(a) A tool or switch held in the operator's hand or supported against
his body will not be approved with a nameplate rating exceeding 300 volts
direct current or alternating current.
(b) A battery-powered machine shall not have a nameplate rating
exceeding 240 volts, nominal (120 lead-acid cells or equivalent).
(c) Other direct-current machines shall not have a nameplate rating
exceeding 550 volts.
(d) An alternating-current machine shall not have a nameplate rating
exceeding 660 volts, except that a machine may have a nameplate rating
greater than 660 volts but not exceeding 4,160 volts when the following
conditions are complied with:
(1) Adequate clearances and insulation for the particular
voltage(s) are provided in the design and construction of the equipment, its
wiring, and accessories.
(2) A continuously monitored, failsafe grounding system is
provided that will maintain the frame of the equipment and the frames of all
accessory equipment at ground potential. Also, the equipment, including its
controls and portable (trailing) cable, will be deenergized automatically
upon the occurrence of an incipient ground fault. The ground-fault-tripping
current shall be limited by grounding resistor(s) to that necessary for
dependable relaying. The maximum ground-fault-tripping current shall not
exceed 25 amperes.
(3) All high voltage switch gear and control for equipment
having a nameplate rating exceeding 1,000 volts are located remotely and
operated by remote control at the main equipment. Potential for remote
control shall not exceed 120 volts.
(4) Portable (trailing) cable for equipment with nameplate
ratings from 661 volts through 1,000 volts shall include grounding
conductors, a ground check conductor, and grounded metallic shields around
each power conductor or a grounded metallic shield over the assembly; except
that on machines employing cable reels, cables without shields may be used if
the insulation is rated 2,000 volts or more.
(5) Portable (trailing) cable for equipment with nameplate
ratings from 1,001 volts through 4,160 volts shall include grounding
conductors, a ground check conductor, and grounded metallic shields around
each power conductor.
(6) MSHA reserves the right to require additional
safeguards for high-voltage equipment, or modify the requirements to
recognize improved technology.
