NEC 392 cables in tray - Help!

[KarlS]

I ran 500MCM cables - 2 per phase triplexed per NEC 392 with min 2.15 x OD. This section states to use 310.20 for tray cable. The cables are between copper bus connections on switchgear power breakers at 800at and MLO connections on 480V motor control centers. per table 310.20, I can use the 90C column due to copper bar connections on both SWGR and MCC. Based on this, my designer over sized the cables at 500MCM. I could go with 2-300MCM per phase at 90C. Here is the trouble. I have a customer that states due to NEC 110.14 C 1 - I must use 310.16 to size these cables.

I have had customers point out this section before for cable connections to breakers. Stating I must use 310.16 and the 60C column to size my cables. Molded case breakers are marked for use with 75C.

My lugs are rated 90C.

I think NEC 392 is correct. We have used this for years to size tray cable.

 

[weressl]

I ran 500MCM cables - 2 per phase triplexed per NEC 392 with min 2.15 x OD. This section states to use 310.20 for tray cable. The cables are between copper bus connections on switchgear power breakers at 800at and MLO connections on 480V motor control centers. per table 310.20, I can use the 90C column due to copper bar connections on both SWGR and MCC. Based on this, my designer over sized the cables at 500MCM. I could go with 2-300MCM per phase at 90C. Here is the trouble. I have a customer that states due to NEC 110.14 C 1 - I must use 310.16 to size these cables.

I have had customers point out this section before for cable connections to breakers. Stating I must use 310.16 and the 60C column to size my cables. Molded case breakers are marked for use with 75C.

My lugs are rated 90C.

I think NEC 392 is correct. We have used this for years to size tray cable.

- quote -

110.14 Electrical Connections.​

(C) Temperature Limitations.

The temperature rating associated with the ampacity of a conductor shall be selectedand coordinated so as not to exceed the lowest temperaturerating of any connected termination, conductor, or device.Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

(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).​

.......

(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​

......

392.11 Ampacity of Cables, Rated 2000 Volts or Less, in Cable Trays.

(A) Multiconductor Cables. ​

​

The allowable ampacity of multiconductor cables, nominally rated 2000 volts or less, installed according to the requirements of 392.9 shall be as

given in Table 310.16 and Table 310.18, subject to the provisions of (1), (2), (3), and 310.15(A)(2).
(1) The derating factors of 310.15(B)(2)(a) shall apply only to multiconductor cables with more than three current-carrying conductors. Derating shall be limited to the number of current-carrying conductors in the cable and not to the number of conductors in the cable tray.​

- end quote -
Since your equipment -terminal - is labeled for 90 Centigrade 310.14(C)(1)(b)(1) or (2) is not applicable and you are required and allowed to use the corresponding column in 310.16 with only taking ambient derating into consideration if applicable.
​

​

​

​

​

​

​

​

​

​

​

​

​