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Suppose 3 interconnected smoke detectors on first floor. Standard wiring would run 14/2 to first, then 14/3 (with red wire for interconnecting) to second, then 14/3 to third. My question is whether this alternative wiring would be acceptable, especially considering all smoke detectors should alarm when any detects smoke.

Alternative wiring: 14/2 runs from breaker to a single junction box in the attic. Then three cables (14/3) run to each smoke detector from the junction box. All white wires would be connected in the junction box; same for black wires; same for red wires.

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  • This is down to the instructions for that particular product.
    – Solar Mike
    Sep 25 at 15:14
  • @VtC - Where is the OP asking for a product recommendation?
    – FreeMan
    Sep 27 at 13:03
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For typical interconnected smoke alarms, this is fine

For the typical hardwired interconnections found on North American smoke alarms, this is alright -- they don't care about the topology of the wiring, only that the interconnect wire connects the smoke detectors together.

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  • Just curious, which FACPs care about wiring topology?
    – DrSparks
    Sep 25 at 20:30
  • @DrSparks -- the OP is likely not aware of the distinction between "smoke detectors" that go with a FACP and "smoke alarms" that stand alone/are interconnected to each other only. Conventional smoke detectors (2-wire and 4-wire) generally do care about topology to provide supervision (can't T-tap traditional supervised contact-closure circuits), most addressable systems are fairly free-topology with their SLCs tho Sep 25 at 21:03
  • Gotcha. I've encountered those systems. They had a resistor at the end of the chain to complete the loop. Addressable systems are certainly preferred, simply for the ability to more accurately determine the location of a fire.
    – DrSparks
    Sep 25 at 21:21
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The hub and spoke topology not only is not prohibited by Code, but may be a more electrically sound design. Fewer points of failure and shorter overall runs of cable. It does, however, introduce a single point of failure and eliminate some redundancy, so it's a give and take situation.

Luckily, all hardwired smoke detectors come with a 9v battery backup and the system will annoy you for the rest of eternity until you replace the battery.

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