NEMA Motor Starter Sizes Chart: HP, Amps, and Selection Guide

If you are sizing a North American industrial motor controller, the direct answer lies in the NEMA ICS 2 standard. NEMA (National Electrical Manufacturers Association) motor starters are categorized into discrete sizes ranging from 00 to 9, based on maximum continuous current and horsepower ratings at specific voltages. Unlike IEC starters, which are sized to the exact application, NEMA starters are deliberately overbuilt for harsh environments, high fault currents, and millions of mechanical operations.

To use the reference table below, locate your motor's voltage and phase in the top row, then match your nameplate horsepower to the corresponding column. The leftmost column provides the NEMA Size and its maximum continuous ampacity. Bookmark this rule of thumb: Sizes 1, 2, and 3 cover roughly 80% of all commercial HVAC, pump, and conveyor applications in the 5 HP to 100 HP range.

The Complete NEMA Motor Starter Sizes Chart (ICS 2)

The following data is derived from the NEMA ICS 2-321 standard for industrial control equipment. This table assumes standard ambient temperatures (40°C / 104°F) and normal starting duty cycles.

Which Column Applies to Your Installation?

The most common mistake when reading a NEMA motor starter sizes chart is confusing single-phase and three-phase horsepower columns. The electrical physics dictate that a 10 HP motor running on 230V single-phase will draw significantly more current than a 10 HP motor running on 230V three-phase.

• 115V (1Φ) Column: Applies strictly to single-phase fractional and small integral horsepower motors (e.g., residential HVAC compressors, small shop tools). Notice the table stops listing 1Φ HP after Size 2; NEMA does not standardize single-phase starters beyond 10 HP because the starting current becomes unmanageable for standard branch circuits.
• 230V (3Φ) Column: Applies to three-phase industrial motors running on 208V/240V delta or wye systems. This is the standard for older manufacturing facilities and municipal water pumps.
• 460V (3Φ) Column: Applies to modern three-phase industrial motors running on 480V nominal systems. This is the most common voltage for heavy manufacturing, large air handlers, and industrial conveyors.

If your motor nameplate reads "208-230/460V", you must select the column that matches the actual supply voltage at the starter's line terminals, not the motor's capability. A 50 HP motor on a 460V system requires a Size 2 starter (50 HP max). If you move that exact same motor to a 230V facility, it now requires a Size 3 starter, because the current draw doubles at the lower voltage.

How Derating and Duty Cycles Modify Your Size Selection

The chart above assumes "Normal Duty"—starting a motor across-the-line, letting it accelerate to full speed, and running it continuously. Real-world jobsite conditions frequently violate these assumptions, requiring you to derate the starter (move up to the next physical size).

According to industry motor control guidelines and NEMA ICS 2, you must increase your NEMA size by one full step under the following conditions:

1. Severe Starting Duty (Jogging and Plugging): If the motor is used in a hoist, crane, or punch press where it is rapidly started, stopped, and reversed (plugging), the contacts will suffer immense thermal and mechanical stress from repeated locked-rotor currents. A 25 HP, 460V motor normally takes a Size 1 starter. For a crane application, you must install a Size 2.
2. High Ambient Temperature: NEMA ratings assume a maximum ambient temperature of 40°C (104°F) inside the enclosure. If the panel is located next to an industrial furnace or in an unventilated desert pump house where internal temperatures exceed 40°C, the thermal overload relays will trip prematurely and contact life degrades. Move up one size or install forced-air cooling on the panel.
3. High Altitude: Above 3,300 feet (1,000 meters), the thinner air reduces the dielectric strength and cooling capacity of the enclosure. NEMA requires a 10% derating for continuous current for every 3,300 feet above sea level.

What the NEMA Chart Cannot Tell You (And How to Fill the Gaps)

While the NEMA motor starter sizes chart gives you the correct physical frame and contact rating, it leaves three critical engineering variables undefined. Ignoring these will result in failed inspections or catastrophic equipment failure.

1. Short Circuit Current Rating (SCCR)

A NEMA Size 2 starter does not have an inherent SCCR on its own. The SCCR is a property of the combination of the starter and the upstream overcurrent protective device (fuse or breaker). A Size 2 starter might only withstand 5,000 Amps (5kA) of fault current if protected by a standard thermal-magnetic breaker. However, if you pair that exact same starter with the manufacturer-specified Class RK1 or Class J fuses, the SCCR jumps to 65kA or 100kA. Always verify the combination SCCR against the available fault current at your panelboard.

2. Enclosure Type (NEMA 1 vs. 12 vs. 4X)

The electrical size (00-9) is entirely separate from the environmental enclosure rating. A Size 3 starter can be housed in a NEMA 1 (indoor, dust-light) sheet metal box, or a NEMA 4X (watertight, corrosion-resistant stainless steel) enclosure for a food processing washdown area. Specify the enclosure based on the physical environment, referencing manufacturer enclosure guides to ensure proper thermal dissipation.

3. NEMA vs. IEC Philosophy

If you are sourcing parts globally, you will encounter IEC (International Electrotechnical Commission) starters. IEC starters are not standardized by rigid size numbers; they are application-specific and sized exactly to the motor's FLA. An IEC starter for a 50 HP motor will be physically smaller and cheaper than a NEMA Size 2. Choose NEMA when you need standardized replacement parts, extreme mechanical longevity, and robustness against unpredictable grid conditions. Choose IEC when panel space is at a premium and the operational duty cycle is strictly controlled.