BS 764-1990 pdf free.Specification for Automatic change-overcontactors for emergency lightingsystems.
BS 764 This British Standard specifies d.c. and single-phase a.c.automatic double-pole change-overcontactors for low voltages up to 250 V employed inconjunction with storage batteries or other alternative source of supply, to provide a means ofautomatically changing the current supplied tosafety lights from the normal source to the alternative source when the normal source fails, andof 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 1Appendix B lists information to be supplied to themanufacturer with the enquiry and/or order.
NOTE 2The titles of the publications referred to in thisstandard are listed on the inside back cover.
For the purposes of this British Standard, thefollowing definitions apply.
automatic change-over contactor a complete apparatus for effecting automaticchange-over of the safety lights from the normalsupply to the alternative supply when the normalsupply fails, and for returning the safety lights tothe normal supply when this supply is restored. Thereturn operation may be effected through the agency of a relay which, if employed, is an integralpart of the contactor.safety lights lights which are normally connected to normalsupply and are changed over to the alternativesupply when the normal supply fails, e.g.the safetylights specified under the Cinematograph Regulations.
main contactor apparatus constructed in accordance with thisspecification, excepting the relay if employed.Where the complete automatic change-over contactor is intended, this is made clear in relevantclauses.a voltage dependent relay, the function of which is tocause the main contactor to change from the emergency to the normal position when the mainsupply voltage has recovered to a particular value.contactor coil the shunt connected coil energized from the normalsupply, which causes the main contactor either tochange to, or to remain in, the normal position2.6.
relay coil the shunt connected coil, energized from the normalsupply, which causes the relay contacts to move toone of their two positions.BS 764 pdf download.