Brochure

© 1998 Square D All Rights Reserved
12
5/98
Thermal Overload Relays – NEMA Rated
Application Data
Once tripped, the thermal overload relay will not
reset until it has cooled, automatically allowing the
motor to cool before it can be re-started.
Square D manufactures two basic types of
thermal overload relays, the melting alloy and the
bimetallic. In some types, the bimetallic is
available in both non-compensated and ambient
temperature-compensated versions. In both
melting alloy and bimetallic, single element and
three element overloads are available.
Motor Logic Solid State overload relays use an
electronic method of detection, which responds
directly to the motor current. When tripped the
overload relay may be reset either manually or
remotely using the Remote Reset Module. The
Solid State overload relay provides overload
protection only for three phase motors rated up to
600 volts AC.
The Solid State overload relay provides protection
for phase loss and phase unbalance. In addition,
this overload relay is ambient insensitive. The
Solid State overload relay is available as a
separate trip Class 10 or 20 and as a selectable
trip Class 10/20 device.
The Motor Logic solid state overload relay must
be selected based on the FLA of the motor it is to
protect. Applications involving a motor with an
FLA less than 1.5 amps can be addressed by
passing multiple looped turns of the motor leads
through the current transformer windows.
Hand Reset Melting Alloy
Application
Hand reset melting alloy overload relays use a
eutectic alloy solder which responds to the heat
produced in a heater element by the motor
current. When tripped, the overload relay may be
reset manually after allowing a few minutes for the
motor and relay to cool and the solder to solidify.
Square D’s one-piece thermal unit construction
will provide overload protection for the majority of
motors. Repeated tripping does not affect the
original calibration. Melting alloy thermal units are
available in three designs: standard trip, slow trip
and quick trip.
Standard Trip (Class 20)–All standard trip thermal
units provide trip characteristics for normal motor
acceleration up to approximately 7 seconds on a
full voltage start.
Slow Trip (Class 30) – Type SB thermal units
provide trip characteristics for motor acceleration
up to approximately 12 seconds on a full voltage
start. The motor should be suitable for extended
starting periods.
Quick Trip (Class 10) – Type FB thermal units are
used to protect hermetically sealed, submersible
pump and other motors which can endure locked
rotor current for a very short time, or motors which
have a low ratio of locked rotor to full load current.
Replaceable Contacts – The contact modules of
Type S, F and G overload relays are replaceable.
Refer to Page 13.
Alarm Contacts – Contact modules with one N.O.
and one N.C. contact are available for Type S, F,
an G overload relays. For Type S, specify Form
Y34-2; for Types F and G, specify Form Y34.
Y34-2 indicates a four terminal isolated contact
module and Y34 indicates a three terminal module
with a common terminal between the N.O. and
N.C. contacts. Refer to Page 13.
Contact Ratings – For the overload relay control
circuit contact ratings refer to Page 13.
Cutaway View of Standard
Trip Melting Alloy
Thermal Unit
Class 9065 Type SEO5
Three-Pole Construction
Class 9065 Type CO1
Single Pole Construction