Selecting Slow Trip Thermal Units

To select Type SB slow 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.
Substitute an SB for the B in the thermal unit type number.

Example:

A motor with a full-load current of 12 A controlled by an 8536SCG3 would require B22 thermal units for standard trip applications and SB19.5 thermal units for slow trip applications. The SB is selected by multiplying 12 A times 93% for 11.16 A and using this value to select B19.5. Then, add the S prefix to arrive at SB19.5.

For continuous rated motors having a service factor of 1.0, select thermal units from the standard Type B table using 84% (93% for Class 8198) of full-load current shown on the motor nameplate.

NOTE: SB thermal units are used on Size 0, 1, 2, and only some Size 3 applications. Check thermal unit tables for current ranges.

Thermal Unit Trip Types

Melting Alloy
Type of Trip	Thermal Unit Type
Standard	A
	B
	C
	CC
	DD
Quick	FB
Slow	SB

Selection of Thermal Units for Special Applications

Class of Controller	Continuous Duty Motor Service Factor	Melting Alloy
		Ambient Temperature of Motor
		Same as Controller Ambient	Constant 10 °C (18 °F) Higher Than Controller Ambient	Constant 10 °C (18 °F) Lower Than Controller Ambient
		Full Load Current Multiplier
All Classes, Except 8198	1.15 to 1.25	1.0	0.9	1.05
All Classes, Except 8198	1.0	0.9	0.8	0.95
Class 8198	1.15 to 1.25	1.1	1.0	1.15
Class 8198	1.0	1.0	0.9	1.05