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Thread: Smoke Alarms - Hardwired & Interconnecting

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    DoD Army bjferri's Avatar
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    Default Smoke Alarms - Hardwired & Interconnecting

    I want to retrofit my old house with hardwired interconnecting smoke alarms. I'd like to start of course in the basement where I have a dedicated old 12/2 metal conduit circuit that was used in the past but now has not home.

    The smoke alarms have a red, white, and black wire. The red is used for interconnections. I was told the circuit for smoke alarms can't be protected by a ground fault interruptor. Now I understand the metal conduit from my 12/2 is the ground.

    Does this mean I apply electric tape to the conduit before fastening it to the metal electric box to lose the ground fault interruption? This is all abstract to me what happens by cutting off the ground fault, or not...??? If someone can please explain I'll thank you in advance.

    Also, to interconnect one smoke alarm to the next, can I use the ground (since it is not being used) of the 12/2 for the red to interconnect? Or, do I have to use a 12/3? Or, something else?

    I don't know what else to ask...

    Thank you...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    To do this right, you need the smoke detectors on their own circuit (their own circuit breaker with nothing else attached), and 14/3 (12/3 is overkill but okay if you had it). A gfi circuit is an electronic circuit that monitors the hot and neutral and if there is an unbalance, it disconnects power. The safety ground is not a direct part of the operation of a gfi. GFCI circuits are required for kitchen counter outlets, bathroom outlets, outdoor outlets, and garage outlets.

    Basically, each of the detectors needs hot and neutral, and the third wire is used to allow them to be interconnected (so if one goes off, the others do, too). You should not use the ground wire for this, since if it made contact with a real ground anywhere, it would either damage the dectors or inhibit the interconnections to work...you need a dedicated, insulated wire for this.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DoD Army bjferri's Avatar
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    Right now I do have a dedicated 12/2 coming from the circuit box. This has the metal conduit since it is old and I was planning on using this to connect the first smoke alarm. Can I use this? If I can, how do I break the ground from the metal conduit when connecting into the metal 4" box?

    Are you suggesting 12/3 to interconnect?

    If you think I should start from scratch from the main circuit box I can. If I did would I use a 14/2 or 14/3?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You misunderstand what gfi is altogether. Ground is a safety thing, and you need to leave it intact - it can't be used as a current carrying or signal connector at all, so you can't 'break' that connection. The wire you have to the first detector is fine, since it only needs power. But, from that one to the rest, you need three dedicated wires: hot, neutral, and interconnect. You can't use the ground for that third connection. So, instead of running new wire everwhere, you only need it between the dectors. As noted previously, that circuit breaker or fuse should not supply power to any other device other than the detectors - you don't want something to trip that circuit and render your detectors inoperative.

    If the circuit breaker feeding this branch is a gfi breaker, then you need to change it out to a 'normal' one. The reason for this is that when a detector gets tripped, instead of all of the power going from the hot to the neutral lead, some of it goes through the signal wire. This causes an imbalance which trips the gfi circuit.

    When purchasing hardwired detectors, consider those with a battery backup. If you use a lithium battery, they can last the lifetime of the detector (which is recommended at a max of 10-years). If you have frequent or extended power outages, the battery may not last the full 10-years, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DoD Army bjferri's Avatar
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    Now I follow. Thanks.

    You say "The wire you have to the first detector is fine, since it only needs power. But, from that one to the rest, you need three dedicated wires: hot, neutral, and interconnect."

    Last question. If it's a 12/3 I use for the interconnections, what do I do with the ground wire?

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by jadnashua
    If the circuit breaker feeding this branch is a gfi breaker, then you need to change it out to a 'normal' one.
    The breaker that supplies the smokes is required by 210.12 to be an Arc-fault device.

    Quote Originally Posted by bjferri
    Now I follow. Thanks.

    You say "The wire you have to the first detector is fine, since it only needs power. But, from that one to the rest, you need three dedicated wires: hot, neutral, and interconnect."

    Last question. If it's a 12/3 I use for the interconnections, what do I do with the ground wire?
    Twist all the grounds together and push up in the box out of the way.

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    DoD Army bjferri's Avatar
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    Thanks regarding the ground. To clarify this. The main dedicated circuit I will have my first smoke alarm on will be using the metal conduit 12/2. The metal is the ground. I can't tuck this one away when I connect my first smoke alarm to the matel 4" box...the whole box will at that point be grounded. Is this okay? If not, how do I get around this.

    You say, "The breaker that supplies the smokes is required by 210.12 to be an Arc-fault device.", Are you saying I have to replace my old 20 amp circuit breaker with a new one that has arc fault protection?

  8. #8

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    The great AFCI debate...

    Article 210.12(B) states, "Dwelling Unit Bedroom Circuits. All 15 or 20A, 120V branch circuits that supply outlets in dwelling unit bedrooms must be AFCI-protected by a listed arc-fault circuit interrupter."

    Now smoke detectors aren't connected to outlets in the bedroom they're hardwired. Also circuits serving fire alarm alarm circuits are exempt from AFCI requirements per 760.21 and 760.41. Problem is NFPA 72 of the National Fire Alarm Code doesn't define interconnected smokes as fire alarms, but "regular" alarms. Yeah, that makes lots of sense.

    My personal opinion, which I realize might catch heat for, is put the fire alarm circuit on a standard breaker. This your life we're talking about.

    And yes, you have to use 3 conductor cable, plus ground. Never use a ground for anything but a ground. If you're local code requires 12/3 on 15A circuits like ours does in NYC, then run 12/3.

    Joe

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    Retired Defense Industry Engineer jadnashua's Avatar
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    To provide ground to the rest of the daisy chain, there is usually a threaded hole in the box that you can attach a pigtail to so you have something to tie the ground lead for the new x/3 cable going out from the first box. If you use metal boxes for the others, the inspector will probably want to see the ground connected to the box as well as the in/out wires even though the detector doesn't use the ground wire...this keeps the metal box safe if a wire gets pinched.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DoD Army bjferri's Avatar
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    So I do want to daisy chain the ground to the other smoke alarms and not tuck them out of the way? And an arc fault is not necessary?

    I thought a 12/3 goes on a 20 amp circiut. A 14/3 is 15 amps, right? I'm in NJ.

  11. #11

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    Yes that is correct.

    I would run that circuit in 14 guage using a 15 amp breaker. It is a low use circuit and doesn't require the heavier wire.

    Tom

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    DoD Army bjferri's Avatar
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    Thanks for all the help. You guys are the best source of information!

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by joe in queens
    The great AFCI debate...

    Article 210.12(B) states, "Dwelling Unit Bedroom Circuits. All 15 or 20A, 120V branch circuits that supply outlets in dwelling unit bedrooms must be AFCI-protected by a listed arc-fault circuit interrupter." Now smoke detectors aren't connected to outlets in the bedroom they're hardwired.
    look at the definition of outlet
    Outlet. A point on the wiring system at which current is taken to supply utilization equipment.
    I would think that the smoke alarm is a piece of equipment and that it is utilizing electrical current. Being hard wired has nothing to do with something being an outlet. There is a big difference between the different outlets such as lighting outlet and receptacle outlet to mention two.

    Quote Originally Posted by joe in queens
    Also circuits serving fire alarm alarm circuits are exempt from AFCI requirements per 760.21 and 760.41. Problem is NFPA 72 of the National Fire Alarm Code doesn't define interconnected smokes as fire alarms, but "regular" alarms. Yeah, that makes lots of sense.
    Article 760 is addressing fire alarm systems. What is being in this thread in single fire alarms and are not governed by 760 therefore must comply with 210.12

    Quote Originally Posted by joe in queens
    My personal opinion, which I realize might catch heat for, is put the fire alarm circuit on a standard breaker. This your life we're talking about.
    I doesn’t matter what your or my opinion is all that matters is what is called for by the code. Just because someone thinks that their system is safer does not make it so. There is more danger from arcs without the protection. This is why arc fault is required.
    Why would think that smokes on an arc fault protected circuit would be unsafe?

    Quote Originally Posted by joe in queens
    And yes, you have to use 3 conductor cable, plus ground. Never use a ground for anything but a ground. If you're local code requires 12/3 on 15A circuits like ours does in NYC, then run 12/3.

    Joe
    Here we agree.

  14. #14

    Exclamation

    The definition of "outlet" had changed with respect to AFCI. When AFCI was first introduced into code in 1999, the phrase "receptacle outlets" was specifically used. The "receptacle" part was taken out with the next code cycle.

    And not all "outlets" are created equal... what about 240V "outlets" like for room air conditioners and baseboard heaters. They're exempt by the 125V limitation. What, 240V equipment will never arc???

    Also what if an outlet located in a bedroom or bedroom closet supplies a fire alarm panel? Now what about Article 760?

    There is also the issue of AFCI type: AVZQ, AWBZ and AWCG (which doesn't seem to exist). Worse, there have been many studies showing that AFCI breakers simply DO NOT WORK under many arc conditions. Based on everything I've read, AFCI has a long way to go before it can be a real safety solution.

    And what about heat? You put enough of AFCI and GFCI breakers in a panel and the panel gets pretty warm, if not hot. This is another growing problem, and if the next code cycle expands AFCI onto more circuits, we may end-up with buildings burning down. Ins't that what AFCI is supposed to prevent?

    The reason I am so opposed to fire alarm circuits being AFCI protected is if the darn thing trips - for whatever reason - the smokes go on battery. Once the battery goes low, they start beeping. And what do all too many folks do when the things become a nusiance: REMOVE THE BATTERIES! Now there is no smoke protection at all. That is why I believe AFCI on the smoke circuit is a bad idea... just like putting GFCI protection of a refrigerator circuit would be a bad idea.

    I agree code is code, but just because something complies with code doesn't necessarily mean its safe. Receptacles on kitchen islands are a prime example. Appliances can become dangerous if say a small child or dog pulls on the cord of a coffee maker plugged into one of those side mounted receptacles. And adult can easily get caught from a cord hanging over the side, and what if the other end of that cord is attached to an electric deep fryer full of hot oil?

    All that being said, in my own home, nearly every single breaker in my home is AFCI (or GFCI) protected, well beyond code requirement. EVERY lighting circuit is AFCI, and nearly every receptacle circuit that is not GFCI is AFCI... living room, dining room, hallways, finished basement, attic, and so forth. My smoke, security, and emergency lighting circuit, however, is not AFCI.

    Joe

  15. #15

    Exclamation

    The definition of "outlet" had changed with respect to AFCI. When AFCI was first introduced into code in 1999, the phrase "receptacle outlets" was specifically used. The "receptacle" part was taken out with the next code cycle.

    And not all "outlets" are created equal... what about 240V "outlets" like for room air conditioners and baseboard heaters. They're exempt by the 125V limitation. What, 240V equipment will never arc???

    Also what if an outlet located in a bedroom or bedroom closet supplies a fire alarm panel? Now what about Article 760?

    There is also the issue of AFCI type: AVZQ, AWBZ and AWCG (which doesn't seem to exist). Worse, there have been many studies showing that AFCI breakers simply DO NOT WORK under many arc conditions. Based on everything I've read, AFCI has a long way to go before it can be a real safety solution.

    And what about heat? You put enough of AFCI and GFCI breakers in a panel and the panel gets pretty warm, if not hot. This is another growing problem, and if the next code cycle expands AFCI onto more circuits, we may end-up with buildings burning down. Ins't that what AFCI is supposed to prevent?

    The reason I am so opposed to fire alarm circuits being AFCI protected is if the darn thing trips - for whatever reason - the smokes go on battery. Once the battery goes low, they start beeping. And what do all too many folks do when the things become a nusiance: REMOVE THE BATTERIES! Now there is no smoke protection at all. That is why I believe AFCI on the smoke circuit is a bad idea... just like putting GFCI protection of a refrigerator circuit would be a bad idea.

    I agree code is code, but just because something complies with code doesn't necessarily mean its safe and code is all knowing. Receptacles on kitchen islands - a code requirement - are a prime example. Appliances can become dangerous if say a small child or dog pulls on the cord of a coffee maker plugged into one of those side mounted receptacles. And adult can easily get caught on a cord hanging over the side, and what if the other end of that cord is attached to an electric deep fryer full of hot oil? And not to get politcal, but more and more it seems the code writing body is becoming too influcened by manufacturers. I can't say that I blame them, but one has to wonder if the code is really about safety anymore or pushing new products.

    All that being said, in my own home, nearly every single breaker in my home is AFCI (or GFCI) protected, well beyond code requirement. EVERY lighting circuit is AFCI, and nearly every receptacle circuit that is not GFCI is AFCI... living room, dining room, hallways, finished basement, attic, and so forth. My smoke, security, and emergency lighting circuit, however, is not AFCI.

    Joe

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