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Thread: NFPA 72 Class A Wiring separation

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    NFPA 72 Class A Wiring separation

    I reviewed three past threads all the way back to 2011 and they don't specifically answer this question...

    First here is the code section (and the appendix clarification):

    12.3.7* Class A and Class X circuits using physical conductors (e.g., metallic, optical fiber) shall be installed such that the outgoing and return conductors, exiting from and returning to the control unit, respectively, are routed separately. The outgoing and return (redundant) circuit conductors shall be permitted in the same cable assembly (i.e., multi-conductor cable), enclosure, or raceway only under the following conditions:

    (1) For a distance not to exceed 10 ft (3.0 m) where the outgoing and return conductors enter or exit the initiating device, notification appliance, or control unit enclosures
    (2) For single raceway drops to individual devices or appliances
    (3) For single raceway drops to multiple devices or appliances installed within a single room not
    exceeding 1000 ft2 (93 m2) in area

    A.12.3.7 A goal of 12.3.7 is to provide adequate separation between the outgoing and return cables. This separation is required to help ensure protection of the cables from physical damage. The recommended minimum separation to prevent physical damage is 12 in. (300 mm) where the cable is installed vertically and 48 in. (1.22 m) where the cable is installed horizontally.

    My focus is on parts (1) and (2) of 12.3.7 and what the distinction is between them. I think that per #2 could run a single conduit with incoming and outgoing conductors 15 feet horizontally and down the wall 14 feet (or basically any distance) as long as it is terminated in a single device with no other outgoing conductors.

    Where #1 would come in to play would be if I was running from a junction box to to first device and then extending on to another device in another room (to avoid reference to #3). So, say I have back to back strobes in two bathrooms. I would run one conduit with 4 conductors to the first device and a short stub to the second device. But even if that is true exactly where does the rule work? Is the ten feet in this application a combination of both conduit runs, or does each device get 10 feet of shared conductor?

    Another application where I think rule one would be typical is a drop that has a horn/strobe and then directly below it a pull station. I assume this is a perfect example of where the 10 feet comes in to play. I will either need to separate incoming and outgoing or run a drop per device because the job I am envisioning has 22 foot open ceilings.




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    Quote Originally Posted by Strathead View Post
    I reviewed three past threads all the way back to 2011 and they don't specifically answer this question...

    First here is the code section (and the appendix clarification):

    12.3.7* Class A and Class X circuits using physical conductors (e.g., metallic, optical fiber) shall be installed such that the outgoing and return conductors, exiting from and returning to the control unit, respectively, are routed separately. The outgoing and return (redundant) circuit conductors shall be permitted in the same cable assembly (i.e., multi-conductor cable), enclosure, or raceway only under the following conditions:

    (1) For a distance not to exceed 10 ft (3.0 m) where the outgoing and return conductors enter or exit the initiating device, notification appliance, or control unit enclosures
    (2) For single raceway drops to individual devices or appliances
    (3) For single raceway drops to multiple devices or appliances installed within a single room not
    exceeding 1000 ft2 (93 m2) in area

    A.12.3.7 A goal of 12.3.7 is to provide adequate separation between the outgoing and return cables. This separation is required to help ensure protection of the cables from physical damage. The recommended minimum separation to prevent physical damage is 12 in. (300 mm) where the cable is installed vertically and 48 in. (1.22 m) where the cable is installed horizontally.

    My focus is on parts (1) and (2) of 12.3.7 and what the distinction is between them. I think that per #2 could run a single conduit with incoming and outgoing conductors 15 feet horizontally and down the wall 14 feet (or basically any distance) as long as it is terminated in a single device with no other outgoing conductors.

    Where #1 would come in to play would be if I was running from a junction box to to first device and then extending on to another device in another room (to avoid reference to #3). So, say I have back to back strobes in two bathrooms. I would run one conduit with 4 conductors to the first device and a short stub to the second device. But even if that is true exactly where does the rule work? Is the ten feet in this application a combination of both conduit runs, or does each device get 10 feet of shared conductor?

    Another application where I think rule one would be typical is a drop that has a horn/strobe and then directly below it a pull station. I assume this is a perfect example of where the 10 feet comes in to play. I will either need to separate incoming and outgoing or run a drop per device because the job I am envisioning has 22 foot open ceilings.


    #1 includes the FACP. They don't want an unlimited run to the panel which would kind of defeat the whole purpose of Class A.

    Yes, that's the way I see it too.

    I'm not with you on that. The junction box is not a control unit enclosure. One device with co-mingled paths per drop.

    Suppose you have an FACP is a large rectangular warehouse, mounted on the wall with the top of the cabinet about 5' AFF. Say the ceiling height is 30 feet. For the sake of argument, you are required to run the NAC at a height of 20 feet AFF along the walls. You can come out of the top of the cabinet and run the feed and return legs of the circuit in the same conduit until 10 feet above the cabinet, or 15 feet AFF. Now you have to branch left and right for 6 inches each and run the feed in one conduit and the return in the other for an additional 5 feet. Now you are 20 feet AFF and you have met the separation requirements of 1 foot for the vertical portion of the installation and the requirement of 12.3.7(1). By the way, I always take the separation to be edge to edge, not center to center. Now you start running the feed clockwise around the room. When you get to the spacing along the wall that you need to put the first horn/strobe, you drop down out of a tee, or junction box if you want, to between 84" and 96" such that the entire lens of the strobe is between those two marks. For the sake of argument, say the top of the junction box the device is mounted to is 90" AFF. Your drop is going to be 12 feet 6 inches, or within the guideline of 12.3.7(2). Rinse and repeat for all the remaining drops until you get back to the panel.

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    Quote Originally Posted by gadfly56 View Post
    #1 includes the FACP. They don't want an unlimited run to the panel which would kind of defeat the whole purpose of Class A.

    I'm not with you on that. The junction box is not a control unit enclosure. One device with co-mingled paths per drop.

    But the junction box has nothing to do with my scenario. #1 includes ANY initiating device or notification appliance as well as control unit. "enter or exit the initiating device, notification appliance, or control unit" So I feel my original questions about the scenarios I presented still remains unanswered. I do appreciate your clarification however.


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    Quote Originally Posted by Strathead View Post
    But the junction box has nothing to do with my scenario. #1 includes ANY initiating device or notification appliance as well as control unit. "enter or exit the initiating device, notification appliance, or control unit" So I feel my original questions about the scenarios I presented still remains unanswered. I do appreciate your clarification however.
    I'm not sure I understand your scenario, but I haven't had my caffeine this morning. Since exception #1 only says "conductors", I take that to mean you could have exposed cable or wire and the limitation is 10 feet. If you put the conductors in raceway as in exception #2, it looks like you have unlimited length. In either case, it's to a single device, unless you are using exception #3 for a room under 1,000 square feet but you specifically excluded that. I don't understand why you think you can wire two devices, such as the back-to-back strobes in adjacent rooms using 4-conductor cable.

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    Quote Originally Posted by gadfly56 View Post
    In either case, it's to a single device, unless you are using exception #3 for a room under 1,000 square feet but you specifically excluded that. I don't understand why you think you can wire two devices, such as the back-to-back strobes in adjacent rooms using 4-conductor cable.
    #1 doesn't say it is for a single device and I firmly believe it doesn't mean a single device or it would say so. In fact the last letter is plural s as in multiple devices. As long as the length of the conductors don't exceed 10 feet that there is nothing in #1 that says it can't feed 10 devices. My question is more along the lines of whether that 10 feet is additive or cumulative.


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    Quote Originally Posted by Strathead View Post
    #1 doesn't say it is for a single device and I firmly believe it doesn't mean a single device or it would say so. In fact the last letter is plural s as in multiple devices. As long as the length of the conductors don't exceed 10 feet that there is nothing in #1 that says it can't feed 10 devices. My question is more along the lines of whether that 10 feet is additive or cumulative.
    I agree you can feed multiple devices using #1 as long as total length of cable or raceway does not exceed 10'.

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    Quote Originally Posted by Strathead View Post
    #1 doesn't say it is for a single device and I firmly believe it doesn't mean a single device or it would say so. In fact the last letter is plural s as in multiple devices. As long as the length of the conductors don't exceed 10 feet that there is nothing in #1 that says it can't feed 10 devices. My question is more along the lines of whether that 10 feet is additive or cumulative.
    Granting for the moment that more than one device is allowed, at a minimum it is cumulative, otherwise you could wire the entire loop this way completely confounding the separation requirement.

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    Quote Originally Posted by Strathead View Post
    I reviewed three past threads all the way back to 2011 and they don't specifically answer this question...

    First here is the code section (and the appendix clarification):

    12.3.7* Class A and Class X circuits using physical conductors (e.g., metallic, optical fiber) shall be installed such that the outgoing and return conductors, exiting from and returning to the control unit, respectively, are routed separately. The outgoing and return (redundant) circuit conductors shall be permitted in the same cable assembly (i.e., multi-conductor cable), enclosure, or raceway only under the following conditions:

    (1) For a distance not to exceed 10 ft (3.0 m) where the outgoing and return conductors enter or exit the initiating device, notification appliance, or control unit enclosures
    (2) For single raceway drops to individual devices or appliances
    (3) For single raceway drops to multiple devices or appliances installed within a single room not
    exceeding 1000 ft2 (93 m2) in area

    A.12.3.7 A goal of 12.3.7 is to provide adequate separation between the outgoing and return cables. This separation is required to help ensure protection of the cables from physical damage. The recommended minimum separation to prevent physical damage is 12 in. (300 mm) where the cable is installed vertically and 48 in. (1.22 m) where the cable is installed horizontally.

    My focus is on parts (1) and (2) of 12.3.7 and what the distinction is between them. I think that per #2 could run a single conduit with incoming and outgoing conductors 15 feet horizontally and down the wall 14 feet (or basically any distance) as long as it is terminated in a single device with no other outgoing conductors.

    Where #1 would come in to play would be if I was running from a junction box to to first device and then extending on to another device in another room (to avoid reference to #3). So, say I have back to back strobes in two bathrooms. I would run one conduit with 4 conductors to the first device and a short stub to the second device. But even if that is true exactly where does the rule work? Is the ten feet in this application a combination of both conduit runs, or does each device get 10 feet of shared conductor?

    Another application where I think rule one would be typical is a drop that has a horn/strobe and then directly below it a pull station. I assume this is a perfect example of where the 10 feet comes in to play. I will either need to separate incoming and outgoing or run a drop per device because the job I am envisioning has 22 foot open ceilings.


    This is for a class A scenerio.
    Class A means your signal goes out from panel to first device and to all other subsequent devices and from the last device it comes straight back to the panel. This is for integrity of the system, panel will send signal from both sides insuring system will work if the wires cut somewhere along the way way. What you are talking about is only applicable at the panel location where your outgoing signal meets the signal from the last device.

    Sent from my SM-N950U1 using Tapatalk

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    Quote Originally Posted by Ubiquitous View Post
    This is for a class A scenerio.
    Class A means your signal goes out from panel to first device and to all other subsequent devices and from the last device it comes straight back to the panel. This is for integrity of the system, panel will send signal from both sides insuring system will work if the wires cut somewhere along the way way. What you are talking about is only applicable at the panel location where your outgoing signal meets the signal from the last device.

    Sent from my SM-N950U1 using Tapatalk
    I'm pretty sure I covered that in post #2.

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