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Author Topic: Conduit Wire Pulling  (Read 2838 times)

Mike Sokol

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Conduit Wire Pulling
« on: January 13, 2014, 09:27:07 am »

I just did final setup on a sound system at a big church over the weekend, and they hired a data-com company to pull new digital snake wiring through existing conduits in the concrete floor. They tried to add multiple CAT-6 cables into the already filled conduits without pulling out the old wiring first, and stacked up the e-taped joints so badly that they got all the wiring stuck in the conduit and had to abandon that run. That was a big PITA for me since there were data runs missing where we expected them to be. After discussing the contractors with the guy in charge, our take on it was that since data-com people generally don't do conduit work they did something silly. But a good industrial electrician knows all kinds of tricks and things to avoid while pulling wires in conduit and would never have made this goof. 

It's been a while since I've done any serious conduit wiring, so I don't feel qualified to write a primer on this thread. But if any of you are conduit/wiring guys, could you take a little time to write out some of the basics of conduit wiring and what to avoid. You know, how to use Greelee punches and why you need to de-burr the conduit, what are slow-els and fill percentages and all that sort of stuff. At least knowing the basics of conduit installation and wire pulling could help someone else evaluate an installation BEFORE the concrete is poured and the wires are pulled.

Al Keltz - Whirlwind

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Re: Conduit Wire Pulling
« Reply #1 on: January 13, 2014, 11:21:22 am »

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Jonathan Johnson

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Re: Conduit Wire Pulling
« Reply #2 on: January 13, 2014, 12:10:04 pm »

I'm by no means an expert conduit installer, but here's what I can contribute:
  • NEC allows a maximum of 360 of bends (equivalent to four 90s) between pull points. That will be a hard pull; if possible, limit to 180.
  • Plastic bushings should be used at every conduit fitting that is attached with a locknut inside the box. I don't know the code requirements on bushings, but even if not required they are not prohibited, and I've scraped the insulation on wires pulling them through unbushed fittings. They are inexpensive and a good idea.
  • Always install a pull string in conduit. When adding wires using the pull string, pull a replacement string through. Probably not necessary if the conduit is at fill capacity.
  • With line voltage service, connections are not permitted in conduit bodies UNLESS the conduit body is bonded to the equipment grounding conductor (if metal) AND the connectors and conductors do not exceed the fill limits for the volume of the body.
  • When pulling conductors, use listed pulling lube. It will make the pull easier with less force, and reduce the chance of abrading the insulation.
  • Some cables (such as type NM nonmetallic sheathed cable, plenum-rated cable, or other low-voltage wire) may be run along the surface without using conduit. However, where they could be subject to abuse -- such as anywhere from the finished floor to eight feet above -- they are required to be protected. The typical method of protection is to run the cables in conduit. The conduit should terminate with a bushed fitting where the cable exits.
  • One big but often overlooked reason for a maximum fill capacity is heat dissipation. That makes me wonder about the wisdom of installing lots of wires in a large conduit -- might be better to have multiple smaller conduits in some situations.
« Last Edit: January 13, 2014, 12:13:08 pm by Jonathan Johnson »
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Rob Spence

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Re: Conduit Wire Pulling
« Reply #3 on: January 13, 2014, 01:02:17 pm »

I'm by no means an expert conduit installer, but here's what I can contribute:
  • NEC allows a maximum of 360 of bends (equivalent to four 90s) between pull points. That will be a hard pull; if possible, limit to 180.
  • Plastic bushings should be used at every conduit fitting that is attached with a locknut inside the box. I don't know the code requirements on bushings, but even if not required they are not prohibited, and I've scraped the insulation on wires pulling them through unbushed fittings. They are inexpensive and a good idea.
  • Always install a pull string in conduit. When adding wires using the pull string, pull a replacement string through. Probably not necessary if the conduit is at fill capacity.
  • With line voltage service, connections are not permitted in conduit bodies UNLESS the conduit body is bonded to the equipment grounding conductor (if metal) AND the connectors and conductors do not exceed the fill limits for the volume of the body.
  • When pulling conductors, use listed pulling lube. It will make the pull easier with less force, and reduce the chance of abrading the insulation.
  • Some cables (such as type NM nonmetallic sheathed cable, plenum-rated cable, or other low-voltage wire) may be run along the surface without using conduit. However, where they could be subject to abuse -- such as anywhere from the finished floor to eight feet above -- they are required to be protected. The typical method of protection is to run the cables in conduit. The conduit should terminate with a bushed fitting where the cable exits.
  • One big but often overlooked reason for a maximum fill capacity is heat dissipation. That makes me wonder about the wisdom of installing lots of wires in a large conduit -- might be better to have multiple smaller conduits in some situations.
Good advice.
If space allows, make 90 degree turns with a pair of 45s. It will make the pull easier.

If there are many wires already in the pipe, adding any can be a problem due to the pull string (used to pull a pull tape, not wire) being twisted among the existing wires.
If that is the case, the only way I know is to pull out the existing bundle while pulling in a new string and then pull all the wires back at one time.


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Jamin Lynch

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Re: Conduit Wire Pulling
« Reply #4 on: January 13, 2014, 01:28:38 pm »

I'm not an electrician so I can't say much as far as that goes.

Audio/video:

If new construction I work with the owner and architect from the very start. I discourage them from locating, especially the sound booth, in a location that will require conduit to be run in the slab. Put the sound booth where the cabling can be run over head...that will at least make the conduit issues go away.

If conduit must be run in the slab, I always go for much larger than they think they will ever need. 3" or 4" and more than just one run. Leave PLENTY of room for expansion. It may seem like over kill today, but it will fill up fast over the years.

PVC if code allows. No sharp edges.

As few bends as possible

Extra long sweep elbows

Lots of lube

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Lyle Williams

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Re: Conduit Wire Pulling
« Reply #5 on: January 13, 2014, 03:24:26 pm »

We've seen lots of overfilled conduit.  It seems a bit extreme to abandon a run.  Couldn't all the existing cable be pulled out and the whole thing started again?  Was there an alternate conduit path?

If we are building a list of cable pulling mistakes:

Hauling cable with laid (twisted construction) rope.  It puts twists into the cable.

Letting cable run off the end of a spool.  Again, twists in the cable.

Not watching what is going on and letting a cable kink enter the conduit.  That'll jam somewhere.

Too much tension on the pull.  Yes, the cable gets through, but will it work?


In my comms world, there is no way we could get 360 degrees of bends between pits.  90 maybe.  And they would need to be gradual.
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Jason Lavoie

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Re: Conduit Wire Pulling
« Reply #6 on: January 13, 2014, 04:29:09 pm »

I just did final setup on a sound system at a big church over the weekend, and they hired a data-com company to pull new digital snake wiring through existing conduits in the concrete floor. They tried to add multiple CAT-6 cables into the already filled conduits without pulling out the old wiring first, and stacked up the e-taped joints so badly that they got all the wiring stuck in the conduit and had to abandon that run. That was a big PITA for me since there were data runs missing where we expected them to be. After discussing the contractors with the guy in charge, our take on it was that since data-com people generally don't do conduit work they did something silly. But a good industrial electrician knows all kinds of tricks and things to avoid while pulling wires in conduit and would never have made this goof. 

It's been a while since I've done any serious conduit wiring, so I don't feel qualified to write a primer on this thread. But if any of you are conduit/wiring guys, could you take a little time to write out some of the basics of conduit wiring and what to avoid. You know, how to use Greelee punches and why you need to de-burr the conduit, what are slow-els and fill percentages and all that sort of stuff. At least knowing the basics of conduit installation and wire pulling could help someone else evaluate an installation BEFORE the concrete is poured and the wires are pulled.

Even if they managed to get the wires through you might not know until later if they damaged the existing wires. all it takes is for the pull string to get wrapped around, or to pinch them on the inside of a bend and it'll work its way through like a saw.
The only time I'd pull new wires in without taking out the existing is if the run is practically straight (no danger of the corner damage) or if the conduit is relatively empty and I can use a fiche to pull so that we don't damage the existing wires.

If there is even a slight chance that the pull will be tough you'd be amazed how much the termination and taping of the cable can make a difference. some electrical tapes have more friction than others, etc.

Jason
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Jonathan Johnson

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Re: Conduit Wire Pulling
« Reply #7 on: January 13, 2014, 05:43:04 pm »

Do not combine line voltage and low voltage/datacomm circuits in the same raceway.

Besides the high possibility of interference, it's a code violation.

The NEC defines raceway thusly:

Quote
Raceway. An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.

There are raceway assemblies that allow line voltage and low voltage/datacomm circuits to run in separate channels.
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Mike Sokol

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Re: Conduit Wire Pulling
« Reply #8 on: January 13, 2014, 05:51:38 pm »

If there is even a slight chance that the pull will be tough you'd be amazed how much the termination and taping of the cable can make a difference. some electrical tapes have more friction than others, etc.

My own wire pulling background was industrial, and we did 2" to 4" to 6" conduit all the time on VERY long runs (several hundred feet). To get the pull string though the conduit initially we used something that looked like a little rocket with a spool of thread on the back. The rocket fit perfectly inside the diameter of the chosen conduit, and you just hung the thread out of the end and tied it off. Then we had a rubber stopper that fit into the end of the conduit with a fitting for a tank of pressurized air. I think we used a tank of compressed nitrogen to shoot the little rocket through the conduit while the thread unwound off the spool. After the rocket popped out the far end of the conduit, we would tie on a light nylon rope and pull it back, then tied on a piece of aircraft cable and pulled it the other way for the wire pull of 600 amp 4-wire 3-phase. To pull that much wire we jacked up a fork truck and wrapped the cable around the wheel and ran it real slow. One guy on the far end with all four wire spools kept lubing the wire with a paintbrush and making sure it fed into the conduit without any kinks.

This was also when I learned about properly taping the wires to the pull tape or cable. One electrician I worked with would spend what seemed to be a very long time taping everything up, but he said that was time well spent. I must admit that I never remember seeing him jam a cable pull or lose a splice.

Frank Koenig

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Re: Conduit Wire Pulling
« Reply #9 on: January 13, 2014, 07:14:25 pm »

For shorter runs most of us use a metal fish tape for the initial "stringing" of the conduit. For longer runs I've used a shop vac and a thin nylon cord with great success.

The interesting thing is that you don't need to put any sort of piston on the end of the cord. Once it is started, aerodynamic drag on the
cord's surface is sufficient to pull it along. In a 1.5 or 2 in. conduit with 50 ft. of cord out, it pulls so hard that it will snatch it out of
your hand in a moment of inattention. If the cord isn't tied to the spool you can end up with a big wad of cord inside the shop vac. (How
would I know this?) Anyhow, it works great, at least for the smaller sizes of conduit.

--Frank
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