Chapter 6 Conductors 95 Copyright Goodheart-Willcox Co., Inc. SAMPLE PROBLEM 6-4 Problem: ob Find the maximum allowable ampacity for six 1 1 AWG THW copper conductors in a single con o nd uit installed along the ceiling of a boiler room with an ambient a temperature averaging 125°F (52°C). Solution: So First, find the unmodified fi allowable ampacity from f fi Table 310.15(B)(16). Size AWG or kcmil Percent of Values in Table 310.15(B)(16) through Table 310.15(B)(19) as Adjusted for Ambient Temperature if Necessary Number of Conductors1 4–6 7–9 10–20 21–30 31–40 41 and above 80 70 50 45 40 35 1Number of conductors is the total number of conductors in the r ra ce- way or cable adjusted in accordance with 310.15(B)(5) and (6). ). Table Ta 310.15(B)(3)(a) Adjustment Factors for More Than T Th ree Current-Carrying Conductors in a Raceway or Cable Table 310.15(B)(16) (formally Table 310.16) Allowable Ampacities s of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C ° Through 90°C ° (140°F ° Through 194°F), ° Not Mor re than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature T of 30°C ° (86°F)° Temperature Rating of Cond duc tor [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 IS, FEP, FEPB, MI, RHH, RH Types TBS, SA, SIS, RHW-2, THHN, HN THHN, THHW, Types RHW, THHW, THW W- 2, Types RHW, THW-2, THWN-2, THHW, THW, THWN-2, USE-2, -2 XHH, THW, THHW, THW, RHH, RHW-2, USE-2, Types TW, THWN, XHHW, XHHW, XHHW-2, HH Types TW, THWN, XHHW, XHH, XHHW, Size AWG UF USE, ZW ZW-2 -2 UF USE XHHW-2, ZW-2 or kcmil COPPE ALUMINUM OR COPPER-CLAD ALUMINUM C OPPER 18 — — 14 — — — — — 16 — — 18 — — — — — — 14** 15 20 25 — — — — — 0 12** 20 25 30 15 20 25 1 12 ** 5 10** 30 35 40 25 30 35 10** 5 8 40 50 55 35 40 45 8 0 6 55 65 75 40 50 55 6 5 4 70 85 95 55 65 75 4 5 3 85 100 115 65 75 85 3 0 2 95 115 130 75 90 100 2 5 5 5 1 110 130 145 85 100 115 1 1 13 110 1/0 125 150 170 100 120 135 1/0 Copyright © 2016 NFPA For 1 AWG THW H copper conductors, the allowable ampacity is 130 amps. p Then, determine the correc- tion factors: : Temperature Correction Factor (125°F) = 0.67 No. of Conductors Correction Factor (6) = 0.80 0 By mult ti plying the unmodified allowable ampacity by the two cor o rr ection factors, the modified fi allow- fi able am mp acity is obtained: 130 amps × 0.67 × 0.80 = 70 amps