Electric Motor Control Basics - Book - Page 32
Industrial Control Basics: Part 3, Starters
There are two circuits in a motor starter, which are as follows:
1. Power Circuit: The power circuit connects the line to the motor. It provides
transmission of electricity through the starter contacts, overload relay, and then
to the motor. The motor current is carried by the power (main) contacts of the
contactor.
2. Control Circuit: This is the other motor starter circuit, which operates the
contactor to turn it on or off. The contactors main contacts are responsible for
allowing or interrupting the flow of current to the motor. To do this, the contacts
in the control circuit are either opened or closed. The control circuit energizes the
contactor coil, which creates an electromagnetic field. The power contacts are
pulled by this electromagnetic field to a closed position. This completes the circuit
between the motor and the line. This way, remote operations are made possible by
the control circuit. The control circuit can be wired in the following two ways:
Method 1: One of the most widely used methods employed for wiring the control
circuit is referred to as the “Two-wire method”. A maintained contact type of pilot
device like presence sensor, thermostat, or float switch is used in the two-wire
method of wiring the control circuit.
Method 2: Unlike the two-wire method, the “Three-wire method” of wiring the
control circuit uses a holding circuit contact and the momentary contact pilot
devices.
Industrial Control
Basics:
Part 1, Contactors
Industrial Control
Basics: Part 2,
Overload Relays
Industrial Control
Basics: Part 3,
Starters
The Benefits of Type E/F
Motor Protection
Circuit Breakers
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
Application
NEMA vs IEC Motor
Controls
Understanding
IP Ratings
32
