A NEMA motor nameplate has some supplementary information. The most important ones are: a letter code, a design letter and a service factor.
Letter Code
A letter code defines the locked rotor current kVA on a per horsepower basis. The letter code consists of letters from A to V. The farther away from the letter code A, the higher the inrush current per horsepower. Below are values
of locked rotor current KVA per horse power for NEMA motors with letter code A to V:
Design Letter Code
Design letter covers the characteristics of torque and current of the motor. Design letter (A, B, C or D) defines the different categories. Most motors are design A or B motors. See NEMA Three Phase Motor Designs for more details:
Letter Code
A letter code defines the locked rotor current kVA on a per horsepower basis. The letter code consists of letters from A to V. The farther away from the letter code A, the higher the inrush current per horsepower. Below are values
of locked rotor current KVA per horse power for NEMA motors with letter code A to V:
| NEMA Code Letter | Locked Rotor KVA/HP |
|---|---|
| A | 0 - 3.15 |
| B | 3.15 - 3.55 |
| C | 3.55 - 4.0 |
| D | 4.0 - 4.5 |
| E | 4.5 - 5.0 |
| F | 5.0 - 5.6 |
| G | 5.6 - 6.3 |
| H | 6.3 - 7.1 |
| I | not used |
| J | 7.1 - 8.0 |
| K | 8.0 - 9.0 |
| L | 9.0 - 10.0 |
| M | 10.0 - 11.2 |
| N | 11.2 - 12.5 |
| O | not used |
| P | 12.5 - 14.0 |
| Q | not used |
| R | 14.0 - 16.0 |
| S | 16.0 - 18.0 |
| T | 18.0 - 20.0 |
| U | 20.0 - 22.4 |
| V | 22.4 and up |
Design Letter Code
Design letter covers the characteristics of torque and current of the motor. Design letter (A, B, C or D) defines the different categories. Most motors are design A or B motors. See NEMA Three Phase Motor Designs for more details:
Service Factor
A motor designed to operate at its nameplate power rating has a service factor of 1.0. This means that the motor can operate at 100% of its rated power. Some applications require a motor that can exceed the rated power. In these cases, a motor with a service factor of 1.15 can be applied to the rated power. A 1.15 service factor motor can be operated at 15% higher than the motor’s nameplate power. See Basic of AC Motor Service Factor Rating for more explanation