PARALLEL CONDUCTORS

[norteastel]

I am currently switching an existing 400 amp. 277/480 volt circuit from the existing MDP to a second MDP to reduce stress on the existing gear.

The existing circuit consists of 4-750kcmil's in 4" conduit.

We ran 4" conduit from the second MDP to an existing splice box in order to catch the riser circuit.

I want to run parallel 3/0(cu) or either 4/0(al) or 250kcmil(al) per phase. There is just too little room to set up the puller and reels of 500cu or 750al.

We installed 10x10 wireway were possible to eliminate pulling thru pipe. We also installed pull boxes to interrupt the length of the run and for possible splicing.

Please advise!

 

[don_resqcapt19]

Re: PARALLEL CONDUCTORS

If the grounded conductor is not a "current carrying" conductor, the parallel 3/0 copper or 250 kcmil aluminum will be ok. If there is a majority of nonlinear loads, then the grounded conductor is a current carrying conductor and you will need 4/0 copper or 300 kcmil aluminum. Note that these sizes are based only on the size of the OCPD and that 215.2(A)(1) may require larger conductors based on the Article 220 load calculations.
Don

[ May 12, 2003, 04:11 PM: Message edited by: don_resqcapt19 ]

 

[bennie]

Re: PARALLEL CONDUCTORS

Are you planning on splicing the parallel conductors?

 

[norteastel]

Re: PARALLEL CONDUCTORS

Yes I plan on splicing the parallel conductors..

 

[bennie]

Re: PARALLEL CONDUCTORS

It is not a good idea to splice parallel conductors. Maintaining equal resistance, over time, can be a factor to contribute to an eventual melt down.

There is a method, for splicing parallel conductors, that will maintain equal impedance. Each phase has to be terminated on one individual landing lug bus.

[ May 13, 2003, 01:42 AM: Message edited by: bennie ]

 

[cleveland]

Re: PARALLEL CONDUCTORS

We have numerous parallel feeders. Some have been spliced. We haven't had anymore trouble on a spliced parallel feeder than a spliced non parallel feeder. We have required the use of compression type sleeves on all splices on wire larger than #6.