(a)
Ungrounded current-carrying parts of electrical utilization equipment, such as
bus bars, conductors, and terminals, operating at over 150 volts to ground and
not isolated by elevation at least 8 feet above floor line shall, if
practicable, be provided with suitable permanent enclosures or other guards
arranged so as to prevent persons or conducting objects from inadvertently
coming in, or being brought into, contact with the parts in question and at the
same time so as to permit ready access to authorized persons for making
adjustments or repairs, unless excepted under the provisions of subsection (b).
Enclosures may consist of suitable casings or suitable insulating coverings.
The continuous insulating covering of conductors should be depended upon only
when the circuit is grounded or entirely unexposed to leakage or induction from
higher voltage circuits, and when it is impracticable to install more suitable
guards. It should be depended upon then only when the covering is not exposed
to liability of mechanical injury, and is very substantial, thoroughly dry, and
contains no noninsulating flameproofing compound or oil-soaked rubber. It is
recommended that in addition to the protection afforded by such coverings the
insulating mats or platforms called for in subsection (b) be used. If it is
necessary that covers, casings, or barriers at any time be removed from the
otherwise exposed current-carrying parts which they guard, while these parts
are alive, the covers, casings or barriers should be of insulating material, or
so arranged that they are not readily brought in contact with the live parts.
Mats may be of wood, held together by wood pins, or of cork matting, linoleum
or rubber. The material and construction should be suitable for the voltage
concerned and for the prevailing conditions. If subject to moisture or to
accumulations of conducting dust, flyings, or chips, mats should present
surfaces minimizing the hazards from these sources. Reference should be made to
§
39.214 (relating to guarding
conductors).
(b) If
current-carrying parts at over 150 volts to ground are necessarily exposed,
ungrounded, and within 8 feet from the floor line, surrounding conducting
floors and other noncurrent-carrying surfaces within reach shall be covered
with suitable insulating platforms, mats or other insulating devices. Reference
should also be made to §
39.198 (relating to working space
about electrical equipment). The guarding of current-carrying parts obviates
the necessity for such insulating devices, and when the use of the latter is
impracticable, from the nature of the location or processes carried on, guards
should always be used.
(c) Except
on fenced rights of way or other locations to which only qualified persons are
admitted, trolley or crane collector wires and third rails, whether indoors or
out, shall be so isolated by elevation, or be provided with suitable guards so
arranged that persons do not inadvertently touch the current-carrying parts
while in contact with the ground, or with conducting material connected to the
ground, and shall be provided with warning signs effective whenever the
conductors are alive. Damp wood, concrete floors, and metal parts of crane cabs
are considered as grounded. Trolley-contact conductors indoors shall be so
supported that in case of a single break, contact with the floor is not made.
Reference should be made to §
39.106 (relating to isolating live
parts by elevation).
(d) Bare parts
at different potentials shall be effectively separated. Such parts in circuits
of large capacity or operating at over 300 volts shall, if practicable, unless
provided with the enclosure or other guard specified in subsection (a), be
provided with suitable barriers, if otherwise they would be liable to be short
circuited by tools or other conducting objects.
