Chapter 6 Conductors 99 Copyright Goodheart-Willcox Co., Inc. 6.5 Conduit Capacity Of the many methods of wiring used in com- mercial installations, conduit is used most frequently, either as the sole method or in conjunction with other systems. The required conduit size depends on the conductors to be routed. There are three factors involved when sizing conduit: • The allowable conduit fi ll (percentage) fi • The total cross-sectional area of the conductors • The number of conductors within the conduit. These three factors determine the conduit size. Several tables from Chapter 9 of the Code are needed to size conduit: • Table 1—Maximum allowable fill in fi conduit • Table 4—Total and allowable areas for different conduit types and sizes • Table 5—Conductor diameter and areas. Given the number and size of conductors, the conduit is sized using a two-step process. First, the total area of the conductors is calculated. Then, the conduit size is selected. 6.5.1 Area of Conductors Table 5 in Chapter 9 of the Code contains the cross-sectional areas for conductors. The table is organized by conductor type and conductor size. Determining the area of conductors is easy. First, find the type of conductor in the left col- fi umn, then find the size and read the area in the fi far right column. When you are determining the total area of all conductors in a conduit, repeat this process for each conductor to be contained in the conduit. Then, add the areas of all of the conductors together to determine the total con- ductor area. 6.5.2 Minimum Conduit Size Table 1 in Chapter 9 of the Code shows the allow- able percentage of conduit area that can be filled fi SAMPLE PROBLEM 6-7 Problem: One O 12 AWG THHN, one 10 AW WG THHN, and n d three 8 AWG THHN conductors r s are to be run ru through rigid metal conduit. . Deter- mine th t he total area of the conductors. Solution: u Use Table 5 to fi nd the c co nductor fi are r ea s. T Ta ble 5 Continued Approximate e Approximate Size Diameter r Area (AWG or Type kcmil) mm in. mm2 in.2 Type: RHH*, RHW*, RHW-2*, TH T HHN, THHW, THW, THW-2, TFN,F TFFN, THWN, N, THWN-2, XF, XFF RHH,* RHW,* 10 5.232 5 0.206 21.48 0.03333 RHW-2,* XF, XFF RHH*, RHW*, 8 8 6.756 0.266 35.87 0.05565 RHW-2* 2000 47.80 1.882 1795 2.78188 81 TFN, 18 2.134 0.084 3.548 0 0. 00550 TFFN 16 2.438 0.096 4.645 0.0072 14 2.819 0.111 6.258 58 0.0000970 THHN, THW WN , 12 3.302 0.130 8.581 .5 0.0133 12 THW H WN -2 10 4.166 0.164 13.61 3 0.0211 10 8 5.486 0.216 23.61 2 0.0366 8 6 6.452 0.254 32.71 0.0507 4 8.230 0.324 53.16 0.0824 3 8.941 0.352 2 62.77 0.0973 2 9.754 0.384 84 74.71 0.1158 1 11.33 0.446 .4 100.8 0.1562 4 166 0 16 4 13 6 1 0 0 0 Copyright © 2016 NFPA 12 AWG THHN: 1 × 0.0133 0 in2 = 0.0133 in2 10 AWG THHN: 1 × 0.0211 0 in2 = 0.0211 in2 8 AWG THHN: 3 × × 0.0366 in2 = 0.1098 in2 Adding the areas together... t 0.0133 + 0.02 21 1 + 0.1098 = 0.1442 in2 The total area a of the conductors is 0.1442 in2.