1600 amp gear wire size/parallel feed question

mattri

Member
Location
Iowa
Looking to feed a 120/208 3 phase switch gear.

Looking at 310.15(B)(16) it looks as though 750s @ 75* are good for 475 amps. 475x4= 1900, 1900x80% per 310.15(B)(3)(a) is 1520amps.

I really can't see going over 750s, is there any provision for allowing a 500, or at least a 600 in this application?

I know I can't use the next size up OCPD per 240.3(C) but this seems excessive.

Thoughts?
 
The only thing I see is that your 750s are too small.

It is either increasing the size, undesirable IMO, or increasing the amount of sets with smaller conductors.
I agree. As a general rule, rather than trying to minimize the numbers of sets by using the largest possible conductor, use many sets of smaller conductor. The ampacity per area really starts to tank above 350. Depending on the specifics and layout, I would likely not be opposed to running 6 sets for 1600 amps.
 

lauraj

Senior Member
Location
Portland, Oregon
If you have to derate, I'm assuming the load is non-linear, therefore the neutral is counted as a current-carrying conductor.

Let's assume THHN conductors.

1600A/4 parallel = 400amps per conductor.

400A/80% = 500A ---> minimum ampacity required from the 90C column

Looks like you would need 700kcmil.

If the neutral is not a current-carrying conductor, you could use 600's.
 

precise8128

Member
Location
Memphis, TN
I m still learning so correct me if I am wrong: since you are feeding a Switch gear you treat as a feeder @ 100% noncontinuous and not the 83% as you would a service feed...1600awg divided by 4= 400.. 310.16 (2008) 75 degree column
4 pairs of 600 AWG since its good for 420A
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I m still learning so correct me if I am wrong: since you are feeding a Switch gear you treat as a feeder @ 100% noncontinuous and not the 83% as you would a service feed...1600awg divided by 4= 400.. 310.16 (2008) 75 degree column
4 pairs of 600 AWG since its good for 420A

The 83% rule would not be applicable in this application since the voltage is 208Y/120. So if using 4 sets each would need a minimum ampacity of 400 amps as you've stated. For THHN copper that would be a minimum of 600 kcmil. AWG sizes end at #4/0.
 
Looking to feed a 120/208 3 phase switch gear.

Looking at 310.15(B)(16) it looks as though 750s @ 75* are good for 475 amps. 475x4= 1900, 1900x80% per 310.15(B)(3)(a) is 1520amps.

I really can't see going over 750s, is there any provision for allowing a 500, or at least a 600 in this application?

I know I can't use the next size up OCPD per 240.3(C) but this seems excessive.

Thoughts?
For a 1600 amp service I usually design around 5 sets of 400 kcmil. 750 kcmil is extremely expensive and not to mention hard as hell to work with. As far as using the 600 kcmil, I have found that it is not a very common size that the supply hoses carry much of, as well as being very hard to work with.
 

ADub

Senior Member
Location
Midwest
Occupation
Electrician
For a 1600 amp service I usually design around 5 sets of 400 kcmil. 750 kcmil is extremely expensive and not to mention hard as hell to work with. As far as using the 600 kcmil, I have found that it is not a very common size that the supply hoses carry much of, as well as being very hard to work with.
4 is the magic number for paralleled service entries. 300.1 exception 1.


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Cow

Senior Member
Location
Eastern Oregon
I agree with 4 sets of 600 CU. It's worth double checking your lugs first before you commit though.

4 is the magic number for paralleled service entries. 300.1 exception 1.


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I don't see that article in my 2014 NEC.
 

ADub

Senior Member
Location
Midwest
Occupation
Electrician
1600 amp gear wire size/parallel feed question

I agree with 4 sets of 600 CU. It's worth double checking your lugs first before you commit though.



I don't see that article in my 2014 NEC.
My bad 300.3(b)(1) exception

(1) Paralleled Installations. Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.10(H). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with the provisions of 250.122. Parallel runs in cable tray shall comply with the provisions of 392.20(C).
Exception:  Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase installations. The raceways shall be installed in close proximity, and the conductors shall comply with the provisions of 300.20(B).


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iwire

Moderator
Staff member
Location
Massachusetts
My bad 300.3(b)(1) exception

(1) Paralleled Installations. Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.10(H). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with the provisions of 250.122. Parallel runs in cable tray shall comply with the provisions of 392.20(C).
Exception:  Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase installations. The raceways shall be installed in close proximity, and the conductors shall comply with the provisions of 300.20(B).


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Who said this is an underground run?
 

ADub

Senior Member
Location
Midwest
Occupation
Electrician
Who said this is an underground run?
I was responding to knightryder12s post not the op. He said he likes to use 5 sets for services. When we do new services 1600 amp or bigger they're typically ug, actually our utility doesn't give any other options than that. So your question about "this run" is somewhat lost on me, can you elaborate?


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