Michigan Electrical Journeyman Exam Preparation

Below is a small sample of our exam prep questions:

1. What would be the calculated minimum size feeder circuit conductors for Multiple Motors on the same feeder given: 230 volts three-phase, Design B
◦ Motor 1: 10 HP, nameplate rating of 24 A
◦ Motor 2: 2 HP, nameplate rating of 4.7 A
→ Step_1: Table 430.250 lists the FLC at 28 amperes, and 6.8 amperes respectively.
→ Step_2: 430.24, Multiple motors are calculated at 125% of the largest motor, in addition to the remaining motors FLC ratings. Calculate; 28 amperes x 1.25 = 35 A + 6.8 A = 41.8 amperes.
→ Step_3: Table 310.15(B)(16) slide down the THW (75 deg C) column to size up to 50 A, then slide to the left to size the 8 AWG feeder circuit conductors.

2. What is the maximum allowable ampacity of ten 12 AWG THHN current-carrying conductors installed in the same raceway?
◦ Step_1: Per Table 310.15(B)(16) lists 30 amperes.
◦ Step_2: Per Table 310.15(B)(3)(a) lists 10-20 Conductors at 50%.
◦ Step_3: Per Table 310.15(B)(2)(a) lists a correction factor for 86 deg F, 90 deg C wire at 1.00.
◦ Step_4: Calculate; 30 amperes x 0.50 x 1.00 = 15 A

3. Calculate the minimum size Schedule 40 PVC required to install four THHN conductors; 2 – 500 kcmil, 1 – 350 kcmil, 1 – #2 AWG?
◦ Step_1: Per Chapter 9, Table 5 sum the areas of the conductors, below:
→ 2 – 500 kcmil; 2 x 0.7073 = 1.4146
→ 1 – 350 kcmil; 1 x 0.5242 = 0.5242
→ 1 – #2 AWG; 1 x 0.1158 = 0.1158
Total area = 2.0546 sq.in.
◦ Step_2: use Chapter 9, Table 4, and slide down the “Over 2 Wires” column until you see at least 2.0546 sq.in., which is 2.907, which corresponds to a trade size 3 inch.

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