A couple of question concerning 21kv feeder circuits.
310.60 covers ampacity of conductors Rated 2001 to 35,000 Volts. Figure310.60 illustrates various duct bank arrangements for use with the Tables 310.77 through 310.86. Detail 1 illustrates 1 duct bank and detail 2 illustrates 3 duct banks. What if we are installing 2 duct banks? Per table 310.78, 350 MCM for a 21kv circuit using the 90C column, is rated for 305amps for one circuit (detail 1) and only rated for 245 amps for three circuits (detail 2). We are proposing to install 2 duct banks. What ampacity ampacity chart should be used and where does it state so.
Insulation rating of the equipment ground?
310.6 cover the need for shielding of conductors operated above 2000V, but what about the equipment ground? All 21kv MV cable has shielding. I don't remember grounds being shielded. What rating of insulation does the equipment ground need to be rated for?
X. Grounding of Systems and Circuits of 1 kV and Over (High Voltage) 250.184 Solidly Grounded Neutral Systems.
(A) Neutral Conductor. The minimum insulation level for neutral conductors of solidly grounded systems shall be 600 volts.
This tells me I can use 600V rated conductors for the neutral and I would assume my equipment ground would be the same, but I just can't find where it states that.
I would appreciate any help and guidance.
310.60 covers ampacity of conductors Rated 2001 to 35,000 Volts. Figure310.60 illustrates various duct bank arrangements for use with the Tables 310.77 through 310.86. Detail 1 illustrates 1 duct bank and detail 2 illustrates 3 duct banks. What if we are installing 2 duct banks? Per table 310.78, 350 MCM for a 21kv circuit using the 90C column, is rated for 305amps for one circuit (detail 1) and only rated for 245 amps for three circuits (detail 2). We are proposing to install 2 duct banks. What ampacity ampacity chart should be used and where does it state so.
Insulation rating of the equipment ground?
310.6 cover the need for shielding of conductors operated above 2000V, but what about the equipment ground? All 21kv MV cable has shielding. I don't remember grounds being shielded. What rating of insulation does the equipment ground need to be rated for?
X. Grounding of Systems and Circuits of 1 kV and Over (High Voltage) 250.184 Solidly Grounded Neutral Systems.
(A) Neutral Conductor. The minimum insulation level for neutral conductors of solidly grounded systems shall be 600 volts.
This tells me I can use 600V rated conductors for the neutral and I would assume my equipment ground would be the same, but I just can't find where it states that.
I would appreciate any help and guidance.