Rounding

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wasasparky

Senior Member
2.907 sq.in. = 40% fill for 3" RNC
2.927 sq.in. = My cable fill calculation (4#500,1#3 cu THHN)

Technically (for two one-hundredth's of an inch) I cannot do this.
Practically (for two one-hundredth's of an inch) there is no difference.

If they were all the same size, I could do some rounding up. ('08 Table 1 - Note 7).
What say you?
 
I use a home made Excel spreadsheet, and it came out "40%" for Sch 40.
Over the years, I've decided that when it comes out above 35% I usually go with the next size. If this is a 5' run between a box and a panel, it's probably ok.
If this is a long ductbank with a 90 or two, go to 3-1/2" or 4". It won't add that much cost, and it will make the pull orders of magnitude easier, with much less chance of damaging the insulation.

db
 
Existing underground conduits w/ 200A feeders.
Ideally I would like to use 500's to get the full 400A.
Looks like I will settle for 400's and fuse at 350A.
One is 150' under a building, other is mostly outside 250' going to generator.
If the contractor has problems pulling in 500's they (we...me) are screwed.

I suppose, we could try pulling a "ball" through to check for obstructions, roundness(or out of roundness) of conduit, etc - then decide to use 500's or 400's.

Anybody run into this?
 
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