Adding conductors to existig pipe.

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mdshunk

mdshunk

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Is there any standard (ANSI or NEMA, perhaps) that relates to the feasibility of adding conductors to a pipe that already contains conductors? Assume for the sake of this post that the NEC max fill will not be exceeded.
 
mdshunk said:
Is there any standard (ANSI or NEMA, perhaps) that relates to the feasibility of adding conductors to a pipe that already contains conductors? Assume for the sake of this post that the NEC max fill will not be exceeded.
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I don't know about a standard but the common problem that I see is the derating issue. Adding a few CCC's to an existing conduit can bring up all sorts of derating problems for the existing conductors.
 
infinity said:
I don't know about a standard but the common problem that I see is the derating issue. Adding a few CCC's to an existing conduit can bring up all sorts of derating problems for the existing conductors.
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I appreciate that response. I should have been more clear, perhaps. I was looking for any information that related to friction damage of the existing conductors while pulling extra conductors in. I know the the existing conductors should be pulled back, and the new and old should be pulled back in together. I havn't always observed that happening, and I thought that someone may have a white paper on that matter.
 
Conductor Derating

Conductor Derating

Conductor derating is probably not a problem if you are working with THHN in sizes 10, 12, and 14 AWG.

You can put as many as 9 current carrying conductors in a raceway/conduit with 70% of the 90 degree rating. The 90 degree rating for THHN in 14, 12, and 10 AWG per Table 310.16 is 25, 30, and 40 Amps; so 70% is 17.5, 21, and 28 Amps. Those values exceed the maximum OCPD for the 14 and 12, and you are permitted by NEC 240.6 to use a 30 Amp breaker with the #10 for the 28 Amp ampacity.
 
mdshunk said:
I appreciate that response. I should have been more clear, perhaps. I was looking for any information that related to friction damage of the existing conductors while pulling extra conductors in. I know the the existing conductors should be pulled back, and the new and old should be pulled back in together. I havn't always observed that happening, and I thought that someone may have a white paper on that matter.
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Use alot of pulling lubricant :)Has always worked well with smaller conductors for me.I doubt you`l find a study in regards to this subject.
 
It's not code, but strongly recommend Poly-water or Aqua-gel. Been my experience that these products are superior to Yellow77. Plus you stand a chance of getting the conductors out if you have to change(not like this has ever happened before).

If it's MV cable, make sure the pulling compound is rated for more than 600V.
 
This will not answer your question directly, and indeed it amounts to a question of my own. But the information may by of some use. I was taught (again, those words have no meaning in themselves) that if I issued a design that required additional conductors to be installed in conduits that already had conductors, then I was to insert an instruction into the project specs (or into a drawing's notes) requiring that the existing conductors be pulled out, and the new and old are to be pulled in together. I have never had occassion to use this instruction.

Does anyone with to comment on whether it is a good idea or a bad idea? Is the risk to the old conductors greater, by pulling them out and back in, or is the risk greater by having new conductors pulled while the old ones are still installed?
 
I will offer an opinion based on my experience.

In general if I pull conductors out the same ones are not going back in.

As far as pulling 12 & 10 AWGs into an existing conduit containing conductors we do that quite often.

Most times I select an existing conductor to use as a pull wire to pull the new ones in.

Common sense and care must be taken, also some wire lube on the new ones will help allot.

Pull slow and gentle, it works all the time.
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OK not all the time some times you will make a short and have to start over.
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charlie b said:

Does anyone with to comment on whether it is a good idea or a bad idea? Is the risk to the old conductors greater, by pulling them out and back in, or is the risk greater by having new conductors pulled while the old ones are still installed?
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The risk, in my limited experience, with pulling conductors on top of other conductors is that you'll create a rat's nest inside the pipe, especially if you don't use an existing conductor to pull the new ones.

And dittos on using plenty of slime to get the new ones in.
 
tallgirl said:
you'll create a rat's nest inside the pipe, especially if you don't use an existing conductor to pull the new ones.
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Big time.

If you force a snake through it gets intertwined with the existing conductors.

Using an existing conductor as a pull usually works better....unless some pinhead left tape on the conductors as they where originally pulled in.
 
Regarding pulling in extra conductors, many times conductors are pulled in as multiple pulls, even in new conduits. As suggested using some pulling lube should prevent any damage. But the question in the OP is a good one. Judging from some of the conduit runs that I've seen with the conduit literally jammed with wire I would guess that it's pretty hard to damage the insulation.
 
I have seen this happen on a pretty regular basis and never seen anyone remove the existing conductors.

Usually what I have seen done is to use an existing conductor to pull some new ones in. Plenty of lube. It seems to work fine as long as the conductor chosen as the pull wire is not tangled up inside.

I have never actually seen anyone try to put a snake into a conduit that already has wire in it.

But mostly I work with smaller gauge wires, mostly control circuits, and relative short lengths of conduit.
 
petersonra said:
I have never actually seen anyone try to put a snake into a conduit that already has wire in it.
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Pick me, pick me!

Yeah, I learned that doing so is a bad idea ...
 
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