64 Modern Commercial Wiring
Copyright Goodheart-Willcox Co., Inc.
Figure 5-10. Many types of fittings are used with rigid metal conduit and IMC. The conduit support fittings are also used to support
cables. (RACO, Inc.)
Rigid and Intermediate Metal Conduit Fittings
Conduit Support Fittings
Conduit Clamp Hanger Nail-Up Strap Two Hole Strap One Hole Strap
Three Piece Coupling
Long Elbow Short Elbow Set Screw
Connector
Bushing Locknut Compression
Connector
Coupling
Figure 5-11. Conduit support and bending limitations for rigid metal conduit, IMC, EMT, and rigid nonmetallic conduit. A—Conduit
must be supported within 3′ of a box. The maximum distance between supports is 10′. B—The total number of bends in a conduit
must not exceed 360°. Here, the maximum number of bends have been made.
10′ Maximum
between
supports
3′ Maximum
between
box and
support
A
Total bends = 90° × 4 = 360° (maximum)
90°
90°
90°
90°
B
Intermediate metal conduit (IMC)
IMC has a thinner wall than rigid metal conduit, but
is nearly as strong. It is approximately 25% lighter than
rigid conduit and is less costly. IMC can be threaded and
reamed in the field.
This conduit has the same permitted uses as rigid
metal conduit. It is manufactured in sizes of 1/2″ to 4″.
IMC also serves as an excellent equipment ground.
Just like rigid metal conduit, IMC must be supported
every 10′ and within 3′ of every outlet and fitting. The
total number of bends in each run must be less than 360°.
Electrical metallic tubing (EMT)
EMT, or thinwall conduit, is about half as heavy as
rigid metal conduit. This is due to the fact that EMT has
a much thinner wall (about 60% less) than rigid metal