Brochure
Table Of Contents
- Introduction
- Motor Failure and Protection
- Trip Class Designation
- Withstand Ratings
- Thermal Overload Relay
- Melting Alloy
- Non-Compensated Bimetallic
- Automatic Reset
- Ambient Temperature Compensated Bimetallic
- Thermal Overload Relay Trip Characteristics
- Solid State Overload Relay
- Additional Standard Features
- Optional Features
- Additional Standard Features
- Optional Features
- General
- Nameplate Versus NEC Full-load Current
- Service Factor
- Motor Branch Circuit Design
- Overload Relays
- Hand Reset Melting Alloy
- Accessories
- Isolated Auxiliary Contacts for Motor Logic Overload Relays
- DIN Adapter
- Lug-Lug/Lug-Extender Kits
- Remote Reset Module
- 4 – 20 ma DC Communication Module
- Contact Units for Melting Alloy Type Overload Relays
- Melting Alloy Overload Relay Jumper Strap Kits
- Bimetallic Overload Relays
- Motor Logic™ – Solid State Overload Relay
© 1998 Square D All Rights Reserved
20
5/98
Thermal Unit Selection
Quick Trip Thermal Unit Selection
To select Type FB quick blow trip thermal units, the
selection table for a standard Type B thermal unit
may be used with the following modifications: for
continuous rated motors having service factors of
1.15 to 1.25, select thermal units from the
standard Type B table using 93% (102% for Class
8198) of the full load current shown on the motor
nameplate and then substitute a FB for the B in
the thermal unit type number.
Example: A motor with a full load current of 14
amps controlled by an 8536 SCG3 would require
B22 thermal units for a standard trip application
and FB19.5 thermal units for quick trip
applications. The FB is selected by multiplying 14
amps times 93% for 13.02 amps and using this
value to select B19.5. Then add the F prefix to
arrive at FB19.5.
For continuous rated motors having a service
factor of 1.0, select thermal units in the same
manner using 84% (93% for Class 8198) of full
load current shown on the motor nameplate.