(a) Fire Resistivity of Electrical Vaults. The walls, roof, floors,
and doorways of vaults containing conductors and equipment over 600
volts, nominal, shall be constructed of materials that have adequate
structural strength for the conditions, with a minimum fire rating of 3
hours. The floors of vaults in contact with the earth shall be of
concrete that is not less than 100 mm thick, but where the vault is
constructed with a vacant space or other stories below it, the floor
shall have adequate structural strength for the load imposed on it and a
minimum fire resistance of 3 hours. For the purpose of this section,
studs and wallboards shall not be considered acceptable.
(b) Indoor Installations.
(1) In Places Accessible to Unqualified Persons. Indoor electrical
installations that are accessible to unqualified persons shall be made
with metal-enclosed equipment. Metal-enclosed switchgear, unit
substations, transformers, pull boxes, connection boxes, and other
similar associated equipment shall be marked with appropriate caution
signs. Openings in ventilated dry-type transformers or similar
openings in other equipment shall be designed so that foreign objects
inserted through these openings are deflected from energized parts.
(2) In Places Accessible to Licensed Electrical Practitioner or
Non-Licensed Electrical Practitioner Under the Supervision of a
Licensed Electrical Practitioner Only. Indoor electrical installations
considered accessible only to licensed electrical practitioner or non-licensed electrical practitioner under the supervision of a licensed
electrical practitioner in accordance with this section shall comply
with 1.10.3.5, 1.10.3.7, and 4.90.2.4.