Cablebus Terminations

[ElectrifiedChimp91]

NEC 370.80 refers to the ampacity of the conductors in Cablebus and says they may be sized based on Table 310.17 (free air). However, there's also an informational note to refer to 110.14(C) which talks about temperature limitations due to terminations. Under this section, it essentially states for over 100A circuits, "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...:
(b) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(1) Conductors rated 75°C (167°F)
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors"

So, if I'm reading this right, even if the wire in my cablebus is 90 deg C rated, and the terminations (which I've confirmed with the equipment manufacturers are also rated for 90 deg C) I'm still essentially stuck at sizing my wire based on 75 deg C of Table 310.16 even tho every part of my circuit is rated for 90 deg C and NEC 370.80 states I can size it based on Table 310.17.

Or based on the language, "Unless the equipment is listed and marked otherwise" (i.e. 90 deg C conductors & lugs) ampacity can be sized based on 90 deg C. The cable would be sized based on 310.17 but the lugs would need to still be sized based on 310.16.

For example, if I have a 4,000A Aluminum cablebus and the lugs on either end of the cablebus are 90 deg C rated and have a wire range between 750 and 1000kcmil, I could technically run in the cablebus 8 sets of 750s (8 *700=5,600A, size per 310.17, 90 deg C column) and the lugs would be rated for 1000s (8*500A=4,000A, size per 310.16, 90 deg C column).

It just seems to me like if everything is rated for 90 deg C, why would code limit you to 75 deg C?

 

[don_resqcapt19]

All of the cable bus terminations I have made have been from transformer secondaries to the line side bus of switchgear, and both of those items are typically suitable for use with conductors at their 90°C ampacities.

Typically the issue is when you terminate directly to things like circuit breakers.

 

[ron]

All low voltage switchgear, switchboards and panelboards that I have worked with, have been factory tested only up to 75 deg. You will find it challenging to find a manufacturer that lists and identifies their equipment for higher.

110.14(C)(1)(b)(2) Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors