When are expansion fittings used, For conduit installed outdoors, Where installed inside buildings – Carlon Expansion Joints User Manual
Page 2: In./in./°f, Continued)
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When are expansion fittings used?
(continued)
Changes in conduit temperature outdoors can exceed 140°F
considering the heat of summer and cold of winter. This means a
100 foot run of conduit could change approximately 6 inches in
length between summer and winter. If not compensated for with
expansion fittings, this change in length can cause unsightly
conduit bowing, distorted boxes, or broken couplings or fittings.
The anticipated expansion and contraction for various lengths of
runs and temperature changes is given in Table 352.44 of the
National Electric Code
®
. (See Table below)
For conduit installed outdoors,
the maximum and minimum air temperature expected can be used to
calculate the range of expansion and contraction. Conduit installed out-
doors in direct sunlight will be considerably hotter than air temperature
during the day because of the absorption of the sun’s heat.
Expansion fittings should be installed to allow for the
anticipated temperature change. For direct sunlight
exposure, add 30°F to ambient air temperature change.
Where installed inside buildings,
the conduit temperature is the ambient air temperature plus the heat
contributed by the conductors inside the conduit. Generally, expansion
fittings are not required inside unless conduit is located in an area of
widely varying temperatures. Attics of buildings are areas
where temperature swings exceeding 100°F are common
and expansion fittings are required.
Expansion Characteristics of PVC Rigid Nonmetallic 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
0.2
55
2.2
105
4.2
155
6.3
10
0.4
60
2.4
110
4.5
160
6.5
15
0.6
65
2.6
115
4.7
165
6.7
20
0.8
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
1.8
100
4.1
150
6.1
200
8.1
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