8.
You are preparing to pull in the wires from service equipment to a sub-panel through parallel conduits that you have already installed. It is a 400 ampere three phase four wire feeder, plus the equipment grounding conductor. Due to the distance, to accommodate voltage drop you have to increase your ungrounded conductors from 3/0 cu to #250 kcmil. What minimum size will your copper (cu) equipment grounding conductor need to be?
a. #1 al
b. #3 cu
c. #2/0 cu
d. #1 cu
250.122(B) requires the EGC to be increased proportionately to the ungrounded conductors. Table 250.122 gives the EGC size for a 400a feed to be a #3 cu wire. Ch. 9 Table 8 gives the conductor circular mil area, for a #3/0 - 167,800, a #3 - 52,620. To find the ratio of increase in conductor size: 250,000 kcmil / 167,800 = 1.49. Apply the ratio to the #3 area: 52,620 x 1.49 = 78,404. Ch.9 Table 8 - 78,404 is larger than a #2, but smaller than a #1.

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13.
In the circumstances described in the previous question, the breaker feeding the workshop is a 150A 240V 2 pole device. What is the minimum required size for the copper Equipment Grounding Conductor in THWN insulation?
a. #8 THWN
b. #6 THWN
c. #3 THWN
d. #1/0 THWN
Table 250.122 shows a #6 required; 250.122(B) states that if the ungrounded conductors are increased in size, the ECG must be increased proportionately. Per Table 310.15(B)(16), #1/0 would be sufficient for 150A, that was increased to #350 kcmil. Ch. 9 Table 8 gives the circular mil area of #1/0 to be 105,600. To determine ratio: 350,000 ÷ 105,600 = 3.314. Circular mil area of #6 is 26,240, so applying the ratio = 26,240 x 3.314 = 86,959 circ. mils = #1/0.

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16.
You have 132 #14 THWN copper wires used for signaling in a Class 1 system, and 5 #12 THWN spare copper conductors. To get the wiring from the PLC to the machinery, you will use EMT conduit. What is the minimum size that the EMT will be required to be?
a. 2.5"
b. 2"
c. 4"
d. 3"
725.51(A) refers you to 300.17, which directs you to refer to the appropriate wiring method section of the NEC. In this case, you would use 358.22. Here it refers you to the appropriate Tables in Ch. 9, you will need to use Tables 1, 4, and 5 for the following numbers: #14 = 0.0097 circ. mil, #12 = 0.0133 circ. mil: 0.0097 x 132 = 1.2804, 0.0133 x 5 = 0.0665, 1.2804 + 0.0665 = 1.3469"^{2} . Table 4 shows 2.5" EMT to be the smallest available with sufficient area.

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