Electric Motor Control Basics - Book - Page 26
Industrial Control Basics: Part 2, Overload Relays
Eutectic overload relays can only be manually reset after tripping. This reset is usually
done through a reset button, which is positioned on the cover of the relay. The heater
unit installed on the relay is chosen on the basis of the full load current of the motor.
3. Solid State Overload Relay
These relays are commonly referred to as electronic overload relays. Unlike the
bimetallic and eutectic overload relays, these electronic overload relays measure
current electronically. Although available in various designs, they share common
features and benefits. The heaterless design is one of the main advantages of these
relays. This design helps reduce the costs and efforts of installation. In addition, the
heaterless design is insensitive to the change in ambient temperatures, which helps
minimize nuisance tripping. These relays also provide protection from phase loss –
more effectively than bimetallic or eutectic alloy overload relays. These relays can
easily detect a loss of phase, and operate an auxiliary contact to open the motor
control circuit. Solid state overload relays enable easy adjustment of trip times and
set points.
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
26
