Conduit Sizing

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i was thinking that you did the pie times r times r to get the circumference and that was your cross sectional area but wasn't sure. in the six years i've been doing this i've probably been pulling multiconductor through conduit since i started. the nec doesn't say you can't pull them through conduit it just states to size it as a single conductor pretty much and that is why i'm just double checking that i'm doing it right.

p.s. i don't really like cable pulling but for now that's what my company needs me to do so that's what i'm doing..
 
cables are no different then conductors

cables are no different then conductors

Well i pull cables in conduit we do plant work and most of the conductors for power or controls are cable , we take 40% fill just like you do when figuring regular conductors and use the formulas diameter / square inches as stated above and use tables to size the conduit , keep in mind different jackets need more space do to what type it maybe do to drag and type of outer coating some do not pull very good some do . comments ?
 
ohmhead said:
keep in mind different jackets need more space do to what type it maybe do to drag and type of outer coating some do not pull very good some do . comments ?
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Great point, code minimum and what can actually get done are two different things. :smile:
 
So the NEC allows us to pull NM cables and things like this in conduit?

For some reason I had it in my head that you weren't allowed to because of the bundling or heat dissipation of the conductors being in a jacket and then in a conduit. Someone told me that somewhere in my past.
 
steelersman said:
So the NEC allows us to pull NM cables and things like this in conduit?
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Yes, pick any raceway article and look at section 3XX.22 and it tells us we can.

IMO the NEC has always, (OK as long as I have been doing this :smile:) allowed cables in raceways but due to some code changes for a while it was not as clear. Now they have made it clear.

If I can run NM in an insulated wall why would anyone think that running it in conduit would be a heat problem? A metal conduit could actually work like a heat sink pulling heat from the cable and radiating that heat to the environment over it's increased surface area.
 
iwire said:
If I can run NM in an insulated wall why would anyone think that running it in conduit would be a heat problem? A metal conduit could actually work like a heat sink pulling heat from the cable and radiating that heat to the environment over it's increased surface area.
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True. That makes perfect sense, but you know there are some codes that don't seem to make too much sense so I just thought that this could be one of them.

I hate knowing that there are ideas or rules that I have stuck in my head that someone put there and not the NEC, and that they aren't accurate.

How about the one I have in my head that says that you are not allowed to pull a bare ground in a conduit. It has to be insulated.
 
The NEC mentions several times in 300 and chapter 9 "conductors and cables in a raceway". Chapter 9 note 9 says "shall be treated as a single conductor for calculating...". Single conductors in a raceway shall not exceed 53% of fill (or 24 inches or less at 60%).
 
cables power & control

cables power & control

Well sorry i did not mean romex, i have only been working in commercial or industrial or power plant electrical work . Now in a power plant we always pull cables meaning power or control never or rarely do we pull single conductors so i was just giving input on that .And yes romex would be a mess in conduit. cable companys like Beldon or Anxier show formulas to figure cables sizes in square inches in the back of there catalogs . Just a thought for anyone interested .be safe
 
don_resqcapt19 said:
That would be notes 5 and 9 to Chapter9, Table 1.
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OK, OK, OK. That's the last time I have the Reader's Digest Condensed Books editorial staff spot-check my posts.
ththshootingcomputer.gif
 
If you have to pull cables in pipe, here is a something to help you out. If the pipe is where it won't matter (pretty), make segmented bends. Bigger radius is better! It will save a lot of grief. Oh, and may Poly-Water be your best friend.
 
IMO the bending radius does not change the pulling force required assuming the radius was not below minimum to start with.

The only thing a larger radius sweep does is lower the sidewall pressure on the cable.
 
iwire said:
IMO the bending radius does not change the pulling force required assuming the radius was not below minimum to start with.

The only thing a larger radius sweep does is lower the sidewall pressure on the cable.
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Wouldn't that pressure translate into friction? And more force needed to overcome that friction?

Seems it's always harder to pull through 200' of pipe when theres's 2 or 3 90s in it as opposed to the exact same length but a straight shot.
 
Try pulling four coax cables in a 3/4" EMT through a standard 90, now "open one up" on a corner, and see if you personally think its different. Just like offsets, less number of degrees used, normally faster, and more betteh bro:)
 
480sparky said:
Wouldn't that pressure translate into friction? And more force needed to overcome that friction?
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With a small radius you have higher sidewall pressure but a shorter distance.

With a large radius you have lower pressure but a longer length in contact.

It's a wash.

Seems it's always harder to pull through 200' of pipe when theres's 2 or 3 90s in it as opposed to the exact same length but a straight shot.
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Of course each 90 adds tension, but a one normal size 90 will add the same tension of one large radius.
 
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