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Power limited practice questions

26 questions from the low voltage and structured cabling practice test.

Power limited practice test

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

What this covers

Sample questions

Which NEC article covers the wiring of fire alarm systems, including power-limited fire alarm circuits?

  1. Article 725
  2. Article 640
  3. Article 760
  4. Article 820
Show the answer

C. Article 760

Fire alarm circuits have their own article, 760, with their own cable types such as FPL, FPLR and FPLP. Article 725 covers Class 2 and Class 3 circuits, which is where many people look first.

Reference: NEC 2023, Article 760

Which NEC article covers the installation of optical fibre cables?

  1. Article 725
  2. Article 800
  3. Article 830
  4. Article 770
Show the answer

D. Article 770

Optical fibre cables are covered by Article 770 even though they are often installed alongside the communications cables of Chapter 8. Article 800 contains the general requirements for communications systems.

Reference: NEC 2023, Article 770

Why are Class 2 circuits allowed less stringent wiring methods than power circuits?

  1. The cables used are always plenum rated and cannot burn at all
  2. The power source limits energy to levels low in fire and shock risk
  3. The circuits are always installed in grounded metal raceways
  4. The circuits only ever operate when the building is unoccupied
Show the answer

B. The power source limits energy to levels low in fire and shock risk

A Class 2 source is limited in voltage and power so that the circuit is considered safe from a fire-initiation standpoint and gives acceptable protection from shock. That limitation is in the listed power supply, not in the cable or raceway.

Reference: NEC 2023, Article 725, Class 2 circuit definition

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