Locked Rotor Code
Reference data and engineering information about locked rotor code for electrical applications.
lockedrotorcode
Overview
Engineering reference data for Locked Rotor Code in electrical engineering.
Key Formulas
Ohm's Law
Voltage = Current × Resistance.
Power
Electrical power.
Energy
Energy = Power × Time.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Voltage | V | |
| Current | A | |
| Resistance | Ω | |
| Power | W |
NEMA Locked Rotor Code Classification
The National Electrical Manufacturer's Association (NEMA) classifies motors by their locked rotor kVA per horsepower ratio using design code letters.
19 rows
NEMA Code Letter | kVA/HP with locked rotor(kVA/HP) | Approximate Mid-Range Value(kVA/HP) |
|---|---|---|
| A | 0 - 3.14 | 1.6 |
| B | 3.15 - 3.55 | 3.3 |
| C | 3.55 - 3.99 | 3.8 |
| D | 4.0 - 4.49 | 4.3 |
| E | 4.5 - 4.99 | 4.7 |
| F | 5.0 - 5.59 | 5.3 |
| G | 5.6 - 6.29 | 5.9 |
| H | 6.3 - 7.09 | 6.7 |
| J | 7.1 - 7.99 | 7.5 |
| K | 8.0 - 8.99 | 8.5 |
| L | 9.0 - 9.99 | 9.5 |
| M | 10.0 - 11.19 | 10.6 |
| N | 11.2 - 12.49 | 11.8 |
| P | 12.5 - 13.99 | 13.2 |
| R | 14.0 - 15.99 | 15 |
| S | 16.0 - 17.99 | 17 |
| T | 18.0 - 19.99 | 19 |
| U | 20.0 - 22.39 | 21.2 |
| V | 22.4 - & up | 22.4 |
Source: engineeringtoolbox.com
Standard 3-Phase Motor Locked Rotor Codes
The following are common NEMA locked rotor code letters for standard 3-phase motors based on horsepower rating.
| Motor Horsepower | Typical Locked Rotor Code | kVA/HP Range |
|---|---|---|
| Less than 1 hp | L | 9.0 - 9.99 |
| 1.5 to 2 hp | L or M | 9.0 - 11.19 |
| 3 hp | K | 8.0 - 8.99 |
| 5 hp | J | 7.1 - 7.99 |
| 7.5 to 10 hp | H | 6.3 - 7.09 |
| More than 15 hp | G | 5.6 - 6.29 |
Key Observation: In general, smaller motors require a higher starting kVA per horsepower than larger motors. The locked rotor kVA is typically determined from the motor nameplate or manufacturer specifications.