NEMA Motor Standards
Many motors are manufactured according to standards set by the National Electrical Manufactures Association (NEMA). A standard motor made by one manufacturer can be replaced by the same standard motor made by another manufacturer. The motor ratings, operating characteristics, and mechanical construction and dimensions are identical for all motors manufactured according to NEMA standards. Standard motors are identified by frame number. All motors identified by the Frame Number will have same physical dimensions. These standards are part of technical motor information Buna provides.
There are two general classifications of motor enclosures – the open motor and totally enclosed motor.
Open motors have openings to allow air to pass through and cool the windings. The openings are usually located in the end plates.
Open motors are further classified into the following categories.
- Semi-guarded or guarded
- Open pipe-ventilated
- Open pipe-ventilated
Totally enclosed motors are enclosed tightly enough to prevent air from entering the enclosing. However, the motors are not sealed tightly enough to be considered “airtight.” The classifications are important technical motor information. They include:
- Totally enclosed non-ventilated
- Totally enclosed fan-cooled
- Dust ignition-proof
- Totally enclosed pipe-ventilated
- Totally enclosed water-cooled
A typical motor nameplate has following information:
- NEMA Designation: Indicates the torque and current characteristics.
- Phase: Indicates the kind of power for which the motor is designed.
- Hertz: Indicates the frequency of the A/C power required to run the motor properly.
- Serial: Manufacturers code number.
- RPM: Speed of the motor at rated power. This is basic technical motor information.
- Frame: Size defined by NEMA.
- Time Hours: How long the motor may be operated at one time without overheating.
- Insulation Class: The class of insulation used in motors.
- KVA Code: Locked-rotor power input (measured in kilowatts) per horsepower of rated output.
- Model: NEMA letter code.
- Catalog number: Used by the manufacturer or user to identify the motor.
- Motor Style: Number is the manufacturer’s specification.
- Amps: Normal current drawn at the motor’s rated load, potential difference and frequency.
- Volts: Potential difference of the power supply for the motor.
- Ambient Temperature: The temperature immediate location of the motor.
- Service Factor: How much the motor may be overloaded when operating at its rated potential difference and frequency.
- Horsepower: The amount of power the motor can produce at its rated speed. This is basic technical motor information.
Standardized NEMA color code for identifying leads for a single-phase motors
T1 – Blue
T2 – White
T3 – Orange
T4 – Yellow
T5 – Black
T8 – Red
P1 – No color assigned
P2 – Brown