94 Modern Commercial Wiring Copyright Goodheart-Willcox Co., Inc. Ambient Temperature (°C) ° 90°C ° Temperature Rating of Conductor Ambient Temperature (°F) ° Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30°C ° (86°F)° For ambient temperatures other than 30°C ° (86°F), ° multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below. 10 or less 11–15 16–20 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 61–65 66–70 71–75 76–80 81–85 1.29 1.22 1.15 1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — — — — — 1.20 1.15 1.11 1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.47 0.33 — — — 1.15 1.12 1.08 1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.65 0.58 0.50 0.41 0.29 50 or less 51–59 60–68 69–77 78–86 87–95 96–104 105–113 114–122 123–131 132–140 141–149 150–158 159–167 168–176 177–185 Copyright © 2016 NFPA Figure 6-8. Temperature correction factors are listed in Table 310.15(B)(2)(a). Multiply the allowable ampacity at the standard temperature by the correction factor. Conductors installed close together, as in a raceway, are exposed to heat generated by the surrounding cables. This heat is not readily dis- sipated because the air in a conduit is fairly still. Section 310.15(B)(3)(a) includes adjustment fac- tors for more than three conductors in a raceway, Figure 6-9. Multiplying this correction factor by the allowable ampacity for three or less conduc- tors obtains the actual allowable ampacity. In the Code, this correction factor is expressed as a percentage, rather than a decimal value. Goodheart-Willcox Publisher Figure 6-9. Allowable ampacity is reduced when a raceway or cable contains more than three current- carrying conductors. Ampacity Adjustment Factors Number of Current- Carrying Conductors or s Adjustment Factor 4 to 6 0.80 7 7 to to 9 0.70 10 to 20 0.50 21 to 30 0.45 5 31 to 40 0.40 41 and above 0.35