Fire & Life Safety: Pop Quiz on NEC Wiring Methods
Whether you are practicing for a fire alarm exam or just want to test yourself on wiring methods, try this quiz to test your knowledge of how to locate rules of adopted codes and standards. This test references the 2011 edition of the National Electrical Code.
You can answer these eight questions and then check your work in the “answers” section below them. Anyone can guess, but a pro both knows the rules and knows where those rules are located.
Question #1: If you fish NAC and IDC circuits from the basement of a two family condo, up to the second floor, do you need to use FPLP-rated cable?
Question #2: Your technician has extended the SLC loop from a manual pull box to add a smoke detector by drilling into the wall cavity above the ceiling grid, then, he fished the wire down about five feet to the manual pull box located in the same room now protected with the new addressable smoke detector. The technician didn’t make a hole through the fire-rated wall. Is he finished?
Question #3: An electrical contractor showed you some metal clips that push down onto the top of the T-bar used to hold the tiles on a suspended ceiling. These clips were made to hold the cables for his low-voltage track lighting system about four inches above the ceiling grid. Can you use these clips to keep the alarm cables off the tiles for the fire alarm system wiring?
Question #4: Your technician shows you his neat work with all the many cables bundled tightly together using nylon zip ties. You notice that not all the cables are actually running through the support rings, which are full; however, all cables are securely bundled and neat looking. What part of the NEC do you show him indicating the error he has made?
Question #5: Why is it that I seem to run across equipment and devices that don’t seem to meet the NEC requirements as they relate to fire alarm systems? Do the dry-wall boxes that have no backs, mud rings, and similar plaster rings I see being used by other low voltage contractors meet the NEC?
Question #6: Your technician points out that the mechanical contractor has tie-wrapped a four-conductor thermostat cable to the electrical conduit containing the 120 volt AC wiring powering an HVAC unit and wants to “say something” about it to him. Is the technician correct about this being a rather basic NEC violation?
Question #7: Can FPL wiring exit from a section of EMT or must it only exit through a box having a wire clamp and bushing?
Question #8: Your technician used a 7/8-inch paddle bit to drill through about 25 2x4 studs in order to run FPL wiring to a manual pull box and horn-strobe. Now he plans to install metal plates on about every other stud to protect the wiring from damage from nails and drywall screws. I thought the rule would apply to every stud, not half of them. The inspector says it should have been a smaller hole. What’s that have to do with every other stud needing a steel protective plate?
The Answers
#1: No. NEC section 760.154 states that the cable you use may be type FPL — “(3) Type FPL cable shall be permitted in one- and two family dwellings.” Save the FPLR for running wiring exposed (no conduit) in commercial buildings having more than two floors.
#2: The NEC tries to limit the spread of fire and products of combustion in section 300.21. It states, in part, that “openings around electrical penetrations into or through fire-resistant-rated walls, partitions, floors or ceilings shall be fire-stopped using approved methods to maintain the fire resistance rating.” By putting a hole in the fire-rated wall — even though it is hidden and doesn’t go all the way through the wall — it must be firestopped “using approved methods” to return the original fire resistance rating given to that partition.
#3: Your electrician is installing a listed product according to the manufacturer’s documented instructions. You are not installing a product designed and tested as a system — you are providing wiring. Wiring is installed according to section 300.11 of the NEC, which states “cables and raceways shall not be supported by ceiling grids.” It does provide an exception that states “the ceiling support system shall be permitted to support wiring and equipment that have been tested as part of the fire-rated assembly.” The use of these clips doesn’t fit the exception.
#4: Show him NEC Section 300.11 Securing and Supporting — “cable wiring methods shall not be used as a means of support for other cables, raceways or non-electrical equipment.” Once the existing support rings are full, additional supports are needed.
#5: They meet NEC requirements because the rule for fire alarm system terminations and boxes are not found elsewhere in the NEC for other systems. According to 760.130 Wiring Methods and Materials on Load Side of the PLFA Power Source – (B) PLFA Wiring Methods and Materials, “cable splices or terminations shall be made in listed fittings, boxes, enclosures, fire alarm devices, or utilization equipment.”
#6. It isn’t a violation for the mechanical contractor’s electrician to do this, but it would be a violation for your fire alarm technician (and he’ll make your company look bad.) This is because NEC section 760.143 specifically states that “power-limited fire alarm circuit conductors shall not be strapped, taped or attached by any means to the exterior of any conduit or other raceway as a means of support.” No exceptions are shown here for fire alarm wiring, but section 300.11 under “Securing and Supporting” has an exception to our fire alarm rule. The HVAC contractor will be exonerated by “300.11...(2) Where the raceway contains power supply conductors for electrically controlled equipment and is used to support Class 2 circuit conductors or cables that are solely for the purpose of connection to the equipment control circuits.” Employer 101: Teach all your technicians to bring their questions and issues to their supervisor.
#7: A box is not required if a bushing is used at the end of the conduit where the wires exit. According to NEC 760.3 (K) Bushing, “a bushing shall be installed where cables emerge from raceway used for mechanical support or protection in accordance with 300.15(C).” Then section 300.15 – Boxes, Conduit Bodies or Fittings – Where Required – (C) Protection states “a box or conduit body shall not be required where cables enter or exit from conduit or tubing that is used to provide cable support or protection against physical damage. A fitting shall be provided on the end(s) of the conduit or tubing to protect the cable from abrasion.”
#8: Wiring must be protected if the edge of the bored hole is within 1 ¼ inch from the edge of a wood member. A 2x4 is actually only 3½ inches wide. To not be closer than 1¼ from each edge, the bit should be no larger than 7/8 inch. Even though your tech used a 7/8 bit, he was in the dead center of the stud only about half the time, meaning that about half the studs have the hole within less than 1¼ inch from the edge. The inspector is right, either drill smaller holes somewhere near the center of the stud, or 7/8 inch holes precisely in the center next time. The inspector seems familiar with NEC section 300.4 “Protection Against Physical Damage – (A) Cables and Raceways Through Wood Members – (1) Bored Holes: “In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less than 32 mm (1 ¼ in.) from the nearest edge of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate(s) or bushing(s), at least 1.6 mm (1⁄16 in.) thick, and of appropriate length and width installed to cover the area of the wiring.”
Greg Kessinger is SD&I’s fire alarm and codes expert and a regular contributor. Email him your fire & life safety questions at [email protected].
