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Author Topic: Flexible Conduit and Size  (Read 4495 times)

Aaron McQueen

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Flexible Conduit and Size
« on: June 06, 2007, 12:06:45 PM »

My church is doing much needed renovations.  The sound is fairly good and we won't be changing much, but I'm trying to resolve some of the infrastructure problems at the same time of the renovations.

We are moving the sound booth from a second floor location to the main floor.  The current conduit is running through the attic/crawl space to the stage, down a raceway to the stage.  Moving the sound booth to the main level means either extending that conduit down the back wall with cable extensions or new cable runs, or installing a new conduit path.

During they renovations, they are moving the duct work from the floor to the ceiling.  The current duct work is rusted and letting water in which makes the room a sauna when the heat is on.  The old duct work is going to be filled with concrete (probably not the entire duct, just the openings).  This duct makes a perfect straight path from the sound booth location to the stage.

Is there flexible conduit I could run down the ductwork to the stage?  I need flexible because of the angle at which I have to enter the duct and a smooth wall would be nice.

What size conduit?  I would like 16 lines of audio plus 5 returns, video cable, network cable, and room to spare.

Thanks, in advance for any suggestions.
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Hal Bissinger/COMSYSTEC

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Re: Flexible Conduit and Size
« Reply #1 on: June 06, 2007, 02:01:55 PM »

Google "inner duct". Inner duct is a flexible PVC tubing that is made for this type of application. Usually it is used to contain fiber within a regular conduit run but it should work well in this application. I'm not sure of the size availability but you could do multiple runs if necessary. Some even comes with a pre-installed drag line.

There is also a similar product we call "Smurf Tube" because of the blue color. It's made by Carlon.

-Hal

Brad Weber

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Re: Flexible Conduit and Size
« Reply #2 on: June 06, 2007, 03:26:22 PM »

Aaron,

Can you describe a little more about the existing ductwork.  It would be unusual to have metal ductwork direct buried below grade or where it would be in direct contact with the ground to where water would be getting into it.  Is the existing ductwork metal duct under a floor slab that is on grade or is there a concrete 'trench' that the duct is located within?  Or is it simply condensation in the duct that is causing the problems rather than water seeping in?

The existing conditions may affect just what you can do for conduit and cabling. If the path is below grade and/or wet, you may have to look at PVC conduit for the entire run or perhaps using cabling rated for exposure to water and moisture.

Just keep in mind that PVC or inner duct will not provide the EMI isolation of EMT or TW conduit, but being inside metal duct might help there.
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Brad Weber
muse Audio Video

Aaron McQueen

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Re: Flexible Conduit and Size
« Reply #3 on: June 06, 2007, 04:40:52 PM »

Brad Weber wrote on Wed, 06 June 2007 15:26

Aaron,

Can you describe a little more about the existing ductwork.  It would be unusual to have metal ductwork direct buried below grade or where it would be in direct contact with the ground to where water would be getting into it.  Is the existing ductwork metal duct under a floor slab that is on grade or is there a concrete 'trench' that the duct is located within?  Or is it simply condensation in the duct that is causing the problems rather than water seeping in?


Unfortunately it was done wrong in the first place.  The ductwork is in direct contact with the ground.  It's galvanized steel so over the years rust holes have developed and water from the ground seeps into the duct work.  During heavy rain you can actually remove the vent and see the water at the bottom of the duct.  Who know what kind of mold and other things are down there, hence the renovation.  Classic example of not doing something right the first time.

So my thought was that if this is going to be useless duct and provides a short path to the stage why not use.  However the point is taken that the conduit should be able to handle the effects of the environment.  Some of the interduct products that Hal suggested are direct burial.
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Hal Bissinger/COMSYSTEC

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Re: Flexible Conduit and Size
« Reply #4 on: June 07, 2007, 01:17:00 PM »

Brad makes a good point. Anytime you have a run of conduit below grade 9 times out of 10 there is going to be water getting into it. Even if it is a continuous run with no joints such as innerduct, temperature differences, airflow etc. can cause condensation. Over time this will cause pockets of water to form at low spots. Sealing the ends can help.

For below grade installations like this it is generally recommended that you use direct burial rated cable even though it is contained in conduit. I know that such cable is hard to come by for some of the types you will be using.

-Hal





Jason Lavoie

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Re: Flexible Conduit and Size
« Reply #5 on: June 07, 2007, 09:06:51 PM »

any chance you can cut a channel the whole way and put a hinged flap on top, converting it to a proper cable trough? or is it not in a good place for that?

Jason
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Phil LaDue

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Re: Flexible Conduit and Size
« Reply #6 on: June 07, 2007, 09:59:58 PM »

This might be silly, but couldn't you run the conduit through a large PVC pipe for an extra layer of protection against water?

Hal Bissinger/COMSYSTEC

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Re: Flexible Conduit and Size
« Reply #7 on: June 09, 2007, 09:16:18 PM »

I think the problem is that whatever is used has to be flexible. I suspect that at least the entry (and possibly the exit) to the duct is something like 90 degrees.

-Hal

Adam Kane

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Re: Flexible Conduit and Size
« Reply #8 on: June 12, 2007, 03:44:53 PM »

One commonly available type of flexible watertight conduit is SealTite (trade name).  Fairly flexible, but also fairly expensive.  They make two types.  One is just a rubber hose, the other is basically like flexible metal conduit covered in rubber/plastic.  The latter is more durable, but more expensive...especially for longer runs.  Also quite heavy once you get into sizes like 2" and larger.
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