Plenum rated mike cables or not?

Discussion in 'Live Sound [BG]' started by Axtman, Feb 24, 2014.


  1. Axtman

    Axtman Supporting Member

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    Here is the situation. At my church we want to run mike cables below the floor in order to eliminate the current tripping hazard of the cables running across an isle. The floor is concrete on metal deck and the holes are already drilled. The cables would drop down through the floor, rest on top of the suspended acoustical ceiling, and pop up through the floor again.

    Do we need plenum rated microphone cables or can we just string the regular mike cables that we have now?

    We are also considering running a snake instead of individual cables. The snake might add some additional flexibility without having to get into the ceiling of the basement classrooms below. Does the snake have to be plenum rated if we go that route?

    Thanks!
     
  2. abarson

    abarson

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    As a general rule of thumb, if the wiring is going to stay in one place (i.e. installed) and especially if it crosses room barriers, it should be plenum rated.
    A competent electrician should be able to answer the question, or the local fire marshall, who is the "authority having juristriction" on such matters.

    Here's a bit more information: http://www.westpenn-wpw.com/pdfs/broadcastaudio.pdf
     
  3. bassgod0dmw

    bassgod0dmw Supporting Member

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    Plenum snake would be the way to go. Skip the individual cables.
     
  4. john m

    john m Supporting Member

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    I agree with the snake. The Plenum rating is for line voltage and fire or smoke alarm. You may not need them for a low-voltage application. Check with your local electrical inspector.
     
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  6. cashpoor51

    cashpoor51

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    Plenum rating is for all cables in a plenum voltage has nothing to do with it
    Snake is good idea but you can buy a roll of plenum rated cable and make up the ends yourself if you can solder which makes it easier to customize the lengths and where you wanna place the cables or jacks
     
  7. 1958Bassman

    1958Bassman

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    Plenum rating is for ANY cabling that is exposed, in a plenum space. If it's not in a plenum, it's not worth the added expense.
     
  8. 1958Bassman

    1958Bassman

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    If the cabling is near a cold air return, use plenum-rated cabling. If the cold air [/I]ducting[/I] is above the tiles but there's no open ducting there (the diffusers and inlets are all in the finished spaces), you shouldn't need this kind of jacket.

    Technically, cabling that's above a ceiling is supposed to be attached to the floor above, not laying there and adding weight to the ceiling, across lights, conduit and plumbing.

    How long will this cabling be? If you make your own and solder the ends on, it may be easier to install conduit from one end to the other. Mount a junction box at each end and make sure it's not open to the space above the tiles and you can avoid using plenum-rated cable. You can use a short stub for where the conduit/cable comes up through the floor and seal around it, or you could surface-mount a box on the floor at each end.
     
  9. P Town

    P Town Guest

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    Someone beat me to the conduit suggestion, but I will add, that you might want to go large enough in case you need to pull another cable in the future. (Of course, low voltage only). And, when you pull your snake, pull a spare nylon pulling line, so its there if you need to install something else.
     
  10. john m

    john m Supporting Member

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    Also, as stated, the drop ceiling can not support the snake.

    Conduit could work if you like to solder. I'd ask the local inspector if a properly supported portable snake above the drop ceiling would be acceptable---quick, clean, and cost effective.
     
  11. P Town

    P Town Guest

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    I think under certain conditions the space above a drop ceiling is considered as a plenum. Building/electrical inspectors for the jurisdiction of the occupancy have the final say. You should just ask them. My approach has been to say: I want to make sure I do this in a way that will be acceptable. Here are the circumstances, and here is what I plan to do. Please let me know if what I plan to do will pass inspection. The inspector usually will be very helpful, and will warn you if you are about to violate the interpretation of the code as adopted by the jurisdiction.
     
  12. Keithwah

    Keithwah Supporting Member

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    A Plenum space is one where they use the "plenum" of a cold air return as the ceiling cavity itself. Some larger cities, mostly east coast or Chicago, require all new cable be rated for a plenum space as more of a fire precaution. This is pretty stupid in general.

    So do you need to? Where do you live a city? small town under 100,00? If you just put it in and have real mic jack plates so it looks professionally done, then most inspectors will never look at it. So in that case, you could run standard mic/line install cable like a West Penn 291. This is used all the time in large major installations as well as tiny country Churches. If running overhead mics, which again are pointless when things like the Audix MB5050 exist these days, do use a braided shielded rubber jacket cable. These reject RF far better than the contractor grade cable. And by RF I am referring to picking up local radio stations due to creating a perfect antenna with overhead mic wire runs. But frankly, I'd just get the cables, the plates and start pulling wire.
     
  13. ggunn

    ggunn

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    Why would something like this be, or even need to be, inspected?
     
  14. lokikallas

    lokikallas Supporting Member

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    If the building burns down and they find that the cable helped the spread of the fire you would be at fault insurance wise. That's all.
     
  15. P Town

    P Town Guest

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    Plenum cable is designed to produce less harmful (arsenic gas laden?) fumes than other insulting materials (like PVC) in the event of a fire. The problem occurs, after a fire, and especially when someone dies, or gets sick, or injured, and the lawyers get involved. By conforming to code, you limit your liability when something goes wrong. Anything that can go wrong will, go wrong. Better to do it right, than be responsible for causing harm, even if it seem unlikely.
     
  16. 1958Bassman

    1958Bassman

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    Chicago requires that all cabling be in conduit, too. I have my theories about why they require what they do.
     
  17. 1958Bassman

    1958Bassman

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    Because the National Electrical Code has specific rules about all cabling, that, why. When cabling burns, the components of the smoke kill far more people than the fire. When cabling is laying on a suspended ceiling and everyone after the first installer follows their lead because "Well, everyone else did it that way" can cause the grid to fail and fall on the people/equipment below. When the ceiling is 2 stories up, it can be deadly. Code prohibits tying cabling onto plumbing and conduit, too.

    Personally, I don't want to give my liability insurance that much of a workout by doing shoddy installations.

    That said, local inspectors sometimes slack off when they do a walk-through. Usually, they're short-timers or they want the locality to be responsible. I did an office and IIRC, the electrical inspector may have taken 5 minutes on two different dates. Because this office is owned by someone I grew up with, I wasn't particularly happy about that. I prefer inspectors to be sticklers for the code.
     
  18. popgadget

    popgadget

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    A plenum is an air duct or any space that acts as one. If the space that you want to run the cables in does not serve as a duct then plenum rated insulation isn't normally required.

    I would agree with the suggestion to run a multi core cable rather than individual ones. Whether it's in a prefabricated snake or between two patch boxes that you fabricate and wire yourself is a matter of budget and capability.
    Actually the OP never mentioned how many cables needed to be run. If it's only a few, than single cables might be appropriate.
     
  19. Keithwah

    Keithwah Supporting Member

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    Well all low voltage wiring is subject to inspection and having a permit pulled to do so in almost every municipality. Just because it is audio or video doesn't exclude it. Your question why is a valid one though. It really doesn't need to be inspected nor does a permit need to be pulled. It is required because somebody is making money on it. Only a journeyman or master electrician depending on the area, is allowed to pull a permit. So basically before I can pull cable in some cities where a city inspection department sees the monetary value, force me to hire a master electrician for about $500, to go pull a permit to do the same thing I do in a smaller town with no realization of the value of hitting me for a permit, except now I pass that cost onto your church to absorb for no reason. Since I have been doing this type of work for over 30 years in a major league city, I would believe I can do a fine job without the need to pull a permit. At no time am I working with high voltage which I do feel should require a master electrician and a permit because that type of work could result in serious injury. And the city of Chicago requires a pay off to anything. I know I have had to keep a very large wad of cash on me to buy people off in order to do business. It's just the way it is there. And plenum everywhere in Chicago was intended to increase safety but.....about everything I've ever seen in their city inspection departments is really about payoffs and back door deals. But maybe that's just the hole in my pocket they burn.

    Again, me, I'd install the wire, make sure all cabling is run through cable rings available at all Home Depots, and that nothing is dangling. If you don't know how to solder very well, they make mic jacks with Phoenix block connectors these days so all you need to know is that shield is pin 1, black is pin 3, and red is pin 2 hot. Sloppy work draws attention, good work goes unnoticed. That is the secret to dodging inspectors. You might even just hire a local AV contractor, maybe even one that specializes in Churches and build a relationship with them. I have many that will pull their own cable but hire my firm to terminate because they didn't trust their solder skills.

    If this is happening during a building remodel or new construction, I will say you will need to do this type of work after the inspectors have signed off on the building, or you are almost guaranteed he will see what you are planning to do or do. And then he will want his piece, all under the guise that your Digital snake Cat6 needs a permit to carry audio to your mixer. In a new building project I always suggest working with a quality AV contractor with strong references in the worship market. They will handle all of that for you and they will save aggravation. After all a sound system is the most important thing in a church if you are going there for the right reason. To hear the Word. Past hearing the Word, fancy light fixtures, signage, carpeting and seating and glass covers palaces don't really mean a thing to a soul do they?
     
  20. seamonkey

    seamonkey

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    Absolutely nothing wrong with analog snakes. Balanced lines are stable and quiet. One may be you're going to have to wire on the connectors after running the wire, not a big deal.

    Still, You might want to look into digital snakes. They have come down in price and offer some features, like a couple of cat6 plenum rated wire could be a lot less in cost, easier to run and a lot less cable mess. Digital is more expandable over time, less subject to indifference, not too complicated. There's trade-offs but check them out.

    There are also remote control type pre-amps that sit on stage, while the console remotely controls them over cat6.
     
  21. cableguy

    cableguy Supporting Member

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    That is idiotic......

    Anyway, I've cabled a lot of buildings in Seattle. As stated it depends on if the ceiling space itself is being used for air return. If your air return is through ducts, the you're ok to run PVC cable. Support it every 4 ft or so to something other than the ceiling grid wires.
     

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