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Old 01-22-2008, 08:58 AM   #1
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Residential Smoke Detector Wiring

I am in the process of adding smoke detectors in our 1911 house that currently has none. This is being done in conjunction with a whole-house re-wiring job that I'm performing (slowly) myself.

I have consulted the IBC regarding required locations. Next, I consulted the NEC to see what they have to say about any special wiring requirments. Article 760 deals with Fire Alarm Systems and after reading this (through a lot of yawning), it seems like this is more geared toward a comprehensive (commercial?) fire alarm and signaling system. Either way, I have a few general questions about wiring:

1. The new construction condominium that we lived in for 6 years in Chicago had smoke detectors that derived their power from overhead lighting circuits. I know that this building was inspected so I am assuming that as long as there are no disconnecting means (other than the OPD) in the supply wiring, using a lighting circuit for power is OK. IMO, from a reliability standpoint, I would think that this would be preferable to a recept. circuit.

2. I understand that all detectors are to be interconnected such that in the event that a single unit goes into alarm, all will sound. In my condo, the electrician had run an additional yellow wire between the detectors for this purpose. This brings up a few questions: 1. Since all detectors are interconnected via this signaling wire, do they all need to share the same power source? 2. I think that some of the newer units can communicate wirelessly. Are these allowed to be used without a hardwired interconnection means or is this dependent on the municipality?



Well, now, there's what's right and what's right and never the twain shall meet.
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Old 01-22-2008, 10:14 AM   #2
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The NEC doesnt list requirements for dwelling unit smoke alarms. That information is listed in the National Firecode Book.

1. All the smokes have to be interconnected on the same circuit via a 3 wire cable (14-3) and if you are completely rewiring the house I believe the smokes are required to be on an arc fault combination type breaker to bring it up to code. I dont see a problem with putting them on a lighting circuit as long as they're hardwired and not switched. I usually put them on one of the bedroom circuits.

2.a)yes b)If it is not hardwired I dont think it will meet code, if your doing an entire house re-wire like you say, I would just do a hardwire installation. It is safer and more reliable.


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Old 01-22-2008, 11:14 AM   #3
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Here is pretty much the latest on smokes

NFPA 72 and various building codes have different specific requirements.

Here is a rough summary of what Chapter 11 of NFPA 72 (specifically 11.5.1) requires:
  • One in each bedroom (to wake people up).
  • One on each level, including basement.
  • A smoke in a basement shall be on the ceiling, near the entry to the stairs.
  • One outside each sleeping area, within 21 feet of the door to any sleeping area. If the hallway is closed off from the sleeping and living areas by doors, then smokes are required on both the living and hallway sides of the door.
  • When a door is installed in a stairway, smoke rising up the stairwell cannot be obstructed from a detector by the door.
  • One in the living area of a guest suite.
  • When a given level of a living area is 1000 sq.ft. or greater, one is required for every 500sq.ft. of floor area for that space, no greater than 30 ft apart.
  • If a ceiling on any level has an elevation change of 24", each elevation needs one. Example: Vaulted living room on same floor as 8' ceiling for back hall, den, laundry.
  • No closer than 3' to any cold air return or supply, or ceiling fan. Nuisance alarms due to dust attraction are common when this is done, and the sensitivity can diminish.
  • No closer than 4" and no farther than 3' to peak of vaulted ceiling. Smoke rolls in corners, bypassing detector.
  • No farther than 3' from peak of vaulted ceiling.
  • No closer than 4" from wall on a flat ceiling.
  • No closer than 4" from ceiling and no farther than 12", when wall mounted.
  • Ambient temperature cannot exceed 100 F, or below 40 F, as in attics and garages.
  • Interconnection of detectors is required.
  • Per NEC 210.12, AFCI protection required. Per NFPA 72 11.6.3(7), if the smoke is supplied by an AFCI, then battery backup is required. By 11.6.4(1), the smoke must audibly report a low battery condition.
  • The instruction booklet supplied with the smoke detector is required to be provided to the occupant. (72 11.8.4(1).)
  • Smokes should be replaced every ten years. (72 11.8.5(b).)
Many smoke detectors come with instructions that mirror NFPA 72's requirements, so they could also be considered a 110.3(B) listing issue, if NFPA 72 has not been adopted in your area.

This excerpt taken from George Stolz (Moderator) on the Mike Holt Code Forum
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