Conduit fill %

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Rich Elec.

Senior Member
Location
Pennsylvania
I s there a rule of thumb that anyone uses in conduit fill percentage of larger wire sizes, 4/0 and larger possibly?
I am wondering if 40% is too tight for larger wire with maybe 4 90's.
I know that it will physically fit, and of course a larger size will make an easier pull.
But is a smaller percentage used on a consistent basis?

Thanks,
Rich.
 
Honestly I have been part of many pulls containing 4 90's.
Machine pull.:smile:
This percentage fill is just something that I was thinking about.
Not a current situation.
 
You need to do a pulling tension and sidewall pressure (crushing force when the conductor is pulled around a bend) calculation when pulling a run with a lot of bends. The sidewall pressure is often the limiting factor.
As far as the percentage fill or the bend radius of the bends, they do not really enter into the pulling tension calculation. However the bend radius makes a huge difference in the sidewall pressure.
 
My rule of thumb is if to go up to the next trade size if:
1) the appropriate table indicates that my conduit is full. I still don't believe that the guys that came up with those tables ever pulled any wire.
2) the run is very long or than 225 degree's.
3) the wire that I'm pulling requires 3-1/2" trade size. I don's know why this trade size even exists. There's practically no price difference from 4" and it's not really any easier to handle. OK, maybe you save a little room.

These are rules of thumb and not set in stone. I break them at my leisure.... ;)
 
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