Electric Motor Control Basics - Book - Page 60
Applying Motor Control in a Wastewater Application
2. Overload Relay:
When a motor draws excess current, it is referred to as an overload. This may cause
overheating of the motor and damage the windings of the motor. Because of this,
it is important to protect the motor, motor branch circuit, and motor branch circuit
components from overload conditions. Overload or overheating is one of the major
reasons for pump failure. Overload Relays protect the pump’s motor from these
conditions.
Designed as electromechanical devices, overload relays are distinguished as
bimetallic, melting alloy, or solid-state electronic relays on the basis of their
construction.
Bimetallic overload relays are one of the most common types of overload protection
devices, and they feature adjustable trip points. Bimetallic overloads are engineered
for automatic reclosing and compensate to prevent ambient temperature changes.
In addition, these overload relays protect motors in extreme temperature
environments.
Advanced bimetallic overload relays feature manual or automatic reset and test
modes and a stop button that enables better device management. Many of these
relays possess single phase sensitivity, which helps protect motors against phase loss
conditions. These relays are provided in three trip class ratings:
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
60
