Use and Care Guide

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E-517
Conduit & Fittings — Carlon
®
PVC Elbows, Conduit & Fittings
Expansion and Contraction
Temperature Considerations for Rigid Non-Metallic Conduit
Compensation for Linear Expansion
Like all construction materials, PVC will expand or contract with variations
in temperatures. The coefficient of linear expansion in PVC conduit is 3.38
x 10
-5
in./in./°F as compared to 1.2 x 10
-5
for aluminum and .6 x 10
-5
for
steel An expansion fitting is needed whenever the change in length due to
temperature variation will be
1
⁄4 in. or greater per 352.44 of the NEC.
Add 30° F to the estimated temperature range when conduit is installed in
direct sunlight to allow for radiant heating.
An expansion fitting consists of two sections, one telescoping inside
another. When installing expansion fittings, alignment of piston and barrel
is important. Be sure to mount expansion fitting level for best performance.
For a vertical run, the expansion fitting must be installed close to the top of
the run with the barrel jointing down, in order that rain water does not run
into the opening. The lower end of the conduit run must be secured at the
bottom so that any length change due to temperature variation will result in
an upward movement.
Determine the Piston Opening
The expansion joint must be installed to allow both expansion and
contraction of the conduit run. The correct piston opening for any
installation condition should use the following formula:
Example
380 ft. cf conduit is to be installed on the outside of a building exposed to
the sun in a single straight run. It is expected that the conduit will vary in
temperature from O° F in the winter to 140° F in the summer (this includes
the 30° F for radiant heating from the sun.) The installation is to be made
at a conduit temperature of 90° F. From this table, a 140° F temperature
change will cause a 5.7 in. length change in 100 ft. of conduit. The total
change for this example is 5.7" x 3.8 = 21.67" which should be rounded
to 22". The number of expansion fittings will be 22" x fitting range (4" for
Carlon trade sizes
1
⁄2" through 1
1
⁄2", and 8" for sizes 2" through 6".) If the
E945D fitting is used, the number will be 22" x 4 = 5.50 which should be
rounded to 6. The fitting should be placed at 62 ft. intervals (380 x 6). the
proper piston setting at the time of installation is calculated as explained
above.
Insert the piston into the barrel to the maximum depth. Place a mark on the
piston at the end of the barrel. To properly set the piston, pull the piston out of
the barrel to correspond to the 2.1 in. calculated above. See drawing at left.
Summary
1. Anticipate expansion and contraction of PVC conduit in above ground,
exposed installation.
2. Use an expansion fitting when length change due to temperature
variation will be
1
⁄4" or greater per 352.44 of the NEC
®
.
3. PVC conduit expands 4.1" for each 100 feet of run and a 100° F
temperature change.
4. Align expansion fitting with the conduit run to prevent binding.
5. Follow the instructions to set the piston opening.
6. Rigidly fix the outer barrel of the expansion fitting so it cannot move.
Mount the conduit connected to the piston loosely enough to allow the
conduit to move as the temperature changes.
Expansion Characteristics of PVC Rigid Non-Metallic Conduit
Coefficient of Thermal Expansion = 3.38 x 10
-5
in./in./°F
TEMPERATURE
CHANGE IN
DEGREES F
LENGTH CHANGE IN
INCHES PER 100 FT.
OF PVC CONDUIT
TEMPERATURE
CHANGE IN
DEGREES F
LENGTH CHANGE IN
INCHES PER 100 FT.
OF PVC CONDUIT
TEMPERATURE
CHANGE IN
DEGREES F
LENGTH CHANGE IN
INCHES PER 100 FT.
OF PVC CONDUIT
TEMPERATURE
CHANGE IN
DEGREES F
LENGTH CHANGE IN
INCHES PER 100 FT.
OF PVC CONDUIT
5 .2 55 2.2 105 4.2 155 6.3
10 .4 60 2.4 110 4.5 160 6.5
15 .6 65 2.6 115 4.7 165 6.7
20 .8 70 2.8 120 4.9 170 6.9
25 1.0 75 3.0 125 5.1 175 7.1
30 1.2 80 3.2 130 5.3 180 7.3
35 1.4 85 3.4 135 5.5 185 7.5
40 1.6 90 3.6 140 5.7 190 7.7
45 1.8 95 3.8 145 5.9 195 7.9
50 2.0 100 4.0 150 6.1 200 8.1
0 =
[
T max -T installed
]
E
∆T
0 =
[
140-90
]
4.0=1.4 in.
140
Piston Opening
Maximum Depth
Mark
Solvent WeldSolvent Weld
Pipe strap should
be anchored tightly
to barrel
Pipe strap mounted
loosely to allow
movement.
NEC and National Electrical Code are registered trademarks
of the National Fire Protection Association, Inc.
Technical Information