Minimum LV cable sizing based terminal temperature is very straight forward based on NEC 2023 article 110.14. Basically, select the cable ampacity based on the terminal temperature rating utilizing Table 310.16 (either 60C or 75C depending on the equipment terminal rating). I understand that there is a second test (conditions of use) but I am not concerned with that completely separate issue. I only want to focus on the first test. A similar approach is provided by NEC 2023 article 110.40 for MV cables. However, this section provides cable ampacities based a Tables 315.60(C)(1) through 315.60(C)(20). My question is which table do you utilized. Inside the termination box, the cable should be treated as single conductor in air in my humble opinion, but I am sure this is will not be the forum consensus. NEC 110.14 basically only let's you select the cable ampacity based on Table 310.16 and purposely excludes 310.17 (which has higher ampacities). From a logic standpoint, I guess you would select the cable ampacity based on the worst-case cable configuration.
MV vs LV cable ampacity versus equipment terminal temperature ratings
- Thread starter cmmadrazo
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- Connecticut
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- Engineer
I would think 315.60(2) would dictate which table would be used.
I don't think 100.14 excludes using the ampacity table 310.17 310.15(A) says ampacity for conductors shall be as specified in the Ampacity Table 310.16 THROUGH 310.21. That includes 310.17.
I agree with your statement but this applies to the second cable ampacity test (conditions of use). My question is geared towards the first cable ampacity test which is cable size based on equipment terminal temperature limitations dictated by 110.40 (which is similar to 110.14C for LV cable sizing) and which MV cable table applies.
- Location
- Connecticut
- Occupation
- Engineer
You're trying to apply a concept from 110.14C to 110.40. They don't say the same thing.