13800 & 4160 in duck bank over 3 circuits Detail 3 in code required for conductor rateings (310.61)Table 310.77 If 6-350 mcm wires in same conduit rating them dn an additional percentage 310.15(b)(2)(a)4-6 80%. thus use table 310.77 Detail 3 then an additional derateing for 6 current carrying conductors in conduit.
350mcm 90c =315x2=630x80percent=504 amps So parallel 350 in a single conduit with 4 other hv circuits in the ductbank .Rateing of conductors = 504 amps
The cables in same duct are single conductors 4160 350 mcm x 6 plus ground. Legal and designed that way not by me but by the eng. I just feel if you should derate for amount of circuits in the duct per details in code and if you put 6 current carring condutors in one pipe derateing must also apply.They are parallel conductors going to the same overcurrent device.
Re: High Voltage ductbank Derating#90904 12/17/0407:20 PM12/17/0407:20 PM
I agree with your concern. I could not find any derating info for the hi voltage cable. Suggest you contact Okonite at their site Okonite.com. Just for information what size is the cable and overcurrent device?
Re: High Voltage ductbank Derating#90905 12/20/0403:28 PM12/20/0403:28 PM
In your other post you said the transformer was rated at 1935 kva at 4.16 kv. Thats about 277 amps primary. One ckt of #350 cable is rated in duct at about 385 amps in table B310.77. Since you have 2 circuits of #350, even if you derate 50%, you should have adequate capacity for the transformer.
Re: High Voltage ductbank Derating#90907 12/22/0408:08 AM12/22/0408:08 AM
Read my ist post for conductor rateings . Detail 3 90% rateing 315 not 385 amps on the wire . Also the derateing was my interest as I know full load current of the Transformer and even with voltage drop I feel the wire is oversized for the projected use.(remember Over 3 circuits ductbank detail 3 not detail 1(310.77).
Re: High Voltage ductbank Derating#90908 12/22/0406:58 PM12/22/0406:58 PM
310.16 tables (0-2000volts) 310.15 Ampacties for conductors rated 0-2000 volts. This is 4160 -13800 volts . read ist post I put up for temp rateings and derateing.
310.4 last sentence (conductors in parrallel shall comply with the provisions310.15 (b)(2)(a) But again 310.15 Ampacities for CONDUCTORS Rated 0-2000 volts! I think derateing of HV conductors should apply to this section but only 310.77 really deals with them directly. as far as Insulation 100% or 133% read notes bottom of table 310.64 328.80 Ampacitys of MV cable Shall be determined by 310.60 ( which I referenced in orginal post)