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Thread: Max number of wireless smoke detectors in a multi-family

  1. #1
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    Max number of wireless smoke detectors in a multi-family

    Quoting from a related (closed) thread on this website, "Had time so I found a copy of NFPA 72 2010 edition handbook. 29.8.2.2 which has the requirement of 18 initiating devices 12 of them smoke detectors if the system is not supervised. If the system is supervised you can have 64 devices w/42 being smoke detectors. In the handbook intent was for unsupervised systems there was no way to monitor the integrity of the interconnecting wiring so was limited to smaller systems"

    If monitoring the integrity of the interconnecting wiring was the reason for the limit, why does the same limit apply to wireless devices?

    My current need: A four-plex building (basement + 2 floors) needs 2 detectors in basement plus one in each floor plus 5 (one in each bed for 3-bedrooms plus two in common area) in each residential unit for a total of 24 detectors.

    Any suggestions on how to solve for the current need?
    Sam

  2. #2
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    Quote Originally Posted by veerasam View Post
    Quoting from a related (closed) thread on this website, "Had time so I found a copy of NFPA 72 2010 edition handbook. 29.8.2.2 which has the requirement of 18 initiating devices 12 of them smoke detectors if the system is not supervised. If the system is supervised you can have 64 devices w/42 being smoke detectors. In the handbook intent was for unsupervised systems there was no way to monitor the integrity of the interconnecting wiring so was limited to smaller systems"

    If monitoring the integrity of the interconnecting wiring was the reason for the limit, why does the same limit apply to wireless devices?

    My current need: A four-plex building (basement + 2 floors) needs 2 detectors in basement plus one in each floor plus 5 (one in each bed for 3-bedrooms plus two in common area) in each residential unit for a total of 24 detectors.

    Any suggestions on how to solve for the current need?
    Sam
    Do you need interconnection between occupancies? Might depend on structural rating between occupancies.

  3. #3
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    Interconnection between occupancies

    Quote Originally Posted by kwired View Post
    Do you need interconnection between occupancies? Might depend on structural rating between occupancies.
    Yes. The inspector asked "If a fire starts in a basement the how will the occupants know to get out?"
    I presume, he will also ask "If the fire starts in a first floor unit, how will a second floor unit occupant know to get out?"

  4. #4
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    Interconnection between occupancies

    Quote Originally Posted by kwired View Post
    Do you need interconnection between occupancies? Might depend on structural rating between occupancies.
    Yes. The inspector asked "If a fire starts in a basement. how will the occupants on first floor know to get out?"
    I presume he will also ask "If a fire starts in the first floor unit, how will the second floor unit occupant know to get out?"

  5. #5
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    Quote Originally Posted by kwired View Post
    Do you need interconnection between occupancies? Might depend on structural rating between occupancies.
    This is forbidden by code. You can't have toast burning in Unit A setting off alarms in Unit B.

  6. #6
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    Quote Originally Posted by gadfly56 View Post
    This is forbidden by code. You can't have toast burning in Unit A setting off alarms in Unit B.
    I kind of suspected that to be the case. Also expect there normally would be at least 1 hour finish between units required as well, maybe even 2 hour finish in some instances.

  7. #7
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    Quote Originally Posted by kwired View Post
    I kind of suspected that to be the case. Also expect there normally would be at least 1 hour finish between units required as well, maybe even 2 hour finish in some instances.
    The exception would be if you had a building-wide FACP covering the common areas and pull stations or water flow switches. Then you can put a notification appliance inside each unit that tells everyone to get out of Dodge. However, you're still not tripping on an alarm device in any dwelling unit.

  8. #8
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    Quote Originally Posted by gadfly56 View Post
    The exception would be if you had a building-wide FACP covering the common areas and pull stations or water flow switches. Then you can put a notification appliance inside each unit that tells everyone to get out of Dodge. However, you're still not tripping on an alarm device in any dwelling unit.
    Just to clarify the context: It is a 1920's building in original structure. No sprinklers. The building was re-plumbed and rewired in 2010 when they ran wiring for interconnected smokes. No one lives in basement (it has only a laundry area, electric water heaters and storage). Two floors are above basement. Each floor has two residential units (one on left half and one on right half of the floor).

  9. #9
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    Quote Originally Posted by kwired View Post
    Do you need interconnection between occupancies? Might depend on structural rating between occupancies.
    Yes. The inspector asked "If a fire starts in a basement. how will the occupants on first floor know to get out?"
    I presume he will also ask "If a fire starts in the first floor unit, how will the second floor unit occupant know to get out?"

  10. #10
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    I did a similar set up several years back. Here is how we set things up, and the inspector liked it.

    We used wireless alarms. Each apartment was set up with it's own digital ID. In the basement, (common area) we installed four alarms a few inches from each other, one for each apartment system. That way, an alarm in an apartment wouldn't set off the alarm in another apartment, but smoke in the common area would set off all of them.

    I think there are better wireless links now that would allow for a single multi channel unit in a common area.
    Cheers and Stay Safe,

    Marky the Sparky

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