Program Policy Manual - VOLUME V - Mine Safety and Health ...

MSHA PROGRAM POLICY MANUAL VOLUME V
2. all overhead high-voltage disconnect switches which
are operated from the ground by means of mechanical
linkage. (See Section 77.704-9 for requirements for
high-voltage switches.)
Enclosed power control switches such as portable circuit
breakers of switch houses that are supplied power from a
resistance-grounded system, as required by Section 77.802 or
77.901, are not considered to pose a shock hazard.
Grounded metal mats or plates may not be used instead of
insulating mats in front of live front switchboards.
Insulating mats or platforms installed at high-voltage
installations shall be rated for not less than the phase-tophase
voltage of the circuit. Insulating mats can provide
such additional safety if placed at low-voltage linestarters,
fuse boxes, and other low-voltage switchgear containing
renewable parts.
77.516 Electric Wiring and Equipment; Installation and
Maintenance
Section 77.516 requires, in addition to compliance with
Sections 77.503 and 77.506, that electric equipment installed
after June 30, 1971, meet the requirements of the NEC. The
NEC has been incorporated into MSHA standards to address
wiring and wiring methods for surface facilities and
structures not specifically covered in Part 77. The NEC will
continue to be applied to surface facilities and structures
other than the specified excavation equipment. The NEC
contains safety guidelines which are not specifically
tailored to surface mine excavation equipment and conductors,
but which cover a much broader scope. While Section 77.516
addresses wiring and electric equipment installed after June
30, 1971, on surface mining machines, many provisions of the
NEC are not applicable to the wiring methods, types of
equipment, and conditions on these machines. For example,
certain excavation equipment designed and installed since
June 30, 1971, is not compatible with the requirements of the
1968 NEC. Therefore, strict application of and compliance
with the NEC for the wiring methods used on surface mine
excavation equipment is not practicable.
Wiring and electric equipment installed after June 30, 1971,
on-board electric or diesel-powered surface excavation
equipment are not required to comply with the NEC under
Section 77.516, although mine operators are free to rely on
it as a guideline. This policy applies to equipment such as
draglines, shovels, dozers, bucket wheel excavators, mobile
February 2003 (Release V-33) 180