66 Modern Commercial Wiring
Copyright Goodheart-Willcox Co., Inc.
Figure 5-14. FMC connectors are tightened around the conduit to maintain a solid fit. (RACO, Inc.)
Flexible Metal Conduit Fittings
90° Squeeze
Connector
Squeeze
Connector
Screw-In
Connector
Screw-In
Coupling
45° Squeeze
Connector
Rigid to Flexible
Threaded/Squeeze Coupling
EMT to Flexible
Compression/Squeeze Coupling
Figure 5-15. Support requirements for flexible metal conduit. No support is needed for lengths less than 3′. For longer lengths,
conduit is supported within 12″ of boxes, with a maximum space of 4′ – 6″ between supports.
3′ – 0″ max.
4′ – 6″ max. 12″ max.
10′ and within 3′ of outlets and fittings. The number of
conductors permitted in EMT is determined from the
tables in Chapter 9 of the Code. As with rigid metal
conduit and IMC, the total bends between raceway ends
must not exceed 360°.
Flexible metal conduit (FMC)
Flexible metal conduit is very similar in appearance to
armored cable. The primary differences are that FMC does
not come with conductors and the armor is more closely
interlocked.
This type of conduit may be installed in dry or wet
locations (providing the conductors are “W” rated and the
flex is liquidtight), hoistways, hazardous areas (Class I,
Division 2), and oil and gasoline areas if the conductor
insulation is suitable for the purpose.
FMC is manufactured in sizes 3/8″ to 4″ diameter, the
3/8″ size being permitted for use in connections not over
6′ in length for fixture whips, motor connections, under
plaster extensions, and manufactured wiring systems. In
such lengths or less, the FMC may serve as the equipment
grounding conductor. Flexible metal conduit fittings are
shown in Figure 5-14.
FMC must be supported at intervals less than 4′ - 6″
and within 12″ of each end. It should also be firmly
supported at every bend. Lengths of FMC less than 3′ do
not need to be supported, Figure 5-15. As with other
forms of conduit, the total bends between termination
points must not exceed 360°.
The maximum number of conductors permitted in
1/2″ to 4″ FMC is determined by using the tables in
Chapter 9 of the Code. For 3/8″ FMC, the number of
conductors is indicated in Table 348.22 of the Code.
NOTE
Conduit sizing is discussed in Chapter 6 of this text.
Liquidtight flexible metal conduit (LFMC)
Liquidtight flexible metal conduit is identical to flexible
metal conduit except it has an outer plastic jacket that makes
it impervious to liquids. It is manufactured in sizes from 3/8″
to 4″ in diameter. The connectors are watertight as well.
Requirements for number of conductors, bends
permitted, and supporting liquidtight metal flex are the same