Free Air Cable Ampacity

[Pitt123]

When can the Free Air Ampacity of cables in table 310.17 used?

I have an application where I have covered cable tray located outdoors that has several power and control cables located in it. Would this covered cable tray be considered Free Air allowing table 310.17 to be used or would this outdoor cable tray still be considered a raceway thus requiring 316.16 to be used?

 

[Smart $]

When can the Free Air Ampacity of cables in table 310.17 used?

I have an application where I have covered cable tray located outdoors that has several power and control cables located in it. Would this covered cable tray be considered Free Air allowing table 310.17 to be used or would this outdoor cable tray still be considered a raceway thus requiring 316.16 to be used?

You can only use T310.17 for the ampacity of single-conductor cables and even then there are provisions which reduce the ampacity given in the table. Refer to 392.11(B). Additionally, the ampacity must still meet 110.14(C) termination temperature requirements, which always takes you back to 310.16 unless you use the workaround.

 

[charlie b]

I agree that 310.17 cannot be used for multi-conductor cables. You didn't say this, but I will add that it also cannot be used for any conductors in a tray. To me, at least, "free air" means "swinging in the wind," so that it can dissipate heat in all directions.

But I will disagree with this statement:

Additionally, the ampacity must still meet 110.14(C) termination temperature requirements, which always takes you back to 310.16 . . . .

If you have an installation for which table 310.17 applies, and if you have conductors with 90C insulation systems, and if you have 75C rated terminations, then 110.14(C) will limit you to the 75C ampacity of table 310.17, and you don't have to look at 310.16.

 

[Smart $]

I agree that 310.17 cannot be used for multi-conductor cables. You didn't say this, but I will add that it also cannot be used for any conductors in a tray. To me, at least, "free air" means "swinging in the wind," so that it can dissipate heat in all directions.

Then can you explain why 392.11(B) refers Table 310.17 (along with Table 310.19)? True the cable is not "swinging in the wind", but as I recall, cable tray is not considered raceway.

But I will disagree with this statement: If you have an installation for which table 310.17 applies, and if you have conductors with 90C insulation systems, and if you have 75C rated terminations, then 110.14(C) will limit you to the 75C ampacity of table 310.17, and you don't have to look at 310.16.

On this one, can you explain how to get around...

110.14(C)(1) Equipment Provisions. The determination of termination
provisions of equipment shall be based on
110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed
and marked otherwise, conductor ampacities used in determining
equipment termination provisions shall be based on
Table 310.16 as appropriately modified by 310.15(B)(6).