UL Standard for Safety Enclosed and Dead-Front Switches
|Publication Date:||25 February 2004|
These requirements cover individually enclosed air switches, rated 4000 A or less at 600 V or less, having all current-carrying parts enclosed, manually operable by means of external handles, and intended to be employed in accordance with the national installation codes listed in Appendix A, Ref. No.1.
As used in this Standard, the term switch is intended to mean an enclosed switch or deadfront switch unless specifically stated otherwise.
These requirements also cover deadfront switches that have all current-carrying parts enclosed when mounted in an enclosed panelboard, deadfront switchboard, or the like. These switches are manually operable by means of external handles and are intended to be employed in accordance with the national installation codes listed in Appendix A, Ref. No.1.
These requirements cover enclosed switches with or without provision for fuses suitable for use as branch circuit, feeder, and service overcurrent protection.
The following fuses are deemed suitable for use as branch circuit, feeder, and service overcurrent protection:
a) Cartridge Fuses (Ref. Appendix B, Low-Voltage Fuses - Parts 1-10, 12 and 15);
b) Plug Fuses (Ref. Appendix B, Low-Voltage Fuses - Parts 1 and 11); and
c) Special Purposes Fuses marked as meeting the performance specifications of a specific Class Fuse.
These requirements cover enclosed switches intended for general use and having ampere ratings, with or without horsepower or kilowatt ratings, and enclosed switches intended for motor-circuit use only and having horsepower or kilowatt ratings but no general-use ampere ratings.
These requirements cover double-throw switches intended for use in optional standby systems (see Appendix A, Ref. No. 1).
These requirements cover fused electrically tripped switches rated over 600 A and rated 600 A or less employing Class J, R or T fuses.
These requirements also cover electrically tripped switches that have been investigated to determine their acceptability for ground-fault protection when combined with ground-fault sensing and relaying equipment as follows:
a) Switches for use with Class I ground-fault sensing and relaying equipment include those that are capable of interrupting 12 times their rated current or that have integral means to prevent disconnecting as levels of fault current exceeding the contact interrupting capability of the switch.
b) Switches for use with Class II ground-fault sensing and relaying equipment are capable of interrupting 10 times their rated current and are for use in ground-fault protection systems in which means to prevent disconnecting at levels of fault current exceeding the contact interrupting capability of the switch are incorporated within the ground-fault sensing and relaying equipment when combined with Class I and II ground-fault sensing and relaying equipment.
These requirements do not cover:
a) Common forms of snap switches,
b) Switches having features intended primarily for the starting and protection of motors, including the switches arranged to shunt out fuses during the starting of motors,
c) Switches provided with automatic trips for opening them and constructed to afford overload protection without other circuit breakers or fuses,
d) Devices in which the pulling of fuses or the removal of a detachable pullout member is designed to accomplish a switching operation, or
e) Circuit breakers, molded-case switches, magnetic-only circuit interrupters, instantaneous-only circuit breakers, and supplementary protectors.