Single-Phase Rural Distribution Service for Motors and Phase Converters
|Publication Date:||1 April 2013|
This Engineering Practice concerns 3.7 kW (5 hp) and larger single-phase motors, and three-phase motors with phase converters, that are started infrequently (generally with less than 6 starts in a 24-hour period and not more than 1 start between 6 p.m. and midnight) and that serve loads with non-pulsating power requirements. Some examples are motors for fans on crop dryers, feed grinders, silo unloaders, irrigation pumps, and auger feeders.
This Engineering Practice is intended to apply to Single-Phase Rural Distribution Lines with a phase-toneutral voltage of at least 7200 volts and constructed after the adoption of this Engineering Practice in December 1969. Many power suppliers impose lower limits on lines of lower voltage or older construction.
Excluded from this Engineering Practice are those motors used on pulsating loads and loads started frequently. Typical examples are motors on some deep-well piston pumps, reciprocating compressors, rock crushers, stamping machines, automatically controlled water pumps, and refrigeration systems.
This Engineering Practice is intended to serve the following purposes:
To provide minimum utility service regulations for motors on single-phase rural distribution systems in order that rural consumers, equipment manufacturers, and others concerned will know the single-phase motor sizes and types that will be served in areas where three-phase power is not available.
To eliminate confusion in motor applications where motor load is well above nameplate rating because of service regulations based on rated horsepower of the motor.
To call to the attention of power suppliers the need by farmers for larger motor-operated equipment and to encourage the use of such equipment.
To encourage uniform criteria of maximum starting current and minimum voltage to enable equipment and motor manufacturers to design and produce satisfactory electric motor-operated equipment for present-day farms.
To encourage the use of magnetic motor controllers for 3.7 kW (5 hp) and larger motors.