Chapter 6 Conductors 97 Copyright Goodheart-Willcox Co., Inc. SAMPLE PROBLEM 6-5 Problem: b Determine the voltage drop on a 20-amp circuit h ha ving a length (one-way) of 170′, 10 AWG ′ THW H W stranded copper conductors, and a single-phase, 120-volt - power supply. Solution: o From Table 8 of Chapter 9, the resistance for 10 0 AWG stranded copper conductor (uncoated) is is 1.24 ohm/kFT. 18 18 16 16 14 14 12 12 10 10 8 8 1 7 1 7 1 7 1 7 1 7 1 7 — 0.39 — 0.49 — 0.62 — 0.78 — 0.98 — 1.23 1.02 1.16 6 1.2 .29 1.46 1 1.63 1.85 2.05 2.32 2.588 2.95 3.264 3.71 0.040 0.046 0.051 0.058 0.064 0.073 0.081 0.092 0.102 0.116 0.128 0.146 0.001 0.002 0.002 0.003 0.003 0.004 0.005 0.006 0.008 0.011 0.013 0.017 7.77 7.95 4.89 4.99 3.07 3.14 1.93 1.98 1.21 1.24 0.764 0.778 8.08 8.45 5.08 5.29 3.19 3.26 2.01 2.05 1.26 1.29 0.786 0.809 42.0 42.8 26.4 26.9 16.6 16.9 10.45 10.69 6.561 5 6. 6.6 79 4.125 4.204 12.8 13.1 8.05 8.21 1 5.06 .0 5 5.1 7 3.18 5 3.25 9 2.00 61 2.04 79 1.26 25 1.28 04 26.5 27.7 16.7 17.3 10.4 10.7 6.57 6.73 4.148 4.226 2.579 2.653 25.5 26.1 16.0 16.4 10.1 10.3 6.34 6.50 3.984 4.070 2.506 2.551 0.823 1.06 1.31 1.68 2.08 2.68 3.31 4.25 5.26 6.76 8.37 10.76 — 0.015 — 0.019 — 0.024 — 0.030 0 — — 0.038 .0 — 0.049 1620 1620 2580 2580 4110 4110 6530 6530 10380 10380 16510 16510 0.823 0.823 1.31 1.31 2.08 2.08 3.31 3.31 5.261 5.261 8.367 8.367 Table 8 Conductor Properties Area ohm/ km ohm/ kFT ohm/ kFT ohm/ km ohm/ kFT Uncoated Area Diameter r Diameter Stranding Copper Aluminum Copper Conductors Direct-Current Resistance at 75°C (167°F) Coated ohm/ km Circular mils Quantity mm in. mm2 in.2 mm2 Size (AWG or kcmil) i 7 0 98 2 95 0 116 0 011 4 070 6 7 0 0 38 10380 5 261 0 0 Copyriig ght © 2016 NFPA Using the equation presented in i the previous discussion: VD = 2 × × I × R __L ____ 1000 = 2 × 170′ A ____× _______hm/kF_T___o1.24×A20 _ 1000 = 8.4 V To determine the voltag ge drop as a percentage of the total voltage, divide the voltage ta drop by the total voltage: 8.4 __V _ 120 V = 0.07 _ V = 7% The Code recommends m a maximum 3% voltage drop. It would be advisable t to rewire this circuit using a No. 6 AWG copper pp conductor, which would reduce the voltage drop to an a ac ceptable level: VD = 2 2 × 170′ ____× _20______hm/kFT____o0.491×A_ 1000 = = 3.3 V Checking g the t voltage drop as a percentage of the total voltage: 3.3 V __V _ _ 120 0 V = 0.0275 _ V = 2.75% This s is acceptable.