brandon05
Electrical
- Jan 10, 2005
- 5
Without using expensive software to determine the heating effect on each individual cable is there method to determine cable ampacity for multiple circuits in a single Duct Bank Conduit.
I have 11 motors, 3 lighting loads, and 2 receptacles that are 750 ft from the nearest 480 Vac source. It will be necessary to construct a Duct Bank to avoided a road. If possible I would like to use a 3 rows by 2 columns duct bank with 6" PVC conduits. See Detail 3 in Figure B.310.2 Annex B of the NEC.
Table B.310.6 in the NEC (Annex B) only allows on circuit per conduit however Table B.310.1 references Table B.310.6 in the FPN under A1. Table B.310.11 is only for Raceway or Cables with Load Diversity equal to 50 percent. Does this mean that my cable will need to be double the ampacity? Or can I apply the 100 load diversity Table 310.15(B)(2)(a)?
This does not quite make sense with the Handbook's description of how the heating effects is greatest in the middle of the duct bank. If you can apply the Adjustment Factor equally to all the conduit in the Duct Bank than it would seem that the heating effect from conduit to conduit is already considered in Table B.310.6.
Thank you for reading this long post. Any advise is appreciated. If anyone out there does have access to this expensive software and wouldn't mind doing a test run I'd appreciate. Just a thought.
Brandon Whelan
I have 11 motors, 3 lighting loads, and 2 receptacles that are 750 ft from the nearest 480 Vac source. It will be necessary to construct a Duct Bank to avoided a road. If possible I would like to use a 3 rows by 2 columns duct bank with 6" PVC conduits. See Detail 3 in Figure B.310.2 Annex B of the NEC.
Table B.310.6 in the NEC (Annex B) only allows on circuit per conduit however Table B.310.1 references Table B.310.6 in the FPN under A1. Table B.310.11 is only for Raceway or Cables with Load Diversity equal to 50 percent. Does this mean that my cable will need to be double the ampacity? Or can I apply the 100 load diversity Table 310.15(B)(2)(a)?
This does not quite make sense with the Handbook's description of how the heating effects is greatest in the middle of the duct bank. If you can apply the Adjustment Factor equally to all the conduit in the Duct Bank than it would seem that the heating effect from conduit to conduit is already considered in Table B.310.6.
Thank you for reading this long post. Any advise is appreciated. If anyone out there does have access to this expensive software and wouldn't mind doing a test run I'd appreciate. Just a thought.
Brandon Whelan