Parallel conductors feeding a three phase motor

[podobing]

Good Morning,
I have a question regarding the partial replacement of parallel conductors feeding a three phase, 200 HP, 575 volt motor.
The original installation used parallel 500 kcm aluminum cables that were 1800 feet long. The cables were damaged and were going to be replaced with parallel 350 kcm copper cables. If will be very difficult to change the aluminum cables in their entirety, so it was decided to install an adequately sized junction box at the 1000 foot mark. There are two options being considered:
Option 1 - Install a power block with 4 ports per phase in the junction box. Each port would be properly sized and rated for either copper or aluminum conductors. This would result in the two 1000' long copper conductors being in parallel, and then that combination would be in series with the parallel combination of the two 800' long aluminum conductors per phase.
Option 2 - Install a mechanical crimp reducing splice sleeve in each conductor. Each side of the splice sleeve would be properly sized and rated for each conductor type and size. This would result in two 1800' long conductors (1000'copper and 800' aluminum) being placed in parallel per phase.

My question is: Which option (or do both options) comply with NEC 310.15(H)(2)or other NEC requirement that I have not considered?
310.15(H)(2)states: "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; and
5) Be terminated in the same manner."
What do you think?
Thank you,
Podo

 

[waross]

Check with your local inspector. His decission is all that matters.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Notwithstanding Bill's comment, all of the criteria would be satisfied in either scenario. They are referring to the PARALLEL conductors, nothing about series.

I would propose doing it with the junction box if it were me. It affords some future person the ease of changing out the remainder of the Al conductors later if necessary.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[melspuds]

As Bill stated first check with AHJ. The only NEC problem that I see is changing wire size without OCP at the junction of 500kcm Al to 350kcm Cu. The amperage is about the same, but the difference in the cable size. I would think best thing to do, use 500kcm Cu instead of the 350kcm Cu. That would also help with any voltage drop and allow for larger motor load in the future. Do not connect the phase two parallel sets together. Keep one Al cable and one Cu cable per splice only. When paralleling cables the only two places allowed are at being and end of the parallel run.
Hope this helps and good luck,
Dave

 

[podobing]

Since I have a few responses, here is my concern:
Option 1 - A 1000' copper conductor is being paralleled with another 1000' copper conductor. No problems with any of the 5 NEC requirements listed above.
A 800' aluminum conductor is being paralleled with another 800' aluminum conductor. No problems with any of the 5 NEC requirements listed above.
These two paralleled sets are then but in series. No problems.

Option 2. A 1000' copper conductor is put in series with an 800' aluminum conductor. No problem.
Another 1000' copper conductor is put in series with another 800' aluminum conductor. No problem.
When these two "hybrid" conductors are placed in parallel, I feel that is a direct violation of 2) Consist of the same conductor material, and 3) Be the same circular mil area.

I understand that what is important is what the AHJ thinks, not what I think. But before I approach anyone, I wanted some other opinions.

Thanks,
Podo

 

[flexoprinting]

Hi Podo

Maybe not an option for your company but we had additional transformer and switch gear installed on the other side of our building way more convenient.

Chuck

 

[podobing]

Chuck,
There is no other source of power readily available. This area is on top of coal storage silos, and the cable(s) that were damaged run in cable tray on top of the inclined conveyor that feeds the first silo. The problem with changing the entire cable is working with a cable tray that goes from the top of one silo, over top of a transfer belt, to the top of a second storage silo. That is why splicing is a safer option. The power is fed from an MCC at the base of the inclined conveyor.

Dave,
The ampacities of the different cable types are about the same, and are far greater than the motor ampacity requirements. Voltage drop using the two cable types is within NEC recommendations.
I agree with splicing better the way to proceed, I just want to make sure that the splicing is done in an approved manner.
Podo

 

[Parchie]

@Podo,
May we know how your cables got damaged? Was it electrical in nature or a mechanical damage? My quick calcs tell me your voltage drop using 2 x 500MCM cables was around 6% for a 1,800 feet run. Replacing with smaller cables will result to a bigger voltage drop at the motor terminals, IMO.
I would agree with using 1000 MCM if you don't have tight turns on your cable run.