Table 310.15(B)(1) Ambient Temperature Correction Factors Based on 30°C (86°F)
For ambient temperatures other than 30°C (86°F), multiply
the ampacities specified in the ampacity tables by the appropriate
correction factor shown below.
Ambient Temperature
Temperature Rating of Conductor
Ambient Temperature (°F)
60°C
75°C
90°C
10 or less
1.29
1.20
1.15
50 or less
11-15
1.22
1.15
1.12
51-59
16-20
1.15
1.11
1.08
60-68
21-25
1.08
1.05
1.04
69-77
26-30
1.00
1.00
1.00
78-86
31-35
0.91
0.94
0.96
87-95
36-40
0.82
0.88
0.91
96-104
41-45
0.71
0.82
0.87
105-113 >
46-50
0.58
0.75
0.82
114-122
51-55
0.41
0.67
0.76
123-131
56-60
-
0.58
0.71
132-140
61-65
-
0.47
0.65
141-149
66-70
-
0.33
0.58
150-158
71-75
-
-
0.50
159-167
76-80
-
-
0.41
168-176
81-85
-
-
0.29
177-185
310.15(B)(2) Rooftop.
For raceways or cables exposed to direct sunlight on or above rooftops where
the distance above the roof to the bottom of the raceway or cable is less than
23 mm (7∕ 8 in.), a temperature adder of 33°C (60°F) shall be added to the outdoor
temperature to determine the applicable ambient temperature for application of the
correction factors in Table 310.15(B)(1) or Table 310.15(B)(2).
Exception: Type XHHW-2 insulated conductors shall not be subject to this ampacity
adjustment.
Informational Note: One source for the ambient temperatures in various locations
is the ASHRAE Handbook — Fundamentals. For Colorado, the temperature inside the conduit
in direct sunlight could reach up to 155 degrees.