Cablebus 370 vs 110.14C

[cmmadrazo]

I need some help on cable sizing as it applies to LV cablebus.
NEC section 370.80 permits the cablebus conductors to be sized based on Table 310.15(B)(17).
Additionally, The NEC handbook (2017) under section 370.80 makes reference to the temperature limitations of the connecting equipment but does not specifically call out section 110.14C. As with all LV equipment (most likely to be terminated with cablebus) you are limited to the 75C ampacity column under table 310.15(B)(16). If the NEC left out section 110.14C on purpose, I am not sure why. It is my opinion to correctly size the cablebus conductors, you would first size the cablebus based on 110.14C (310.15(B)(16)(75C) then utilize Table 310.15(B)(17)(90C) for the conditions of use, selecting the larger of the two cable sizes. This is the same procedure for sizing any other cable application.

I have dealt with cablebus manufacturers over the years and they all stand by utilizing Table 310.15(B)(17) solely for sizing the cablebus conductors and do not take into account 110.14(C). If you take 110.14C into account, then the cable size for cablebus and cable in cable tray would be the same. The only remaining of advantages of cablebus is reduced size as compared to cable in cable tray and a more the robust construction.

 

[david luchini]

I need some help on cable sizing as it applies to LV cablebus.
NEC section 370.80 permits the cablebus conductors to be sized based on Table 310.15(B)(17).
Additionally, The NEC handbook (2017) under section 370.80 makes reference to the temperature limitations of the connecting equipment but does not specifically call out section 110.14C. As with all LV equipment (most likely to be terminated with cablebus) you are limited to the 75C ampacity column under table 310.15(B)(16). If the NEC left out section 110.14C on purpose, I am not sure why. It is my opinion to correctly size the cablebus conductors, you would first size the cablebus based on 110.14C (310.15(B)(16)(75C) then utilize Table 310.15(B)(17)(90C) for the conditions of use, selecting the larger of the two cable sizes. This is the same procedure for sizing any other cable application.

I have dealt with cablebus manufacturers over the years and they all stand by utilizing Table 310.15(B)(17) solely for sizing the cablebus conductors and do not take into account 110.14(C). If you take 110.14C into account, then the cable size for cablebus and cable in cable tray would be the same. The only remaining of advantages of cablebus is reduced size as compared to cable in cable tray and a more the robust construction.

If I used 1/0 cable bus for a 225A feeder (1/0 cable bus has an ampacity of 230A at 75degC) then I haven't exceeded the temperature rating of any of the connected terminations, conductors, or devices. I don't see a violation of 110.14(C).

 

[cmmadrazo]

If I used 1/0 cable bus for a 225A feeder (1/0 cable bus has an ampacity of 230A at 75degC) then I haven't exceeded the temperature rating of any of the connected terminations, conductors, or devices. I don't see a violation of 110.14(C).

I believe your example exceeds the termination verification as detailed below:
Termination verification-310.15(B)(16)(75C) via 110.14C limits the ampacity of 1/0 to 150A.
Conditions of use - 310.15(B)(17)(90C) via NEC 370.80 limits the ampacity of a 1/0 to 260A.

 

[david luchini]

Termination verification-310.15(B)(16)(75C) via 110.14C limits the ampacity of 1/0 to 150A.

110.14(C) doesn't say anything about limiting the ampacity of 1/0 to 150A. It says that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device.

The 75deg rating of 1/0 cable bus is 230A. If I use the 1/0 cable bus at 230A or less, then I haven't exceeded the 75deg temperature rating of any of the terminations or devices in the circuit.

 

[ron]

110.14(C) doesn't say anything about limiting the ampacity of 1/0 to 150A. It says that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device.

The 75deg rating of 1/0 cable bus is 230A. If I use the 1/0 cable bus at 230A or less, then I haven't exceeded the 75deg temperature rating of any of the terminations or devices in the circuit.

I have struggled with this as well. This Schneider Bulletin describes it well for me, but doesn't jive with David's perspective.

https://www.schneider-electric.com/...5/en_US/Wire Terminations 0110DB9901R2-02.pdf

 

[cmmadrazo]

110.14(C) doesn't say anything about limiting the ampacity of 1/0 to 150A. It says that the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device.

The 75deg rating of 1/0 cable bus is 230A. If I use the 1/0 cable bus at 230A or less, then I haven't exceeded the 75deg temperature rating of any of the terminations or devices in the circuit.

Then read 110.14(C)(1) "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 310.15(B)(16) as appropriately modified by 310.15(B)(7)".

See the link in Ron's post below as this addresses the issue in great detail.

Does 370.80 nullify the requirements of 110.14(C) even though section 370.80 makes mention of equipment terminal temperature limitations (informational notes) but does not specifically call out 110.14(C)?

 

[david luchini]

Then read 110.14(C)(1) "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 310.15(B)(16) as appropriately modified by 310.15(B)(7)".

See the link in Ron's post below as this addresses the issue in great detail.

Does 370.80 nullify the requirements of 110.14(C) even though section 370.80 makes mention of equipment terminal temperature limitations (informational notes) but does not specifically call out 110.14(C)?

I've read 110.14(C)(1). It tells you how to determine the rating of the equipment termination provision. It doesn't tell you how to determine the ampacity of the conductor.

110.14(C) is titled "Temperature Limitations". It's purpose is to ensure that the temperature ratings of conductors, terminations and devices are not exceeded.

310.15 is titled "Ampacities for Conductors Rated 0-2000 Volts". It's purpose is to tell you how to determine the ampacity of a conductor.

370.80 tells you specifically that the ampacity of cablebus shall be in accordance with Table 310.15(B)(17), which is part of Section 310.15.

Nothing in 110.14(C) is being nullified. You still have to use the conductors at their 75 deg rating to conform with the requirements of 110.14(C).

Think of an example of a 1/0 cable bus being used as a feeder from a 225A switchboard c/b to a 225A MLO distribution panelboard. What size terminations will be installed on the c/b and the panelboard's main lugs? Would you expect to find 1/0 lugs, which 110.14(C)(1) tells us are rated for 150A, on a 225A c/b or panelboard? No, the terminations on the 225A c/b and panelboard are going to be rated for at least 225A, which 110.14(C)(1) tells us would have to be 4/0 or larger.

What would be a violation of 110.14(C)(1) would be to try to splice two sections of 1/0 cable bus together on a 225A feeder using 1/0 splice blocks.