Electric Motor Control Basics - Book - Page 41
Industrial Control Basics: Part 3, Starters
3. Overload Protection: When a motor draws more current than it is designed to, an
overload condition is caused. The main objective of an overload relay is to detect the
excess currents. When an overload is detected, the auxiliary contact of the overload
relay opens the circuit and prevents the motor from burning out or overheating.
Electronic or electromechanical overload relays are used in combination with a
contactor to provide the required overload protection.
4. Disconnecting and Breaking: In order to prevent an unintended restart, it is
required to disconnect the motor from the main power circuit. In order to safely
perform maintenance on a motor or starter, a motor must be able to switch off and be
isolated from the power. The disconnect switch of the circuit provides this function.
Disconnecting and breaking is provided by a disconnect switch or circuit breaker in a
Combination Motor Controller (or can be installed remotely from the starter).
Part 1, Contactors
Basics: Part 2,
Basics: Part 3,
The Benefits of Type E/F
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
NEMA vs IEC Motor