use of NEC table 9 vs table 4

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dannyrzk

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Good morning, i'm having a little bit of problem deciding how many conduits I need when comparing two different tables.

I have a total of 95 ckts, using #10AWG as per Table of chapter 9 table 5 the cross-sectional area is .0191 in^2, then (95 *3=285 wires) total area will be 285*.0191=5.4435 in^2\using Rigid PVC according to table 4 that would be .495 @40% on a 1 1/4" rigid PVC a total of 11 conduits.


if use table 9 of the Annex, for 1 1/4" Rigid PVC I can fit 23 wires, then 285/23= 13 conduits

what am I missing here? why two different answer?

Thanks
 
dannyrzk said:
Good morning, i'm having a little bit of problem deciding how many conduits I need when comparing two different tables.

I have a total of 95 ckts, using #10AWG as per Table of chapter 9 table 5 the cross-sectional area is .0191 in^2, then (95 *3=285 wires) total area will be 285*.0191=5.4435 in^2\using Rigid PVC according to table 4 that would be .495 @40% on a 1 1/4" rigid PVC a total of 11 conduits.


if use table 9 of the Annex, for 1 1/4" Rigid PVC I can fit 23 wires, then 285/23= 13 conduits

what am I missing here? why two different answer?

Thanks
Click to expand...

According to Chapter 9, Table 5, the cross sectional area of #10 THHN, THWN, THWN-2 is 0.0211 in^2, not 0.0191 in^2.
 
When I read the first post I said OH NO-- I thought there was an error in the Tables in Annex C that I had worked on for so long. I keep waiting for someone to find an error. It's funny because the original table had been there for years and years with an error in it and nobody noticed it till fairly recently. Or maybe nobody cared to do anything about it so I assumed there may be one in this one also
 
dannyrzk said:
Good morning, i'm having a little bit of problem deciding how many conduits I need when comparing two different tables.

I have a total of 95 ckts, using #10AWG as per Table of chapter 9 table 5 the cross-sectional area is .0191 in^2, then (95 *3=285 wires) total area will be 285*.0191=5.4435 in^2\using Rigid PVC according to table 4 that would be .495 @40% on a 1 1/4" rigid PVC a total of 11 conduits.


if use table 9 of the Annex, for 1 1/4" Rigid PVC I can fit 23 wires, then 285/23= 13 conduits

what am I missing here? why two different answer?

Thanks
Click to expand...

What kind of circuits? Just wondering if your calculation of 3 wires per circuit includes an equipment grounding conductor for each circuit. You only need one per conduit, sized for the largest OCPD protecting conductors in the conduit. Or you could use the conduit for an EGC if it qualifies.
 
jimdavis said:
What kind of circuits? Just wondering if your calculation of 3 wires per circuit includes an equipment grounding conductor for each circuit. You only need one per conduit, sized for the largest OCPD protecting conductors in the conduit. Or you could use the conduit for an EGC if it qualifies.
Click to expand...
I rather doubt that PVC conduit would qualify as an EGC.

Sent from my XT1585 using Tapatalk
 
Jim's question whether the 3 wire circuit includes the EGC is still valid. 95 three-wire circuits is quite a lot in most environments.
 
With that many conductors in the raceway, hopefully you have already factored in ampacity adjustments before determining you need 10 AWG conductors.
 
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