Small Motor Control (1/4 HP - 200 HP)
Thomas Mason, P.E.
This two hour
online course discusses methods of motor control and representation in motor
design. It is directed towards small AC induction motors in the range of 1/4
HP to 200 HP. It is important to understand these principles because automatic
control technology has been advancing so rapidly that basic safety and simple
manual functions may be overlooked. This course will enable the supervising
engineer or submittals approval officer to recognize safety and functional design
This course includes a multiple-choice quiz at the end.
At the conclusion of this course, the student will:
Small AC induction
motors (1/4 HP to 200 HP) are simple and reliable. They are almost always started
by connecting power to the terminals. If a plug is inserted into a receptacle
to start a motor, a substantial electrical arc is produced by the inrush current.
For this reason, a switch or magnetic relay contact is used, which shields the
arc from the operator. As motors increase in size from fractional horsepower,
it becomes economic to provide motor protection, so that the motor can be stopped
and repaired before catastrophic failure. As motor control becomes more complicated,
standard designs must be followed to assure operator and maintenance safety
and to comply with government regulations. OSHA and local building Codes require
compliance with NEC 70, the National Electric Code. Beyond this minimum, NFPA
79, Electrical Standard for Industrial Machinery, is required for certain controls
but is an excellent guide for all controls.
The course content is in a PDF file (89 KB) Small_Motor_Control.pdf. You need to open or download this document to study this course.
Motors in the range
¼ - 200 HP are almost universally controlled by motor starters. The majority
of the presently installed motor starters utilize electro-mechanical components.
This course demonstrates graphic representation of simple controls and discusses
the trend towards solid-state controls. A brief discussion of testing for response
to open circuits and short circuits is included.
For additional technical information related to this subject, please visit the following websites or web pages:
NFPA 79 - Electrical Standard for Industrial Machinery
General Electric : Products & Solutions : Business Products AZ
Cutler-Hammer Home Page
Square D Motor
Square D - Electrical Distribution, Control and Power Management
Siemens Motor Control
Siemens Distribution Equipment SPEEDFAX 1999
Motor Contactors - Automationdirect.com
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.