# Thread: NEC Table 310.16 Doubt...

1. Junior Member
Join Date
Sep 2008
Location
Houston
Posts
26
Originally Posted by winnie
The NEC ampacity tables are simplifications/approximations that give the same value to a 3 conductor cable and 3 single conductors in a conduit. They also treat different types of conduit (steel, aluminum, PVC) and different sizes of conduit as being equivalent, even though they clearly cannot be.

This doesn't mean that the actual physics limit ampacity is the same; just that the two situations are treated as equivalent for NEC calculations. The NEC tables are _very_ conservative; conductors usually run much cooler than the table would lead you to expect.

-Jon
That explains it...
Thanks Jon, and thank you all for your input.

2. Originally Posted by ibarrola
It doesn't mention being installed on a cable tray, just conduit...

There's a difference in ampacity rating between a 3/C cable and a 1/C cable of the same size. So my question is, does table 360.16 show ratings for a 3/C cable only? Or does NEC have the same ratings for installing either 3 runs of 1/c vs 1 run of 3/c?

Thanks
Triangular configurations usually apply to single conductors in a cable tray.

Originally Posted by ibarrola

Does table 310.16 (old NEC Ed) show ampacity for 3/C cables only? And would this apply also for 3 runs of 1/C cables installed in a triangular configuration?
392.80(A)(2)(d) Where single conductors are installed in a triangu-
lar or square configuration
in uncovered cable trays, with a
maintained free airspace of not less than 2.15 times one con-
ductor diameter (2.15 ? O.D.) of the largest conductor con-
tained within the configuration and adjacent conductor
configurations or cables, the ampacity of 1/0 AWG and
larger cables shall not exceed the allowable ampacities of
two or three single insulated conductors rated 0 through
2000 volts supported on a messenger in accordance with
310.15(B).

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