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    Single Circuit Breaker Switchhouses (Vacuum, Oil, and Air Types)

    1. If couplers are used, they shall be approved as meeting the requirements of Section 331(c) of the Act. The input gear-mounted coupler shall have male contacts. The output and feed-through gear-mount couplers shall have female contacts.
    2. There shall be a high-voltage visible disconnect switch that opens and grounds the disconnected phase leads. An unobstructed view of the position of all three blades shall be provided. The switch may be on the line or load side of the circuit breaker. Provisions shall be made to disconnect the outgoing pilot circuit. Each disconnecting switch shall have a function identifying tag. The high-voltage visible disconnect shall be interlocked to prevent operation under load. There shall be a means of mechanical lockout.
    3. The switchhouse frame shall be bonded (as defined by the current National Electric Code) to the system grounding medium.
    4. The outside surfaces shall be essentially of fireproof construction. Viewing windows shall be made of wire reinforced safety glass or an identifiable flame-retardant polycarbonate. Acrylics, such as Plexiglas, are prohibited.
    5. A push-to-activate, maintained contact, manual reset, emergency stop switch to trip the incoming power shall be provided.
    6. Barriers and interlock switches shall be used and so arranged to prevent inadvertent contact with energized components of a voltage of greater than 1,000 volts nominal.
    7. Circuit breaker:
      1. The circuit breaker shall be equipped with instantaneous and inverse time-limit phase overcurrent relays (on a minimum of two phases) and undervoltage, ground-fault current, and ground continuity check relays that provide for automatic tripping of the circuit breaker.
      2. Undervoltage: The undervoltage protection shall cause the undervoltage tripping solenoid to directly activate the circuit breaker tripping mechanism when the power circuit voltage is no less than 40% of nominal. Either of the following methods may be used to comply with this requirement:
        1. An undervoltage protective relay shall cause the undervoltage solenoid to directly activate the circuit breaker tripping mechanism when the power circuit voltage is no less than 40% of nominal. The undervoltage protective relay must be identified on the schematic and wiring diagrams. The identified relay may also serve another protective or control function.
        2. The solenoid may serve as both the undervoltage protective relay and the undervoltage tripping solenoid, if the solenoid directly causes the circuit breaker to trip when the power circuit voltage is no less than 40% of nominal.
      3. The opened or closed status of the circuit breaker shall be indicated.
    8. A separate ground-continuity check circuit originating at the branch circuit breaker shall be extended into the branch circuit.
    9. An ammeter capable of indicating current in each phase and a voltmeter capable of reading phase-to-phase voltage shall be provided at the circuit breaker.
    10. Ground-fault circuit-interrupters (GFCI) shall be used on all 110/220 VAC receptacles.
    11. Identifying tags for input, feed-through, and branch circuits shall be properly placed.
    12. The use of uninterruptible power supplies (UPS) and constant voltage transformers (CVT) in control circuits shall not compromise protection provided by undervoltage tripping solenoid.