I have a large commercial project served by 3 - 3000A service sections for 277/480 3ph lighting and HVAC equipment. The common duct bank from the service yard to the building has up to 20 - 4" conduit(incl spares)in five groups of 4's with 24" spacing in between and 18" cover. The typical conduit has 4 - 750 KCMIL and 1 - #4/0 GND. Plans call for a "river" of concrete slurry to encase the conduit w/6" of slurry all around. Heat dissipation has become an issue - but NEC '99 Article 310 does not offer any guidelines as to when heat build-up becomes a problem. Are there guidelines for the max number of conduit at "X" voltage that can be placed in a duct bank before heat becomes a problem?
I apologize for trying to be succinct with my first post. Here's the actual condition by bank.
bank 1: 1400A, 4-4"C w/4-750 KCMIL, 1-#4/0 GND.
bank 2: 2 - 3"C and 2 -4"C all spares
bank 3: 1000A, 3-4"C w/4-500 KCMIL, 1-#2/0 GND., 1-4"C spare
bank 4: 1000A, 3-4"C w/4-500 KCMIL, 1-#2/0 GND., 1-4"C spare
bank 5: 600A, 1-4"C, 1-2 1/2"C wire size unknown
Distance from SES to elec. room - 500ft. Is heat buildup and the loss of ampacity a concern? Is filling the void between banks w/concrete beneficial, or should the banks be individually formed?
[ January 16, 2004, 01:50 PM: Message edited by: erniep ]
I apologize for trying to be succinct with my first post. Here's the actual condition by bank.
bank 1: 1400A, 4-4"C w/4-750 KCMIL, 1-#4/0 GND.
bank 2: 2 - 3"C and 2 -4"C all spares
bank 3: 1000A, 3-4"C w/4-500 KCMIL, 1-#2/0 GND., 1-4"C spare
bank 4: 1000A, 3-4"C w/4-500 KCMIL, 1-#2/0 GND., 1-4"C spare
bank 5: 600A, 1-4"C, 1-2 1/2"C wire size unknown
Distance from SES to elec. room - 500ft. Is heat buildup and the loss of ampacity a concern? Is filling the void between banks w/concrete beneficial, or should the banks be individually formed?
[ January 16, 2004, 01:50 PM: Message edited by: erniep ]