Chapter 6 Conductors 93 Copyright Goodheart-Willcox Co., Inc. 6.3.1 Ampacity Correction Factors The allowable ampacities listed in Tables 310.15(B)(16) through 310.15(B)(19) are only applicable for a specific number of conduc- fi tors and a specifi ambient temperature: fic • one conductor in Tables 310.15(B)(17) and 310.15(B)(19) • three conductors or less in Tables 310.15(B)(16) and 310.15(B)(18) • 86°F (30°C) ambient temperature in Tables 310.15(B)(16) and 310.15(B)(17) • 104°F (40°C) ambient temperature in Tables 310.15(B)(18) and 310.15(B)(19). When there are more than three conduc- tors in a raceway or the ambient temperature differs from the table values, corrections must be made. Table 310.15(B)(2)(a) contains temperature correction factors, Figure 6-8. Ambient tem- peratures are listed on both sides of the fac- tors: Celsius on the left and Fahrenheit on the right. The correction factor is multiplied by the allowable ampacity from the table to determine the allowable ampacity for a different ambient temperature. The ampacities of different conductor types vary differently with temperature change. Therefore, each type of conductor has unique temperature corrections. As the ambient tem- perature increases, the ampacity of the conduc- tor is reduced. SAMPLE PROBLEM 6-3 Problem: Three aluminum type THWN con nd uctors have been specified to carry 65 amps throug gh rigid fi non-metallic conduit. What size conductor rs are needed? Solution: Looking in the aluminum THWN W column of Table 310.15(B)(16), 65 amps is found in the e 4 AWG row. Therefore, the 4 AWG aluminum THWN W conductors are the smallest conductors allowed. Table 310.15(B)(16) (formerly Table 310.16) Allo ow able Ampacities of Insulated Conductors Rated Up to and Includi d in g 2000 Volts, 60°C ° Through 90°C ° (140°F ° Through 1 19 4°F), ° Not More than Three Current-Carrying Conductors in Race ew ay, Cable, or Earth (Directly Buried), Based on Ambient Temperature em of 30°C ° (86°F)*° Temperature ur Rating of Conductor [See Table 310.104(A).] 60°C 75°C 90°C 60°C 75°C ° 90°C (140°F) (167°F) (194°F) (140°F) (167°F) (194°F)° Types TBS, SA, SIS, F FE P, FEPB, MI, RHH, Types TBS, SA, SIS, S RHW-2, THHN, THHN, THHW W, Types RHW, THHW, THW-2, Types RHW, THW-2, THWN N-2, THHW, THW, THWN-2, USE-2, XHH, THHW, THW, RHH, RHW-2, U USE -2, Types TW, THWN, XHHW, XHHW, XHHW-2, Types TW, THWN, XHHW, XHH, XHHW, HW THWN, UF USE, ZW ZW-2 UF USE XHHW-2, ZW W- 2 COPPER PE ALUMINUM OR COPPER-CLAD ALUMIN NU M A LUMINUM 18 — — 14 — — — — 16 — — 18 — — — — — 14** 15 20 25 — — — — — 12** 20 25 30 15 20 2 25 12** 10** 30 35 40 25 30 35 10** 8 40 50 55 35 40 45 8 6 55 65 75 40 50 55 6 95 55 65 75 4 65 4 70 85 5 3 85 100 0 0 115 65 75 85 3 2 95 115 1 130 75 90 100 2 Size AWG or kcmil Size AWG or k il 95 55 70 85 — — — 20 30 40 50 50 50 4 Copyright © 2016 NFPA