Matt Donovan
Member
- Location
- United States
With LV wiring, sizing 90oC conductor is an easy two step process
(1) check ampacity for 90oC cable derated for conditions of use
(2) check terminations using the fully rated 75oC ampacity (assuming 75oC terminals on the equipment)
How do you check termination temperatures with MV cable? Does MV equipment even come with standard temperature ratings (60/75/90/105, etc) for the terminals?
The specific project in question has a 2MVA transformer which we are planning to feed with #2 aluminum MV-105 cable. The primary is 13.2kV so the full-load current is 88 amps, and we're a continuous load so design current is 88 x 1.25 = 110 amps. Table 310.60(C)(78) is my reference, listing 105oC ampacity of #2 AL as 130 amps. But how do I do a terminal check? Do I just require the transformer to have 105oC terminals?
FYI, the transformer is rated for 65oC rise, and the ambient is 35oC. Do these factors play into the cable sizing calcs re: cable termination?
(1) check ampacity for 90oC cable derated for conditions of use
(2) check terminations using the fully rated 75oC ampacity (assuming 75oC terminals on the equipment)
How do you check termination temperatures with MV cable? Does MV equipment even come with standard temperature ratings (60/75/90/105, etc) for the terminals?
The specific project in question has a 2MVA transformer which we are planning to feed with #2 aluminum MV-105 cable. The primary is 13.2kV so the full-load current is 88 amps, and we're a continuous load so design current is 88 x 1.25 = 110 amps. Table 310.60(C)(78) is my reference, listing 105oC ampacity of #2 AL as 130 amps. But how do I do a terminal check? Do I just require the transformer to have 105oC terminals?
FYI, the transformer is rated for 65oC rise, and the ambient is 35oC. Do these factors play into the cable sizing calcs re: cable termination?
