×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Multiple Circuit in Single Duct Bank Conduit

Multiple Circuit in Single Duct Bank Conduit

Multiple Circuit in Single Duct Bank Conduit

(OP)
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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources