110.27 Guarding of Live Parts.
(A) Live Parts Guarded Against Accidental Contact.
Except as elsewhere required or permitted by this Code,
live parts of electrical equipment operating at 50 volts or
more shall be guarded against accidental contact by approved
enclosures or by any of the following means:
(1) By location in a room, vault, or similar enclosure that is
accessible only to qualified persons.
(2) By suitable permanent, substantial partitions or screens
arranged so that only qualified persons have access to
the space within reach of the live parts. Any openings
in such partitions or screens shall be sized and located
so that persons are not likely to come into accidental
contact with the live parts or to bring conducting objects
into contact with them.