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Thread: Fire Alarm system

  1. #1
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    Feb 2010
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    Fire Alarm system

    I'm a 4th year apprentice and am currently working on the fire alarm system for the job. I've been on this for about 2 weeks now. It's a class A system. It's my first time working anything that I can't branch or tap off wherever I want (except for t tapping the smokes). Basically, I've never done any loop wiring. It's just me working on this. The foreman is really my "jdub" right now. He's done a lot of fire alarm systems in the past so he knows the stuff inside and out. The system is an open air wiring spec, so I've almost got all the cables pulled and dropped off where they need to be. I should finish this Monday.

    I'm sure I'll learn tons more about fire alarm systems the deeper I get on this project, but I have a question. The job is radiology expansion wing on a hospital and we're interrupting the existing system. Now, when I'm tying in the horns, does it need to loop out of that interruption point, loop through all the new horns and loop all the way back in at the interruption point? Like I said, It's my first time working on loop wiring. I was going over this with the foreman yesterday and I could sense he was getting slightly irritated because I didn't completely understand. I'll get it, I'm just doing my own research right now.

  2. #2
    Join Date
    Jan 2009
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    Quote Originally Posted by Thepeelsessions View Post
    I'm a 4th year apprentice and am currently working on the fire alarm system for the job. I've been on this for about 2 weeks now. It's a class A system. It's my first time working anything that I can't branch or tap off wherever I want (except for t tapping the smokes). Basically, I've never done any loop wiring. It's just me working on this. The foreman is really my "jdub" right now. He's done a lot of fire alarm systems in the past so he knows the stuff inside and out. The system is an open air wiring spec, so I've almost got all the cables pulled and dropped off where they need to be. I should finish this Monday.

    I'm sure I'll learn tons more about fire alarm systems the deeper I get on this project, but I have a question. The job is radiology expansion wing on a hospital and we're interrupting the existing system. Now, when I'm tying in the horns, does it need to loop out of that interruption point, loop through all the new horns and loop all the way back in at the interruption point? Like I said, It's my first time working on loop wiring. I was going over this with the foreman yesterday and I could sense he was getting slightly irritated because I didn't completely understand. I'll get it, I'm just doing my own research right now.

    What do the drawings show??? You can't just come off a nac from anywhere and add on, without a plan. It's a hospital, so I'm sure a riser diagram and circuit load calcs to adjust the battery calcs were performed.

    If the circuit is a class A you must maintain an uninterrupted path from the panel back to the panel, without causing any t tapping, so yea I guess what you said, from the interruption point back to the interruption point. This would to essentially extend a circuit in the middle of an existing circuit.

    You said you know you can't t tap execept for smokes, if the circuit is a class a, there is NO tapping.

  3. #3
    Join Date
    Jan 2009
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    Massachusetts, New Hampshire border
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    I'm obviously getting old, what does 'jdub' mean? I've heard of a dubba, i.e. dummy.

  4. #4
    Join Date
    Jul 2005
    Location
    northern new jersey
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    Did any one do a load cal for the added horn/strobes added to this NAC circuit?

    I'm old too what is a"jdub"

  5. #5
    Join Date
    Jul 2006
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    San Francisco bay area
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    Technically, what you are doing is not class A. You would have 2 'interruption' points for class A, and demo-ing or abandoning the old wire that formerly joined the 2 'interruption' points.
    In battle, in forest, at the precipice in the mountains,
    On the dark great sea, in the midst of javelins and arrows,
    In sleep, in confusion, in the depths of shame,
    The good deeds a man has done before defend him.
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  6. #6
    Join Date
    Feb 2010
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    Washington state
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    Jdub means journeyman wireman.

    Sorry, I should have been more detailed earlier. The wing was built as a future expansion a few years ago and it includes a mezzanine. Obviously, shell and core wiring was done then. The electrical room is located on the mezz and there is an existing NAC panel there. We are installing another NAC panel for the actual wing itself, while the Mezz fire alarm system will still be operated by the existing NAC. So in short, there is going to be two NACs, one for the mezz, and one for the wing.

    From what I've been informed, both the smokes and the horns will be tied in with the hospitals EXISTING fire alarm system. Only the strobes will be coming from the new NAC. And sorry, I was wrong before. It's a Class B system. There are 4 strobe circuits with an EOL at the end of each.

    So, to interrupt at the existing horns, I do need to go out from that horn, loop together all the new horns and come back in to the interruption horn? And what about the smokes? Since I can T tap those, do I need eventually need to go back to the interruption smoke? Like I said, this is all new to me. I really like it though. A few months back, they had me installing and hooking up all the damper relays, which was really cool because until then, I had no hands on experience with motor controls. It was an opportunity to do something new, so I asked the GF to do the fire alarm, and here I am.

    I haven't talked in detail like this with the foreman, mainly because he has 8 other guys on the crew. So, thank you guys for helping me out.

  7. #7
    Join Date
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    Quote Originally Posted by Thepeelsessions View Post
    Jdub means journeyman wireman.

    Sorry, I should have been more detailed earlier. The wing was built as a future expansion a few years ago and it includes a mezzanine. Obviously, shell and core wiring was done then. The electrical room is located on the mezz and there is an existing NAC panel there. We are installing another NAC panel for the actual wing itself, while the Mezz fire alarm system will still be operated by the existing NAC. So in short, there is going to be two NACs, one for the mezz, and one for the wing.

    From what I've been informed, both the smokes and the horns will be tied in with the hospitals EXISTING fire alarm system. Only the strobes will be coming from the new NAC. And sorry, I was wrong before. It's a Class B system. There are 4 strobe circuits with an EOL at the end of each.

    So, to interrupt at the existing horns, I do need to go out from that horn, loop together all the new horns and come back in to the interruption horn? And what about the smokes? Since I can T tap those, do I need eventually need to go back to the interruption smoke? Like I said, this is all new to me. I really like it though. A few months back, they had me installing and hooking up all the damper relays, which was really cool because until then, I had no hands on experience with motor controls. It was an opportunity to do something new, so I asked the GF to do the fire alarm, and here I am.

    I haven't talked in detail like this with the foreman, mainly because he has 8 other guys on the crew. So, thank you guys for helping me out.
    I'm going to go out on a limb an assume (hate that word!) you have an analog addressable fire alarm control panel with remote notification appliance circuit (NAC) booster panels. Some portion of the signal line circuit (SLC) - which is what the smoke detectors, heat detectors, and control and monitor modules live on - is running through/nearby the new work area. All the circuits are Class "B".

    For the smoke detectors, if the manufacturer allows T-tapping on the Class "B" SLC, you will NOT have to return to your tap point. To do this as cleanly as possible, I would suggest you not make the tap at an existing device. Somewhere very near the device you might otherwise tap out of, install a Space Age Electronics FB4 terminal junction box. It allows you to make the T-tap in a secure fashion, and indicate clearly on the provided label which conductors are the feed in and out from the original circuit and which are the tap. You could also, if you must, make as many as three (3) taps out of the box for the SLC.

    If you are putting in a dedicated NAC for the new wing, I don't understand why you need to interrupt the existing horn/strobe circuit, unless it's possibly to get the sync signal for the strobes. Usually though, the sync signal is carried on a separate pair daisy chained to all the NAC's. In any event, you WILL need to return to the horn/strobe circuit to continue the existing circuit. This is because in the case of the smokes, etc, each device has a unique network identity, and if it falls off the network the panel knows right away. Notification appliances are "dumb", and if you T-tap that circuit there will be no way to tell if one of the appliances on the tap goes away, with the exception of a ground or short, assuming that you don't also get an open on the tap at the same time.

    By the way, if this is a hospital, most new work I know of would be a voice evac system using speaker/strobes, not horn/strobes. Are you sure it's horn/strobes?

  8. #8
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    In my state no T-tapping is allowed, everything must be a continuous loop without splices. Even Class B systems have to be wired like a Class A with the EOL resistor being mounted in the fire alarm control cabinet.

  9. #9
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    Quote Originally Posted by peter d View Post
    In my state no T-tapping is allowed, everything must be a continuous loop without splices. Even Class B systems have to be wired like a Class A with the EOL resistor being mounted in the fire alarm control cabinet.
    Ouch!! That sucking sound you hear is money draining out of the customer's wallet, for no good reason!

  10. #10
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    Quote Originally Posted by gadfly56 View Post
    Ouch!! That sucking sound you hear is money draining out of the customer's wallet, for no good reason!
    Yeah, and that's just the tip of the iceberg. There are a whole lot more rules to comply with. Our local codes also require the whole system to be in EMT or other metal raceway, but MC cable is allowed too.

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