an additional 0.82 correction factor for 90°C THHN. A wire that looks perfectly sized on paper can overheat and melt the insulation at the motor peckerhead if you ignore these derating rows.

What the table CANNOT tell you: This chart provides Full-Load Current (FLC) for steady-state running. It does not provide Locked-Rotor Current (LRC), which can be 6 to 8 times higher during startup. Furthermore, as Fluke's motor diagnostics guide notes, the NEC table FLC is strictly for branch-circuit sizing. For sizing the internal thermal overloads inside your motor starter, you must use the exact Full-Load Amps (FLA) printed on the physical motor nameplate, typically setting the overload dial to 115% of that nameplate value.

Motor Sizing Chart FAQ

How do I size a breaker using the motor sizing chart?

Motor breakers are sized to handle massive startup inrush currents without nuisance-tripping, while still protecting the wire from short circuits. Per NEC 430.52, the maximum rating for an inverse-time circuit breaker is 250% of the motor FLC found in the chart. For example, a 5 HP, 230V 3-phase motor has a table FLC of 15.2A. Multiplying 15.2A by 2.5 gives 38A. Since 38A is not a standard breaker size (per NEC 240.6), you are permitted to round up to the next standard size, which is a 40A breaker. The 10 AWG wire (rated 30A at 60°C / 35A at 75°C) is protected from short-circuits by this 40A breaker, while the motor starter's internal overloads protect the wire from sustained, low-level overcurrents.

Why is the motor sizing chart FLC different from the nameplate FLA?

This is the most common trap for DIYers and junior electricians. The NEC Table 430.250 values represent a standardized, worst-case baseline for a given horsepower across the entire industry. The nameplate FLA is the specific, tested current draw of that exact motor model at its rated efficiency and power factor. If you use the nameplate FLA to size your breaker, you risk undersizing the branch circuit for a future motor replacement. If the original motor dies and you swap in a less efficient replacement of the same horsepower, the new motor will draw more current, potentially exceeding the wire ampacity or breaker limits you originally installed. Always use the chart for wire/breaker, and the nameplate for overloads.

Does the motor sizing chart apply to VFD or soft-start applications?

No. When a motor is driven by a Variable Frequency Drive (VFD) or a solid-state soft starter, the current profile changes fundamentally. VFDs can run motors at lower speeds where cooling fan efficiency drops, or they can push continuous torque at zero speed, causing current draws that defy standard NEC Table 430.250 assumptions. In VFD applications, the drive itself provides the motor overload protection (per NEC 430.32(A)(2)). You must size the input and output conductors based on the VFD manufacturer's specified input current rating and the motor's actual nameplate FLA, typically multiplying the VFD output current by 125% for wire sizing. The standard NEC FLC chart is bypassed for the drive-to-motor segment.