Jpflex
Electrician big leagues
- Location
- Victorville
- Occupation
- Electrician commercial and residential
I was trying to figure out the best type of conductors coming from pad mounted transformer secondary (primary 4800 volts to secondary 480 volt 3 phase)
3 Secondary conductors are to be chosen to go underground within properly sized schedule 80 pvc, these will feed to first point of disconnect or breaker panels within ball mill building.
However it gets confusing if I should call this feeder or service cables (feeder? Transformer secondary to main panel) Additionally, the NEC book does not list USE, USE-2 or SE Cable diameter or area so I can calculate 40% fill of conduit needed. I looked all over chapter 9 and tables 4,5,5a etc etc. nec says use must terminate outside of building which we were not planning.
So then I considered THHW rated at 75 deg cel. And good for wet locations (underground conduit) 700 kcmil at 460i amperes derated x 0.88 temperature correction 100 degrees ambient = 404.8 amperes with area of 1.10” inch x 3 conductors or 4 if ground included.
NOT SURE IF YOU CAN USE THHW FOR UNDERGROUN FEEDER/ SERVICE ENTRANCE? Or what would be more appropriate.
We are going to parallel conductors from transformer secondary to repeat this process to 3 breaker panel disconnects on order to divide 480 volt 1,203 amperes out since a conductor larger than 2000 kcmil is not practice.
Also confused if I go smaller conductor rated at higher temperature to derate under similar conductor rated at 75 degree ampacity.
Such as 500 kcmil USE-2 rated 90 degrees Celsius. 430 i amperes x ambient temp adJudgment 0.91 = 391.3 amperes (under 400 i amperes seen in 700 kcmil wire rated 75 degrees Celsius 460 i x 0.88 = 404 i amperes
What is best to use for feeder/service prior to 3 sets of breakers prior to branch circuits supplying loads? Thanks
3 Secondary conductors are to be chosen to go underground within properly sized schedule 80 pvc, these will feed to first point of disconnect or breaker panels within ball mill building.
However it gets confusing if I should call this feeder or service cables (feeder? Transformer secondary to main panel) Additionally, the NEC book does not list USE, USE-2 or SE Cable diameter or area so I can calculate 40% fill of conduit needed. I looked all over chapter 9 and tables 4,5,5a etc etc. nec says use must terminate outside of building which we were not planning.
So then I considered THHW rated at 75 deg cel. And good for wet locations (underground conduit) 700 kcmil at 460i amperes derated x 0.88 temperature correction 100 degrees ambient = 404.8 amperes with area of 1.10” inch x 3 conductors or 4 if ground included.
NOT SURE IF YOU CAN USE THHW FOR UNDERGROUN FEEDER/ SERVICE ENTRANCE? Or what would be more appropriate.
We are going to parallel conductors from transformer secondary to repeat this process to 3 breaker panel disconnects on order to divide 480 volt 1,203 amperes out since a conductor larger than 2000 kcmil is not practice.
Also confused if I go smaller conductor rated at higher temperature to derate under similar conductor rated at 75 degree ampacity.
Such as 500 kcmil USE-2 rated 90 degrees Celsius. 430 i amperes x ambient temp adJudgment 0.91 = 391.3 amperes (under 400 i amperes seen in 700 kcmil wire rated 75 degrees Celsius 460 i x 0.88 = 404 i amperes
What is best to use for feeder/service prior to 3 sets of breakers prior to branch circuits supplying loads? Thanks
