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 seemed to stop growing there, remaining at about 12 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 used to be very verbose; in the 2014 NEC it took up nearly 3/4 of a page. I said at that time 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. The 2017 NEC did, indeed, boil it down to that. And the 2020 NEC kept the revison intact.
- 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 as in 2014 with the PLFF definition question, we're confronted with so much text that a concise definition seems to be 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 (O)] 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 crimping 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. This strikes me as one of those instances where the NEC requirement isn't written to prevent electricians from doing something but to back them up when they refuse to do it. In four decades of working in or around the electrical industry, I've concluded that very few electricians will do work that is sloppy or stupid. But they are often expected to do work that is sloppy or stupid to "save" time or money. And as they say, "That's when the fight begins."
- 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 and make sure your cable supports are steel..
- For quite some time, there was some controversy over abandoned cables because 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. And it's yet another of those things I was talking about in Point 7 above.
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.