National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 760, Fire Alarm Systems, Part 1
Article 760 is one of the longer Articles in the NEC. And with the 2014 edition of the NEC, it got even longer. It now runs almost 12 full pages.
- Two key definitions to understand and differentiate are those of "power-limited fire alarm circuits" (PLFA) and "non-power-limited fire alarm circuits (NPLFA). The requirements are similar in many respects but very different in other respects.
- A PLFA is one that's powered by a source which complies with 760.121 [760.2]. But what does this mean? Section 121 takes up nearly 3/4 of a page, so there's not a concise definition. But you can boil it down to the fact that the power supply is a Class 3 transformer or Class 3 power supply. If listed equipment is marked to identify an integral power source as PLFA, that also means you have a PLFA circuit.
- You might think a non-PLFA means "everything else." In real practice, that is correct and thus the language positioning PLFA vs. non-PLFA. But it doesn't mean any old power source, either. A non-PLFA source must meet the requirements of 760.41 and 760.43. Again, we must ask, "What does that mean?" And again, we're confronted with so much text that a concise definition is precluded. But again, we can boil it down. Basically, the power supply must comply with the requirements of Chapters 1 through 4. It's not that you have to go through those line by line looking for specfics, but that your installation is expected to meet Code. So if it's not a Class 3 power supply but otherwise does meet Code, you can use it to power your fire alarm circuit. That usage will, however, bring about additional requirements in Article 760. We'll address those in this series.
- The Code-Making Panel (CMP) for Article 760 wanted to stress the fact that this Article generally over-rides Article 300 requirements. The text says, "Only those sections of article 300 referenced in this Article shall apply to fire alarm systems." [760.3] Just to refresh your memory, Article 300 presents the general requirements for wiring methods and materials.
- Section 3 of this Article also presents a list of requirements [(A) through (K)] that all fire alarm circuits and equipment must comply with. None of these should be particularly surprising, but make sure you don't gloss over them.
- Throughout the NEC, we find requirements for the mechanical execution of work. For all installations, the installation must be done in a neat and workmanlike manner; for fire alarm circuits, this is repeated in 760.24(A). That same subsection tells you not to damage the cable by doing something stupid like cramping the cable with cable ties or staples (just not in those words, but that's the idea). A professional installer should not need to be told this, yet many installations are done with just such violations even though the NEC explcitly bans specific methods of stupidly damaging the cables.
- If you use Circuit Integrity (CI) cable (Article 725],follow the support requirements listed in 760.24(B). For starters, support it every two feet or less.
- There was some controversy over abandoned cables, since requirements were made more stringent among the BICSI crowd in their standards and in their training. Certified installers would go into a job and be confronted with a bird's nest of cables that weren't still used but were still energized. Often, no cabling was labeled and drawings weren't updated. Because these folks had this crazy idea that fire alarm systems (and other communication systems) should actually be reliable, they'd clean up this mess, document everything properly, and bill the client. But they didn't have NEC requirements that mandated this work. So language was added to the NEC. That ended the controversy.
Yes, you can leave abandoned cables in place; you don't have to actually pull them out of raceway, etc. But you have to remove the accessible portion (that is, get rid of what you can get to, so it doesn't get confused with cables that are being used) [760.25]. Cables that aren't used but might be used some day just need to be marked as such.
- Related to what we just looked at in point 9, all of the circuits must be properly identified. The identification must be made at the terminal and junction locations [760.30]. The idea is to prevent unintentional signals on fire alarm system circuits during testing and servicing of other systems.
Don't skimp here and try to do this with handwritten numbers on tape or with those roll-on stickers of letters and numbers. Not only do those methods violate "neat and workmanlike" execution, the first one (and probably the second one) isn't durable. Both are prone to error in reading, too. Use a professional cable marking system that makes quality labels. It is amazing at how much better an installation looks when using such a system, plus the work actually goes faster.
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Learn more about:
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.