ensured by use of one of the following:
(1) Mechanically sequenced regulator bypass switch(es)
(2) Mechanical interlocks
(3) Switching procedure prominently displayed at the switching location
490.24 Minimum Space Separation. In field-fabricated installations, the minimum air separation between bare live
conductors and between such conductors and adjacent grounded surfaces shall not be less than the values given in
Table 490.24. These values shall not apply to interior portions or exterior terminals of equipment designed, manufactured, and tested in accordance with accepted national standards.
III. Equipment — Metal-Enclosed Power Switchgear and
Industrial Control Assemblies
490.30 General. This part covers assemblies of metal- enclosed power switchgear and industrial control, including but not limited to switches, interrupting devices and their control, metering, protection and regulating equipment, where an integral part of the assembly, with associated interconnections and supporting structures. This part also in cludes metal-enclosed power switchgear assemblies that form a part of unit substations, power centers, or similar equipment.
490.31 Arrangement of Devices in Assemblies. Arrange- ment of devices in assemblies shall be such that individual components can safely perform their intended function without adversely affecting the safe operation of other components in the assembly.
490.32 Guarding of High-Voltage Energized Parts Within a Compartment. Where access for other than vi- sual inspection is required to a compartment that contains energized high-voltage parts, barriers shall be provided to prevent accidental contact by persons, tools, or other equipment with energized parts. Exposed live parts shall only be permitted in compartments accessible to qualified persons. Fuses and fuseholders designed to enable future replacement without de-energizing the fuseholder shall only be permitted for use by qualified persons.
490.33 Guarding of Low-Voltage Energized Parts Within a Compartment. Energized bare parts mounted on doors shall be guarded where the door must be opened for maintenance of equipment or removal of draw-out equipment.
490.34 Clearance for Cable Conductors Entering En- closure. The unobstructed space opposite terminals or opposite raceways or cables entering a switchgear or control assembly shall be adequate for the type of conductor and method of termination.
490.35 Accessibility of Energized Parts.
(A) High-Voltage Equipment. Doors that would provide unqualified persons access to high-voltage energized parts shall be locked.
(B) Low-Voltage Control Equipment. Low-voltage control equipment, relays, motors, and the like shall not be installed in compartments with exposed high- voltage energized parts or high-voltage wiring unless either of the following conditions is met:
(1) The access means is interlocked with the high- voltage switch or disconnecting means to prevent the access means from being opened or removed.
(2) The high-voltage switch or disconnecting means is in the isolating position.
(C) High-Voltage Instruments or Control
Transformers
and Space Heaters. High-voltage instrument or
control
transformers and space heaters shall be permitted to
be installed in the high-voltage compartment without
access restrictions beyond those that apply to the
high-voltage compartment generally.