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Design practice questions

25 questions from the solar pv fundamentals practice test.

Design practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Which conductor types are permitted for exposed single-conductor PV source circuit wiring run within the array outdoors?

  1. THHN or THWN
  2. NM cable or UF cable
  3. XHHW or TW
  4. PV wire or USE-2
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D. PV wire or USE-2

Exposed array wiring must stand up to sunlight, heat and moisture, so listed PV wire (PV cable) or sunlight-resistant USE-2 is used. THHN is a building wire meant for raceways and is not rated for exposed use on a roof.

Reference: NEC 2023, 690.31(C)(1)

How should electrical terminals and racking fasteners be tightened?

  1. As tight as possible with the largest available wrench
  2. To the manufacturer's torque value, with a calibrated tool
  3. Until hand tight, to allow for later thermal expansion
  4. To a single standard value used for every fastener size
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B. To the manufacturer's torque value, with a calibrated tool

Terminals and structural fasteners are tightened to the values the manufacturer specifies using a calibrated torque tool; loose connections overheat and overtightened ones are damaged. Maximum force is not the goal.

Reference: NEC 2023, 110.14(D); manufacturer installation instructions

Why is an air gap normally left between roof-mounted modules and the roof surface?

  1. Air flow dries the wiring, which raises its ampacity
  2. The gap raises the array so it receives more sunlight
  3. Air flow cools the modules, which improves their output
  4. The gap lets the roof flex freely under heavy snow load
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C. Air flow cools the modules, which improves their output

Module voltage and power drop as cell temperature rises, so letting air move behind the modules keeps them cooler and more productive. Modules mounted tight to the roof run noticeably hotter.

Reference: Mechanical design: module cooling

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