National Electrical Code Explanations
Based on the 2020 NEC
National Electrical Code Tips: Article 760, Fire Alarm Systems, Part 3
- If your alarm circuit is a Non Power Limited Fire Alarm circuit (NPLFA), then unlike the Power Limited Fire Alarm circuit (NPLFA) it's basically a Chapter 3 wiring job [760.46]..
- You can run Class 1 and NPLFA in the same raceway [760.48(A)].
- You can run power supply and NPLFA circuit conductors in the same raceway too, but only if they connect to the same equipment [760.48(B)].
- You can't use aluminum conductors for fire alarm circuits [760.49(A)], and the conductors you do use must be rated at 600V or more [760.49(B)]. Alunimum conductors have a higher impedance than copper conductors (it's a function of the difference in the electron shells of aluminum versus copper) and run hotter. While the NEC permits aluminum conductors in many types of applications, it almost always is better to use copper.
- You determine the raceway fill per 300.17 [760.51(A) and (B)].
- Multiconductor NPLFA cables have so many requirements attached to them, the requirements take up 3/4 of a page [760.53]. Before considering such a wiring method, read this subsection carefully.
- The requirements for Power Limited Fire Alarm (PLFA) circuits take up nearly twice as much room in the NEC as those for NPLFA circuits. That isn't because the CMP just decided to be verbose or something. PLFA necessarily have tighter restrictions on the kinds of cables you can use and how you install them.
- A PLFA power source must be one of three things: Listed PFLA or Class 3 transformer, listged PLFA or class 3 power supply, or listed equipment marked to identify the PLFA source [760.121].
- The branch circuit supplying this equipment cannot supply other loads [760.121(B)]. Also, the OCPD for that circuit must have its location clearly indicated at the fire alarm control unit.
- Ensure any plainly visible equipment supplying PLFA circuits is durably marked to indicate each circuit that's a PLFA circuit [760.124].
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- Appendix D contains examples that every NEC user should study.
Try your NEC moxy:
- Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
- Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
- When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
- Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
- Take our Code Quizzes.
Remember other applicable codes, rules, standards, and references:
- OSHA's electrical worker safety rules.
- IEEE standards.
- NETA standards.
- NFPA standards.
- International Codes (if applicable to the installation).
- State Codes (if the state has them).
- Local ordinances and permit requirements.
- Local fire codes.
- Manufacturer requirements or guidelines.
- Customer security requirements.
- Industry standards.
- Your company's own internal standards, practices, and procedures.
- Engineering drawing notes.
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