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Author Topic: recommendation for balanced cable to pull through conduit  (Read 6822 times)

Mark McFarlane

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recommendation for balanced cable to pull through conduit
« on: May 30, 2011, 09:13:27 am »

I'm looking to source some bulk balanced audio cable to pull through conduit from one side of a gym to the other. The total run will be about 140 feet.  I need to run 2 channels through the preferably same conduit.

1) What's a good cable for this type of install?
2) What size conduit to use?

Thanks,

Mark McFarlane
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Ivan Beaver

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Re: recommendation for balanced cable to pull through conduit
« Reply #1 on: May 30, 2011, 09:40:17 am »

I'm looking to source some bulk balanced audio cable to pull through conduit from one side of a gym to the other. The total run will be about 140 feet.  I need to run 2 channels through the preferably same conduit.

1) What's a good cable for this type of install?
2) What size conduit to use?

Thanks,

Mark McFarlane
We use West Penn 291.  It is available in colors-so we use the resistor color code to make thing much easier to identify-rather than marking.

Belden 2451 would be another choice-but I think it is only available in black.

DO NOT use rubber jacketed cable-you will hate yourself.  Use the plastic stuff with a thin jacket.  22 or 24 ga is fine.

The size of the conduit depends on how many wires and how many bends there are.  The more of either, the larger the conduit has to be.  A 50% fill is pretty easy to pull.

I would suggest pulling a couple of extra cables-just in case you need something later on-and at least pull a pull string with the bundle-just in case.
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Ivan Beaver
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Jonathan Kok

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Re: recommendation for balanced cable to pull through conduit
« Reply #2 on: May 30, 2011, 02:41:44 pm »

We use West Penn 291.  It is available in colors-so we use the resistor color code to make thing much easier to identify-rather than marking.

Belden 2451 would be another choice-but I think it is only available in black.

DO NOT use rubber jacketed cable-you will hate yourself.  Use the plastic stuff with a thin jacket.  22 or 24 ga is fine.

The size of the conduit depends on how many wires and how many bends there are.  The more of either, the larger the conduit has to be.  A 50% fill is pretty easy to pull.

I would suggest pulling a couple of extra cables-just in case you need something later on-and at least pull a pull string with the bundle-just in case.
I think perhaps you meant Belden 8451 ;)

Belden 8451 is commonly referred to on specification sheets, though many other manufacturers provide similar.  If you ask your preferred AV cable supplier for their version of Belden 8451, they'll be able to cross-reference it.
Anixter 317-023-2201 (I think? Off the top of my head...317 is their shielded w/ drain, 2201 is 22AWG single pair...)
Delco 33632
Provo 92516 (92516BK for black version)

Ultimately, any 22AWG Stranded, Single Pair, shielded with drain, PVC jacket.

Four of these in a 1/2" conduit shouldn't be a problem.  However, if this is a new install, and this is likely to be used in the future for other items, I'd suggest you start at 1.5".  I'd also pull a couple of cat5's at the same time.  Pretty universally usable for A/V/L.
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Ivan Beaver

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Re: recommendation for balanced cable to pull through conduit
« Reply #3 on: May 30, 2011, 04:15:50 pm »

I think perhaps you meant Belden 8451 ;)

Yes, you are correct-it has been a couple of decades since I used 8451.  The numbers get mixed up sometimes.

Thanks for correcting me.
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Mac Kerr

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Re: recommendation for balanced cable to pull through conduit
« Reply #4 on: May 30, 2011, 05:12:15 pm »

I'm looking to source some bulk balanced audio cable to pull through conduit from one side of a gym to the other. The total run will be about 140 feet.  I need to run 2 channels through the preferably same conduit.

1) What's a good cable for this type of install?
2) What size conduit to use?

Thanks,

Mark McFarlane

As long as you are going to the effort to put in conduit, you may as well run a few extra circuits, and you may want to think about making the cable be 110Ω balanced cable instead. It will be equivalent at audio frequencies, but will also be fine if you ever need to run digital audio down those lines. In an install you need to think years in advance. Once you have run conduit, making it 6 or 8 pairs is a small part of the overall cost.

Belden 8451 is what gets spec'd for regular audio cable, but there are equivalent products from other manufacturers. Belden has the big catalog, and designers know how to look up cables in it. They also make very good cable.

Mac
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Ivan Beaver

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Re: recommendation for balanced cable to pull through conduit
« Reply #5 on: May 30, 2011, 06:01:34 pm »

As long as you are going to the effort to put in conduit, you may as well run a few extra circuits, and you may want to think about making the cable be 110Ω balanced cable instead. It will be equivalent at audio frequencies, but will also be fine if you ever need to run digital audio down those lines. In an install you need to think years in advance. Once you have run conduit, making it 6 or 8 pairs is a small part of the overall cost.

Belden 8451 is what gets spec'd for regular audio cable, but there are equivalent products from other manufacturers. Belden has the big catalog, and designers know how to look up cables in it. They also make very good cable.

Mac
But did you know that the impedance to ground is different on the red wire than it is on the black wire?
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Mac Kerr

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Re: recommendation for balanced cable to pull through conduit
« Reply #6 on: May 30, 2011, 06:14:41 pm »

But did you know that the impedance to ground is different on the red wire than it is on the black wire?

I take it you are talking about 110Ω cable. How different is it? Since it is not a spec we usually pay that much attention to in regular audio cable, how tight is the tolerance in standard cable? With a low impedance output, how much influence does that difference have on the total circuit impedance balance?

Mac
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Ivan Beaver

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Re: recommendation for balanced cable to pull through conduit
« Reply #7 on: May 30, 2011, 06:27:57 pm »

I take it you are talking about 110Ω cable. How different is it? Since it is not a spec we usually pay that much attention to in regular audio cable, how tight is the tolerance in standard cable? With a low impedance output, how much influence does that difference have on the total circuit impedance balance?

Mac
I was refering to the 8451.

I remember years ago in class with Bill Whitlock on grounding, and he said he noticed the difference.  So he called up the factory and asked why.

The answer they gave him-made the whole class laugh.  They said it was due to the different colors of the wire.

But that was the correct answer.  The different colored wires are made on different machines and even with very tight tolerances, there were some differences-in both the wire and the thickness of the insulation.  Not that it was a whole lot-but enough for him to measure different rolls and see.

Of course the impedance between each of the "hot" conductors remained constant.
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Ivan Beaver
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Brad Weber

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Re: recommendation for balanced cable to pull through conduit
« Reply #8 on: May 31, 2011, 07:27:59 am »

Belden 8451/9451 or West Penn 291 are probably the 'standards' in the contracting world in the US and thus there are also many comparables.  As Mac noted, for live sound systems I've personally moved to using low capacitance, AES rated 110 Ohm cable.
 
In the US NEC defines allowable cable fill for conduit and it varies based on the number of cables, although anything more than three is 40% fill.   As Ivan mentioned there is some subjective 'fudge factor' based on the length of the run, etc. and I will generally try to oversize conduit to account for that and to allow some future capacity.
 
Obviously, some situations require or justify larger conduits, however for conduit terminating in standard boxes I will generally try to keep conduit sizes limited to a maximum of 1-1/4" as that is the largest conduit most standard boxes will handle without modification and thus is also what most E.C.s are set up to handle efficiently.
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Mark McFarlane

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Re: recommendation for balanced cable to pull through conduit
« Reply #9 on: May 31, 2011, 10:09:12 am »

Thanks everyone for your great support. 

I actually only need 1 channel (mono feed for a boombox/iPod through a Radial ProAV from the gym teachers office to a built-in amp on the other side of the gym) feeding 4 Bose 802c's in the gym's 4 corners.  The second pair was 'for future expansion'.  I'm not a big stereo fan in this type of setup. 

Currently the boombox is connected via a cheap unbalanced stereo cable over a 150' run.  I'm recommending changing that out with an 8 port balanced switch feeding one balanced audio cable, to give them some options for wiring in a projector, a remote mixer, iPod,...


Any recommendations for the AES cable? Seems like a reasonable way to go.

Belden lists db attenuation at different MHz for their AES cable.  They even seem to have coax variants.  I doubt the school would ever need anything above a 96K signal, if they did go digital in the future, which is what, about 4.6MHz for dual-channel AES at 24 bit?  (I'm probably showing my ignorance here).  I have no idea what an acceptable level of attenuation would be before noise or jitter (or whatever the issue is) becomes problematic.

Gee, spec'ing simple unbalanced audio cable just became much more complicated...

Belden 8451 is pretty cheap, $117 for 500 feet http://www.markertek.com/Cables/Bulk-Wire-Cable/Bulk-Audio-Cable/Belden-CDT-Inc/8451-010100.xhtml , the shipping cost to Saudi Arabia (where I live) will probably exceed the cable cost.

Is there a similar (pvc) multi-pair Belden cable, and would it make economic sense to pull a single multi-pair rather than multiple single-pairs cables?

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Mark McFarlane
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Turn down what's too loud.
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