BS 4999-111:1987

Foreword
Committees responsible
Introduction
Specification
1 General
1.1 Scope
1.2 Definitions
2 Requirements for devices fitted into motor windings
2.1 General
2.2 Classification
2.3 Motors fitted with thermistors
2.4 Motors fitted with thermostats
3 Temperature sensitive resistors (thermistors)
3.1 General
3.2 Characteristics
3.3 Ability to withstand motor manufacturing processes
3.4 Dimensions
3.5 Leads
3.6 Marking
3.7 Type tests
3.8 Routine tests
4 Thermistor control unit
4.1 Terminals
4.2 Standard operating conditions
4.3 Drop-off (trip) and pick-up (re-set) resistance
4.4 Thermistor applied voltage
4.5 Abnormal conditions
4.6 Minimum voltage hold-in
4.7 Switching rating
4.8 Type tests
4.9 Routine tests
5 Thermostats
5.1 General
5.2 Characteristics
5.3 Ability to withstand motor manufacturing processes
5.4 Leads
5.5 Marking
5.6 Switching rating
5.7 Overload switching performance
5.8 Type tests on thermostats
Appendix
A Typical characteristic of PTC type thermistor
Tables
1 Winding temperature
2 Recommended reference temperatures for thermistors

Classifies types of protection, specifies winding temperatures for steady overload and stalled conditions. Recommends thermistor reference temperatures. Characteristics for thermostats, thermistors and thermistor control units with appropriate tests. Thermistors are of positive temperature coefficient. An appendix gives typical characteristic curve.