NEC Conduit Fill Table vs Practical Experience

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FaradayFF

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Hi,

I noticed that when running larger cables in a conduit, pulling tension, jam ratio and other factors govern the number of conductors being installed. Even if NEC conduit fill chart allows say 6 conductors to be carried in a pipe, other calculations/factors and practical experience may limit the number of conductors to 3.

I should really prepare a calculations spreadsheet for myself that takes into account all NEC derating tables and other requirements.

Thanks all!
 
FaradayFF said:
Hi,

I noticed that when running larger cables in a conduit, pulling tension, jam ratio and other factors govern the number of conductors being installed. Even if NEC conduit fill chart allows say 6 conductors to be carried in a pipe, other calculations/factors and practical experience may limit the number of conductors to 3.

I should really prepare a calculations spreadsheet for myself that takes into account all NEC derating tables and other requirements.

Thanks all!
Click to expand...

Loading conduits to 40% fill as allowed in the NEC is almost impossible.

In large conduit runs, I will bump up a size. The cost is not that much to the ease of pulling later.
 
Much depends on the amount of bends, length, wire and how much lube you use. There is really no way to judge except experience. NEC only places a limit at 40%, there is nothing that says that 40% is possible.

-Hal
 
hbiss said:
Much depends on the amount of bends, length, wire and how much lube you use. There is really no way to judge except experience. NEC only places a limit at 40%, there is nothing that says that 40% is possible.

-Hal
Click to expand...

After many years I came to a solution that works for me.

No 1-1/4", 2-1/2" or 3-1/2" PVC conduit. Odd stuff coming back to the shop made no sense. Just bump up to the next conduit. Most of the time, if it shows copper, I will calculate for Alum and use that. Then, try for the change order. If not, I still save in labor in the long run.

1/2" doesn't make much sense now with a green wire in every pipe.

So, calculate ease of pull against the price of the material.

Overhead in EMT, you have to be a bit more careful since this is now a big labor hog. No wonder I fought to get EVERYTHING in the ground. Anytime you can move the Labor bell curve to an earlier time and spread it out to your advantage will pay big dividends.
 
IMO the 40% is just about right when the bends are limited to 360° between the pull points.
 
Gary11734 said:
Loading conduits to 40% fill as allowed in the NEC is almost impossible.

In large conduit runs, I will bump up a size. The cost is not that much to the ease of pulling later.
Click to expand...

I wouldn't say impossible, but it does seem to get harder the longer the run. I also bump up the conduit size on long runs.
 
We almost never push our fill to 40%.

I would say on an average our fill is probably 20-30%, but the majority of our work is underground pvc, so upsizing conduit isn't usually a big cost adder.
 
I was planning out a job today with a 330 foot EMT run. 300 feet of that has no bends except for a 90 about 10 feet from one end and an LB at the other. Normally I would upsize the pipe to make the pull easy, but in this case I didn't because I'm already spending a lot of $$$ on that EMT. My conduit fill is at 32%. I'll use lots of lube.
 
I typically fill to just short of the 40% maximum permitted fill. I don't see any issues, no matter what size conductors are being installed.

None of the pulling calculations that I have seen show a reduced pulling tension when you install a larger raceway.
 
I confess - I have frequently fudged over the 40% limitation. For me it has more to do with the raceway installation and how the pull is being fed into the raceway that makes the difference in go or no-go. There are also many installations where I wouldn't go near that 40% threshold due to the particular raceway configuration.

FYI - I finally made it to semi-retirement as of 1/2/2019 so I don't have the option of making up for past sins.
 
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