Electric Motor Control Basics - Book - Page 25
Industrial Control Basics: Part 2, Overload Relays
2. Eutectic Overload Relay
This type of overload relay is comprised of a heater winding, a mechanical mechanism
for activation of a tripping mechanism, and a eutectic alloy. A eutectic alloy is a
combination of two or more materials, which solidifies or melts at a specific known
temperature.
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
In the the overload relay, the eutectic alloy is contained in a tube, which is often used
along with a spring loaded ratchet wheel to activate the tripping mechanism during
the overload operations. The motor current passes through the small heater winding.
During the overload, the eutectic alloy tube is heated by the heater winding. The alloy
melts due to the heat, thereby releasing the ratchet wheel, and allowing it to turn.
This action initiates the opening of the closed auxiliary contacts in the overload relay.
NEMA vs IEC Motor
Controls
Understanding
IP Ratings
25
