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bdn2004 (Electrical) (OP)
17 Feb 07 9:22
We have a project where we will be relocating a number of 150 Hp, 480V pump motors about 50'.  The existing feeders are installed in an underground duct bank. The feeders are approximately 300' in length.

To re-feed the motors overhead will be very expensive. Adding a pullbox at the existing location or installing a manhole are also not options.

The entire area between the new and old location will be excavated prior to building a foundation for the new equipment, thus exposing the existing duct bank.

It seems a shame not to re-use the existing, but I have never heard of extending underground duct bank ..Can this be done?  Any issues?  
wareagle (Electrical)
17 Feb 07 14:08
Don't know of a reason not to extend the duct. You would have to chip the concrete back enough to get to the duct. Problem is not to damage the existing cable.
tinfoil (Electrical)
19 Feb 07 8:28
How about just building a new duct bank right beside the old one?

MAKE SURE that you document/update all of your exisitng records.
Helpful Member!  EEJaime (Electrical)
20 Feb 07 15:52
You cannot splice conductors in a conduit, so I assume you would pull out the existing conductors, intercept and extend the duct bank to the new location and re-pull all new conductors.

If this is your intent, it is possible.  You would need to specify the chipping back of the concrete enough to expose the conduit beyond where, ( it is assumed), the elbows currently bring it up vertically through the floor to the existing motors, and then extend the horizontal conduit runs to your new equipment locations.

I don't know your configuration, but I have also left the risers in place, installed an empty switchgear section to use as a pullbox above grade and extended them either back down underground, or overhead.  Not the most elegant solution, but effective and one of the least costly options as you would utilize most of the existing duct bank.

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