Parallel service

[osassady]

I have an existing 400 amp 3 phase service with 500 kcmil conductors. The work required an upgrade to 600 amp. I know code wants same conductor for parallel. 350 kcmil is good for 600 amp parallel. What is the best way to do? Just add 350 kcmil to the existing 500 kcmil?

 

[jumper]

You cannot add the two sizes for a sum total if that is what you mean.

 

[osassady]

The plan calls out for two set of 350 kcmil parallel for 600 amp disconnect. I guess my question is can I add 1 set of 350 kcmil parallel to existing 500 kcmil? Or I just add another 500 kcmil to match with the existing 500 kcmil to make it same conductor?

On drawing 2 sets (4) 350 kcmil, 4” PVC for 600 amp.

can u do 1 set 350 kcmil and 1 set (4) 500 kcmil, 4” PVC?

 

[infinity]

If adding to the existing the additional set would need to be 500 kcmil.

 

[osassady]

i Thought it would ok as long as the conductor not less than 350 kcmil. So no matter what conductor have to be the same on a parallel run. Is there any cases that parallel conductor can be different?

 

[roger]

can u do 1 set 350 kcmil and 1 set (4) 500 kcmil, 4” PVC?

Read article section 310.10(H)(2)

Roger

 

[augie47]

You can not parallel conductors of the same phase unless each conductor is of the same size,insulation types, etc, {see 310.10(H)}

(sorry, Roger)

 

[osassady]

Thank very very much you guys. ??

 

[texie]

Thank very very much you guys. ������������

I think you are saying you have only 1, 4" conduit? If so you may still have some options. If the load calcs will support a reduced neutral you might be able do this with 7, 500's in the 1 raceway.

 

[kwired]

310.10(H)(2) says:

(2) Conductor and Installation Characteristics.
The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, equipment grounding conductor, or equipment bonding jumper shall comply with all of the following:


(1) Be the same length.


(2) Consist of the same conductor material.


(3) Be the same size in circular mil area.


(4) Have the same insulation type.


(5) Be terminated in the same manner.

A major reason for most items in there is to ensure all conductors of the parallel set have the same resistance. If they are all the same resistance current should divide evenly across all the parallel paths. If you parallel one 500 with one 350 the 500 will have less resistance and will carry more current - no promises it will never carry more then it's rated ampacity either.

 

[roger]

You can not parallel conductors of the same phase unless each conductor is of the same size,insulation types, etc, {see 310.10(H)}

(sorry, Roger)

No problem Gus, you and I were posting at the same time, not like posting later just to echo something someone else or others posted.

Roger