Motors & Loads calculator

NEMA Starter Sizing Calculator

This NEMA starter sizing calculator determines the correct NEMA starter size for AC induction motors based on horsepower and voltage ratings per NEMA ICS 2 (Industrial Control and Systems: Controllers, Contactors and Overload Relays). The calculator covers NEMA sizes 00 through 9, supporting both single-phase and three-phase motors at standard voltages from 115V to 600V. It provides contactor continuous ratings, breaking capacities, and overload relay sizing guidance. All selections should be verified against the motor nameplate, NEC Article 430, and manufacturer specifications before installation.

Updated June 21, 2026

Calculator Inputs

Calculation Results

Enter values above to see calculation results

Calculation history

Example Calculations

25HP Pump Motor at 480V

Select NEMA starter for a 25HP 3-phase pump motor at 480V

Inputs

Motor HP: 25
System Voltage: 480 V
Motor Phase: Three phase
Calculation Mode: Complete starter selection

5HP Compressor at 230V

Select NEMA starter for a 5HP 3-phase compressor at 230V

Inputs

Motor HP: 5
System Voltage: 230
Motor Phase: Three phase
Calculation Mode: Size from HP

How to Use

How to Size a NEMA Motor Starter

This calculator helps you select the correct NEMA starter size for your motor based on horsepower (HP) and system voltage per NEMA ICS 2 standards.

Quick Reference: NEMA Starter Sizes @ 460V 3-Phase

NEMA Size	Max HP	Continuous Amps	Breaking Capacity
00	2 HP	9 A	54 A
0	3 HP	18 A	108 A
1	7.5 HP	27 A	162 A
2	15 HP	45 A	270 A
3	30 HP	90 A	540 A
4	50 HP	135 A	810 A
5	100 HP	270 A	1620 A
6	200 HP	540 A	3240 A
7	400 HP	810 A	4860 A
8	600 HP	1215 A	7290 A
9	900 HP	2250 A	13500 A

Step 1: Select Calculation Mode

Size from Motor HP – Primary mode: enter HP and voltage to get NEMA size.
Verify Starter Rating – Confirm a NEMA size is adequate for your motor.
Contactor Ratings – Get continuous and breaking ampere ratings.
Complete Selection – Full specification with overload sizing and derating.

Step 2: Enter Motor Information

Motor Horsepower – Nameplate HP rating.
System Voltage – 208V, 230V, 460V, 480V, 575V, or 600V.
Motor Phase – Single-phase or three-phase.

Step 3: Read Results

NEMA Starter Size – Recommended size (00 through 9).
Maximum HP Rating – Full rating of selected size.
Contactor Ratings – Continuous and breaking capacities.
Overload Setting Range – 115-125% of motor FLA.

Common Applications

Industrial motor control panel design

HVAC equipment motor starter selection

Pump and compressor motor starters

Conveyor and material handling systems

Manufacturing equipment motor controls

MCC (Motor Control Center) design

Replacement starter sizing for existing motors

Frequently Asked Questions

What size NEMA starter do I need for a 10HP motor?

For a 10HP 3-phase motor at 460V/480V, you need a NEMA Size 2 starter (rated up to 15HP). At 230V, a 10HP motor also requires NEMA Size 2. For 200V/208V, NEMA Size 3 may be required as Size 2 is only rated for 7.5HP at those voltages.

What is the difference between NEMA starter sizes?

NEMA starter sizes (00, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9) define the maximum motor HP and contactor electrical ratings. Each size up approximately doubles the HP capacity and continuous ampere rating. Size 00 handles up to 2HP at 460V; Size 9 handles up to 900HP.

Can I use a larger NEMA starter than required?

Yes, using a larger NEMA starter than minimum required is acceptable and may provide additional margin for inrush current and longer life. However, the overload relay must still be sized to protect the actual motor FLA, typically set at 115-125% of nameplate current per NEC 430.32.

How do I size the overload relay for a NEMA starter?

Overload relays should be sized at 115-125% of motor nameplate full-load amps (FLA) per NEC 430.32. For a motor with a service factor of 1.15 or higher, or temperature rise of 40°C or less, the maximum is 125%. For all other motors, the maximum is 115%.

What information do I need to size a NEMA motor starter?

To properly size a NEMA motor starter, you need: (1) Motor horsepower (HP), (2) System voltage (208V, 230V, 460V, 480V, 575V, 600V), (3) Phase (single or three-phase), and (4) Motor full-load amps (FLA) from nameplate for overload relay sizing.

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