1. Junior Member
Join Date
May 2011
Posts
14

single to parallel conductors

I was having a discussion with one of my electricians the other day and we came across something i have never seen done, but cant see why it couldnt be done.

existing condition (1) 3" GRC with (3) 500mcm conductors (1) 1/0 ground conductor. we disconnected the 3" conduit from the existing roof top AHU it was going to and run it into a J-box. due to conductor length we spliced the 500mcm in the J-box and run it to a new AHU. my electrician complained about the small bending space in the AHU and said how it would have been nice to have had smaller conductors to work with.
so my question would be: is there are code problem if we would have spliced parallel 3/0 in place of the 500mcm leading from the J-box to the new AHU? I wasnt aware of a vilation to the NEC for doing this, but thought it would be a good question.

2. The only problem you might encounter is derating. For example, in your situation, you might be changing from (3) 500 kcmils in the conduit with an amapcity of 430 amps (90°) to (6) 3/0s with an adjusted ampacity of 360 amps (90°) due to there now being 6 wires in the conduit.

3. Junior Member
Join Date
May 2011
Posts
14
Derating is where the discussion turned to in my office, but if i was going to intentionally run parallel 3/0 i would use 2". this would overall be a cost savings over the use of a single run of 500mcm in a 3" pipe

4. How would you splice the two 3/0's to a single 500MCM?

5. Junior Member
Join Date
May 2011
Posts
14
the simple way would be a polaris tap that was rated for that. (Insulated mechalical lug)

6. If you use two conduits for your 3/0s there should be no problem.
The ground would have to be in each and you would need to meet the 314.28 requirements.

7. Originally Posted by tgreen
the simple way would be a polaris tap that was rated for that. (Insulated mechalical lug)
I guess that would work. When I hear splice for conductors that large I think compression barrel and and a heat shrink insulating sleeve.

8. Originally Posted by eric9822
I guess that would work. When I hear splice for conductors that large I think compression barrel and and a heat shrink insulating sleeve.
Those are great but as you can see they will not let you do odd ball things.

I had to tap a 1600 amp feeder of four 600s with a 800 amp tap of two 600s and a 400 amp tap of one 600.

I had to get seven port Polaris terminals

9. Originally Posted by iwire

I had to get seven port Polaris terminals
Love the Polaris. What did those cost? If the line is \$120 I'll take the over.

10. Another option if there is room in the J box is Power Distribution Blocks.

Roger

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