What is the difference between B thermal melting alloy heaters and SB type Melting alloy heaters?
NEMA style Overload Relays
B heaters have a Class 10 (10 second) trip and Class 20 (20 second) trip. SB melting alloy heaters have a Class 30 (30 second) trip.
Slow Trip Thermal Unit Selection (SB thermal units are used on Size 0, 1, 2 and only some Size 3 applications. Check thermal unit tables for current ranges.
To select Type SB slow trip thermal units, use the selection table for a standard Type B thermal unit with the following modifications: For
continuous rated motors with 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 motor nameplate full load current; then substitute SB for the B in the thermal unit type number. 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