BS 764:1990

Foreword
Committees responsible
Specification
1 Scope
2 Definitions
3 Characteristics
4 Design, construction and marking
5 Tests
Appendices
A Methods for measurement of temperature
B Information to be supplied to the manufacturer with
   enquiry and/or order
Tables
1 Minimum contact force
2 Limits of temperature rise for contacts and
   conductors
3 Limits of temperature rise for coils
Figure
1 Diagram of typical circuit for test for making and
   breaking capacity

Design and performance requirements for d.c. and single-phase a.c. double-pole change-over contactors for low-voltages up to 250 volts and a range of standard current ratings, which are used to provide the automatic transfer of current supplied to safety lights from the normal source to an alternative source when the normal source fails; reconnection is automatic when the normal supply conditions are restored.

This British Standard specifies d.c. and single-phase a.c. automatic double-pole change-over contactors for low voltages up to 250 V employed in conjunction with storage batteries or other alternative source of supply, to provide a means of automatically changing the current supplied to safety lights from the normal source to the alternative source when the normal source fails, and of reconnecting the safety lights to the normal source when this source is restored.

This standard does not apply to three-phase a.c. automatic change-over contactors.

NOTE 1 Appendix B lists information to be supplied to the manufacturer with the enquiry and/or order.

NOTE 2 The titles of the publications referred to in this standard are listed on the inside back cover.