Parallel Feeder...

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1793

1793

Senior Member
Location
Louisville, Kentucky
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Inspector
I would like a little help on calculating parallel feeders.

Single family dwelling existing 200 amp service customer would like to move up to 400 amps.

Would I be better off staying with 400kcmil single conductor, Table 310.15(B)(6)or figure parallel runs?

How do I calculate the appropriate conductor for parallel runs?

Table 310.16 4/0 at 90deg. 260 * 80% = 208

Parallel 4/0 THWN/THHN in one 2 ?? conduit for 400 amps?

I look forward to your input.
 
I would go with a single set of 600 CU.....

But that may be overkill for a dwelling unit service.

So my choice for that would be 600 AL

It really does not bend that hard.

It is my opinion that you can not use Table 310.15(B)(6) as a basiss for parrllel runs so if you go parrallel IMO your stuck in 310.16. But not everyone agrees with me on that. :)
 
iwire said:
It is my opinion that you can not use Table 310.15(B)(6) as a basis for parallel runs, so if you go parallel IMO your stuck in 310.16. But not everyone agrees with me on that. :)
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I am among those who do agree.
 
charlie b said:
I am among those who do agree.
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I feel the same which is why I posted the calculations based on Table 310.16. If this service were going to be paralleled what size conductor would you use and why?
 
1793 said:
I If this service were going to be paralleled what size conductor would you use and why?
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Well it is all about the calculated load.

As I don't know the calculated load I will give you my answer for a full 400 amps.

Copper

2 sets of 3/0 in seperate conduits

2 sets of 4/0 in the same conduit

AL

2 sets of 250 in seperate conduits

2 sets of 350 in the same conduit

However with the calculated these would likely be smaller.
 
ptonsparky said:
Must be nice to live an area where you can get stuff. If I went to any of the supply houses within a hundred miles they would say "600 what?"
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I can't even imagine that. :)

600, 750 CU or AL, THHN/THWN, XHHW-2 all usally stock items in this area....at least in the big supply houses.
 
I agree with Bob's answer again (gotta stop doing that!). Actually, I started typing my answer, and noticed that he posted first.

But Bob's answer is about what choices you might have. If your question is about which is the best choice, then I cannot help you. It comes down to cost for materials and labor, and to your ability to install any of the choices in the space available (i.e., concrete sidewalks or other interferences), and the willingness of the owner to tolerate disruption of his or her service for a given length of time, and the terminations available from the utility, and a host of other things that I know nothing about.
 
At least you have the handbook editors on your side Bob:

From the 2005 commentary: "If a single set of 3 wire, single-phase....the reduced conductor size permitted by 310.15(B)(6) is applicable....

Steve
 
1793 said:
I'll bite "Trans S"?
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It's like a Trans Am, but instead of being the AMerican version, it is the Swedish version. Doesn't everybody include the price of a hot new car with each of their bids? :D
 
Check w/ your utility company, but I belive any service over 200 Amps requires a current transformer , aka "TRANS S". You could include the trans am if you want ?????????
 
adavey said:
Check w/ your utility company, but I belive any service over 200 Amps requires a current transformer , aka "TRANS S". You could include the trans am if you want ?????????
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Around here you can get a 300 amp meter pan.
 
Proposal 6-74 in the 95ROP was to prohibit the use of the reduced wire sizes in parallel. Panel 6 rejected the Proposal with this statement: "Conductors 1/0 and larger are permitted to be paralleled by section 310-4. This would apply to Note 3."
In the 93 code the reduced size rule for dwelling unit service conductors was Note 3 to Table 310.16.
Don
 
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