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(B) Support Methods. One of the following methods of
support shall be used.
(1) By clamping devices constructed of or employing
insulating wedges inserted in the ends of the
raceways. Where clamping of insulation does not
adequately support the cable, the conductor also
shall be clamped.
(2) By inserting boxes at the required intervals in which
insulating supports are installed and secured in a
satisfactory manner to withstand the weight of the
conductors attached thereto, the boxes being
provided with covers.
(3) In junction boxes, by deflecting the cables not less
than 90 degrees and carrying them horizontally to a
distance not less than twice the diameter of the cable,
the cables being carried on two or more insulating
supports and additionally secured thereto by tie
wires if desired. Where this method is used, cables
shall be supported at intervals not greater than
20 percent of those mentioned in the preceding
tabulation.
(4) By a method of equal effectiveness.
300.21 Spread of fire or Products of Combustion
Electrical installations in hollow spaces, vertical shafts, and
ventilation or air-handling ducts shall be made so that the
possible spread of fire or products of combustion will not be
substantially increased. Openings around electrical
penetrations through fire-resistance rated walls, partitions,
floors, or ceilings shall be fire-stopped using approved
methods to maintain the fire-resistance rating.
FPN: Directories of electrical construction materials published
by qualified testing laboratories contain many listing installa-
tion restrictions necessary to maintain the fire-resistive rating
of assemblies where penetrations or openings are made.
Building codes also contain restrictions on membrane
penetrations on opposite sides of a fire-resistance-rated
wall assembly. An example is the 600 mm (24 in.) minimum
horizontal separation that usually applies between boxes
installed on opposite sides of the wall. Assistance in
complying with 300.21 can be found in building codes,
fire resistance directories, and product listings.
300.22 Wiring in Ducts, Plenums, and Other
Air-Handling Spaces