Connection to Parallel Feeders

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bphgravity

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Assume as 300A service with parallel 1/0 feeders installed in a metal wireway after the main disconnecting means.

From the wireway, 2 - 150A panelboards will be supplied via taps from the feeders.

For ease of discussion, I will only refer to one phase conductor. From each 150A panel will be one conductor for "A" phase. In the wireway are 2 parallel "A" phase conductors.

Do the two feeder tap "A" phase conductors have to terminate to both "A" phase feeder conductors, or can they each terminate to only one or the other, or can they terminate to one each?

I can put together a wiring diagram if necessary. Thanks for any comments.
 
If your service OCPD is 300 amps, then the only way the 1/0's are in parallel is if the taps are made to both 1/0's. If you only tap 1, then you have a 1/0 conductor on a 300 amp switch and the tap rule will apply all the way back to the 300 amp switch.

That's my two cents.

Jim T
 
Bryan,
How long are the 1/0s? Do the 150 amp panels have main breakers? Are the two 150 amp panels the only loads served by the parallel 1/0s?
Don
 
What you describe sounds exactly like the arrangement of a 400A service consisting of two 200A panels. The meter fitting is equipped with two lugs per phase, and one conductor per phase goes to each panel.

If the 1/0 conductors have no other purpose but to serve the two 150 amp panels, there would be no reason to splice in the wireway. One set of the 1/0s could feed each panel. In that case, the conductors are not technically in parallel.

They are, however, tap conductors and would have to comply with those rules.

Thats what I think
Brian Dolan
 
I agree with Finhead. If you can stay within the parameters of the tap rules each panel can be supplied by one set.
 
I think Bryan better clear up the length of conductors. The OP said the 1/0's are in a wireway, which is often longer than 30', otherwise it would be a gutter. That length rules out most tap rule applications.

Jim T
 
If they install a 300A MBR they could parallel feeders across then split them and run tap conductors up to 25' to each 150A MBR panel.

The real question here is why can you run the 300A parallel feeders an unlimited distance but can only run the individual tap conductors of the same size 25'? :confused:
 
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If the 1/0 feeders from the 300 amp breaker are truely in parallel, then the tap conductors have to tap into each set of 1/0 wires.

So how are the two sets of 1/0 connected together at the other end? (The end away from the 300A breaker?) I can only assume they are split bolt connected together? Because, if they aren't connected, they aren't in parallel. And like others have said, that makes the 1/0's another tap.

If these are the only two taps, and they are very close to the where the 1/0 wires are tied together (i.e. where I think there is probably a split bolt) I guess one might be able to claim that the taps are "electrically" connected to both sets of 1/0.
 
I was hoping to not make this complicated, but that never really works out; especially on this FORUM...

This question stems from a set of plans submitted for a large office building. The plans indicate a 1200A, 3? service. The feeders from the main disco consist of 4 sets each of 4-350kcmil conductors. The feeders are installed in a 10 x 10 x 10 wireway and will serve 13 - 100A unit panelboards and 1 - 150A housepanel via taps. I am having a hard time conceptualizing how 14 tap conductors per phase are going to terminate to 4 feeder conductors per phase in the wireway...


I also don't understand why they are using this arrangement in lieu of manufactured meter pack gear. Nevermind the dertaing issue involved with the above description.
 
Bryan, we use these for this type of installation.

You can get just about any configuration (number) of Primary parallel conductor openings to Secondary tap conductor openings.


PDBfig2.gif


Roger
 
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