§ 869. — Underground low and mediumvoltage alternating current circuits.
[Laws in effect as of January 24, 2002]
[Document not affected by Public Laws enacted between
January 24, 2002 and December 19, 2002]
[CITE: 30USC869]
TITLE 30--MINERAL LANDS AND MINING
CHAPTER 22--MINE SAFETY AND HEALTH
SUBCHAPTER III--INTERIM MANDATORY SAFETY STANDARDS FOR UNDERGROUND COAL
MINES
Sec. 869. Underground low- and medium-voltage alternating
current circuits
(a) Circuits providing power for three-phase equipment; circuit breakers
Low- and medium-voltage power circuits serving three-phase
alternating current equipment shall be protected by suitable circuit
breakers of adequate interrupting capacity which are properly tested and
maintained as prescribed by the Secretary. Such breakers shall be
equipped with devices to provide protection against under-voltage,
grounded phase, short circuit, and over-current.
(b) Circuits used underground; direct neutral grounds; ground conductors
for frames; exceptions; grounding resistors
Low- and medium-voltage three-phase alternating-current circuits
used underground shall contain either a direct or derived neutral which
shall be grounded through a suitable resistor at the power center, and a
grounding circuit, originating at the grounded side of the grounding
resistor, shall extend along with the power conductors and serve as a
grounding conductor for the frames of all the electrical equipment
supplied power from that circuit, except that the Secretary or his
authorized representative may permit ungrounded low- and medium-voltage
circuits to be used underground to feed such stationary electrical
equipment if such circuits are either steel armored or installed in
grounded rigid steel conduit throughout their entire length. The
grounding resistor, where required, shall be of the proper ohmic value
to limit the ground fault current to 25 amperes. The grounding resistor
shall be rated for maximum fault current continuously and insulated from
ground for a voltage equal to the phase-to-phase voltage of the system.
(c) Inclusion of fail safe ground check circuits in resistance ground
systems; operative functions; time extension; couplers for power
circuits; guidelines for construction
Six months after the operative date of this subchapter, low- and
medium-voltage resistance grounded systems shall include a fail safe
ground check circuit to monitor continuously the grounding circuit to
assure continuity which ground check circuit shall cause the circuit
breaker to open when either the ground or pilot check wire is broken, or
other no less effective device approved by the Secretary or his
authorized representative to assure such continuity, except that an
extension of time, not in excess of twelve months, may be permitted by
the Secretary on a mine-by-mine basis if he determines that such
equipment is not available. Cable couplers shall be constructed so that
the ground check continuity conductor shall be broken first and the
ground conductors shall be broken last when the coupler is being
uncoupled.
(d) Disconnecting devices installed in conjunction with circuit
breakers; purpose; trailing cables for mobile equipment;
guidelines for construction; time extension; splices
Disconnecting devices shall be installed in conjunction with the
circuit breaker to provide visual evidence that the power is
disconnected. Trailing cables for mobile equipment shall contain one or
more ground conductors having a cross sectional area of not less than
one-half the power conductor, and, six months after the operative date
of this subchapter, an insulated conductor for the ground continuity
check circuit or other no less effective device approved by the
Secretary or his authorized representative to assure such continuity,
except that an extension of time, not in excess of twelve months may be
permitted by the Secretary on a mine-by-mine basis if he determines that
such equipment is not available. Splices made in the cables shall
provide continuity of all components.
(e) Connections of single phase loads
Single phase loads shall be connected phase to phase.
(f) Circuit breakers; markings
Circuit breakers shall be marked for identification.
(g) Trailing cables for medium voltage circuits; guidelines for
construction
Trailing cables for medium voltage circuits shall include grounding
conductors, a ground check conductor, and ground metallic shields around
each power conductor or a grounded metallic shield over the assembly,
except that on equipment employing cable reels, cables without shields
may be used if the insulation is rated 2,000 volts or more.
(Pub. L. 91-173, title III, Sec. 309, Dec. 30, 1969, 83 Stat. 782.)
References in Text
For the operative date of this subchapter, referred to in subsecs.
(c) and (d), see section 509 of Pub. L. 91-173, set out as an Effective
Date note under section 801 of this title.
Section Referred to in Other Sections
This section is referred to in section 861 of this title.
