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.
