Current through Register Vol. 54, No. 45, November 9, 2024
Section 39.105 - Guarding live parts(a) Protection shall be provided for persons near otherwise exposed ungrounded current-carrying parts of electrical supply equipment such as bus bars and other conductors on the terminals of generators and motors, operating at over 300 volts to ground and not effectively isolated by elevation unless these parts are away from passageways, and working spaces, used for frequent construction, inspection and repair.(b) If the working space about electrical equipment is less than that specified in § 39.104 (relating to working space about electrical equipment), suitable enclosures or barriers shall be provided to prevent inadventent contact with live parts. If such enclosures must be opened or barriers removed while the parts they guard are alive, surrounding floors shall be provided with suitable insulating platforms or mats, so placed that the operator may not readily touch the live parts without standing on the mat or platform.(1) Enclosures may consist of suitable casings or suitable insulating coverings. The insulating covering of conductors shall be depended upon only when it is impracticable to install more suitable guards and then only when very substantial, thoroughly dry, and containing no noninsulating flameproofing compound or oil-soaked rubber.(2) Barriers may consist of horizontal or vertical strips placed in front of current-carrying parts or of closely spaced partitions between such parts, extending beyond the exposed sides of the current-carrying parts.(3) If covers, casings or barriers are at any time removed while the parts which they guard are alive, they shall be of insulating material, or so arranged that they are not readily brought in contact with the live parts.(4) 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 provide surfaces minimizing the hazards from these sources.(c) If the specified working spaces are provided and the current-carrying parts are not guarded by enclosures or barriers, the insulating platforms or mats shall always be provided.(d) If the current-carrying parts operate at over 7500 volts the enclosing or barrier guards shall always be provided even if insulating mats are also provided. Enclosing or barrier guards not of grounded metal shall be of substantial material and spaced from the current-carrying parts not less than three times the needle-point sparking distance, at the voltage concerned, of the intervening air, oil, or other dielectric. This requirement shall not apply to direct-connected, motor-driven, high-tension, series generators, which for operating reasons have their frames insulated from ground.(e) Bare parts at different potentials shall be effectively separated. Such parts in circuits of large capacity or operating at above 7500 volts shall, unless provided with enclosures or other guards specified in subsection (b), be provided with suitable barriers, if practicable, so that they will not be short- circuited by tools or other conducting objects. This section cited in 34 Pa. Code § 39.160 (relating to guarding live parts of switches and automatic cut-outs not installed on switchboards); 34 Pa. Code § 39.144 (relating to guarding conductors); and 34 Pa. Code § 39.185 (relating to guarding live parts).