30 CFR § 7.407 Test for flame resistance of electric cables and cable splices.
(a)Test procedure. (1) For electric cables, prepare 3 specimens of
cable, each 3 feet in length, by removing 5 inches of jacket material and
2 inches of conductor insulation from both ends of each test specimen.
For splices, prepare a splice specimen in each of 3 sections of
MSHA-approved flame-resistant cable. The cable shall be of the type that the
splice kit is designed to repair. The finished splice shall not exceed 18
inches or be less than 6 inches in length for test purposes. The spliced
cables shall be 3 feet in length with the midpoint of the splice located 14
inches from one end. Both ends of each of the spliced cables shall be
prepared by removing 5 inches of jacket material and 2 inches of conductor
insulation. The type, amperage, voltage rating, and construction of the
cable shall be compatible with the splice kit design. Each splice shall be
made in accordance with the instructions provided with the splice kit.
(2) Prior to testing, condition each test specimen for a
minimum of 24 hours at a temperature of 70 ±10°F (21.1 ±5.5°C) and a relative
humidity of 55 ±10 percent. These environmental conditions shall be maintained
during testing.
(3) For electric cables, locate the sensing element of the
temperature measuring device 26 inches from one end of each test specimen.
For splices, locate the sensing element 12 inches from the midpoint of the
splice and 10 inches from the end of the cable. The sensing element must be
secured so that it remains in direct contact with the metallic portion of the
power conductor for the duration of the flame-resistant test. If a
thermocouple-type temperature measuring instrument is used, connect the
sensing element through the cable jacket and power conductor insulation.
Other means for monitoring conductor temperature may be used, provided the
temperature measurement is made at the same location. If the jacket and
conductor insulation must be disturbed to insert the temperature measuring
device, each must be restored as closely as possible to its original
location and maintained there for the duration of the testing.
(4) Center the test specimen horizontally in the test
chamber on the three rods. The three rods shall be positioned perpendicular
to the longitudinal axis of the test specimen and at the same height, which
permits the tip of the inner cone from the flame of the gas burner, when
adjusted in accordance with the test procedure, to touch the jacket of the
test specimen. The specimen shall be maintained at this level for the
duration of the flame test. The two outermost rods shall be placed so that 1
inch of cable jacket extends beyond each rod. For electric cables, the third
rod shall be placed 14 inches from the end of the test specimen nearer the
temperature monitoring location on the specimen. For splices, the third rod
shall be placed between the splice and the temperature monitoring location at
a distance 8 inches from the midpoint of the splice. The specimen shall be
free from external air currents during testing.
(5) Adjust the gas burner to give an overall blue flame 5
inches high with a 3-inch inner cone. There shall be no persistence of yellow
coloration.
(6) Connect all power conductors of the test specimen to
the current source. The connections shall be secure and compatible with the
size of the cable's power conductors in order to reduce contact
resistance.
(7) Energize all power conductors of the test specimen
with an effective heating current value of 5 times the power conductor
ampacity rating (to the nearest whole ampere) at an ambient temperature of
104 °F (40 °C).
(8) Monitor the electric current through the power
conductors of the test specimen with the current measuring device. Adjust the
amount of heating current, as required, to maintain the proper effective
heating current value within ±5 percent until the power conductors reach a
temperature of 400 °F (204.4 °C).
(9) For electric cables, apply the tip of the inner cone
from the flame of the gas burner directly beneath the test specimen for 60
seconds at a location 14 inches from one end of the cable and between the
supports separated by a 16 inch distance. For splices, apply the tip of the
inner cone from the flame of a gas burner for 60 seconds beneath the
midpoint of the splice jacket.
(10) After subjecting the test specimen to external flame
for the specified time, fully remove the flame of the gas from beneath the
specimen without disturbing air currents within the test chamber.
Simultaneously turn off the heating current.
(11) Record the amount of time the test specimen continues
to burn after the flame from the gas burner has been removed. The duration of
burning includes the burn time of any material that falls from the test
specimen after the flame from the gas has been removed.
(12) Record the length of burned (charred) area of each
test specimen measured longitudinally along the cable axis.
(13) Repeat the procedure for the remaining two
specimens.
(b)Acceptable performance. Each of the three test specimens shall
meet the following criteria:
(1) The duration of burning shall not exceed 240
seconds.
(2) The length of the burned (charred) area shall not
exceed 6 inches.
