Single conductors in cable tray with maintained space one diameter different cable sizes

[jsim]

Greetings, given NEC 2023 Section 392.80(A)(2)(c) for defining the ampacity of single conductor cables rated 2000V or less in cable trays which states:

Where single conductors are installed in a single layer in uncovered cable trays, with a maintained space of not less than one cable diameter between individual conductors, the ampacity of 1/0 AWG and larger cables shall not exceed the ampacities in Table 310.17 and Table 310.19.

To which “one cable diameter” the section refers to? In case all cables contained within the cable tray have the same diameter there is no question, but if there are cables with different sizes is the interpretation showed in the following image correct?

https://imgur.com/xuVPodY

[Image taken from: 2014 Cable Tray Manual from Eaton (Page MAN-15)]

It is to be noted that the last image taken from Eaton doesn’t refer specifically to section 392.80(A)(2)(c) but instead to the spacing required in cable trays in Class II, Division 2 Hazardous (Classified) Areas in which for example NEC section 502.10(A)(1)(6) it is stated:

… When installed in ladder, ventilated trough, or ventilated channel cable trays, cables shall be installed in a single layer, with a space not less than the larger cable diameter between the two adjacent cables unless otherwise protected against dust buildup resulting in increased heat, Type TCGERHL cable shall be installed in accordance with 336.10.

Including that “larger cable diameter between the two adjacent cables” makes it clear that the interpretation is the one showed in the image that I took from Eaton but would that interpretation also apply to section 392.80(A)(2)(c)? Or maybe the “one cable diameter” in section 392.80(A)(2)(c) is the outside diameter for the biggest cable within the cable tray? Thanks in advance

 

[paullmullen]

No facts in this response, just an opinion. The intent of 392.80 is Ampacity of Cables which is mostly a matter of keeping temperature under control. When in doubt, look at what the code says in other areas to see if there is an analogous reasoning.

• Table 310.15(B)(2)(a) attends to this for ambient temperature control... not the question here.
• Table 310.15(B)(3)(a) attends to this for multiple conductors in a conduit... close to the question here.

So this is (B)(3)(a) is not quite the question you're asking, but it does reveal how the code intends to treat conductors in close proximity. In 392.80, the notion of maintaining spacing equivalent to the diameter of the cable seems arbitrary but reasonable for managing heat. As such, I think the drawing you've done meets the intent of the code. But where the code is unclear there will be 1000 opinions.

 

[kenaslan]

I would use ETAP to calculate the ampacity in your cable