Branch Circuits & Feeders第 5 / 120 题
A 120-volt circuit carries 20 amperes through 12 AWG copper (6,530 circular mils) to a load 100 feet away. Using K = 12.9, what is the approximate voltage drop?
a.10.5 volts
b.3.9 volts
c.5.2 volts
d.7.9 volts
解析
For a single-phase circuit, VD = (2 x K x I x L) / CM = (2 x 12.9 x 20 x 100) / 6,530 = 51,600 / 6,530, or about 7.9 volts. The 3.9-volt answer forgets that current travels out and back, so it omits the factor of 2; 5.2 volts and 10.5 volts do not correspond to any correct combination of the formula terms.
法律依据: 2023 NEC Chapter 9, Table 8免费刷完整 120 道题库 — 无需注册。
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