Table 310.15(B)(6) for Parallel Service

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Bjenks

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I have a customer who is wanting to run a parallel set of 4/0 XHHW to handle a 350A calculated residential service load. He is quoting Table 310.15(B)(6) as 4/0 Al for 200A so he multiplied that times 2 and got 400A. I believe that there is no such thing as paralled feeds when using Table 310.15(B)(6) right? I feel bad as he has already ran it as he was trying to save money over my specified copper single run of 400 kCMIL. I couldn't find in the code where it says or equivalent CM, only the gage of wire. I am hoping there is something in there to let him use it.
 
I agree with your view, however I think we can find code making panel statements that say that table can be used to size parallel conductors.
 
Read the text for T310.15(B)(6), and you will see the words '3-wire'. If you ran 6 wires, do you still have a 3-wire service?
 
One more: Table 310.15(B)(6) is based on the NEC 220 and not the breaker size right? so a panel calculation of 110A could be protected by a 125A breaker. I ask this because the customer put a XHHW-2 on the feeder to each dwelling unit using a #1 in which I normally would have put 1/0, but once again he is telling me that is works with the next size up rule.
 
480sparky said:
Read the text for T310.15(B)(6), and you will see the words '3-wire'. If you ran 6 wires, do you still have a 3-wire service?
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NEC 2008 said:
For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors,
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I would think if they are truely parallel conductors then the parallel pairs would be considered one conductor.
 
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Dennis Alwon said:
....I would think if they are truely parallel conductors then the parallel pairs would be considered one conductor.....
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Not disagreeing with you, but is there a definitive answer?

If it's considered one conductor, how do you calculate raceway fill?
 
480sparky said:
Read the text for T310.15(B)(6), and you will see the words '3-wire'. If you ran 6 wires, do you still have a 3-wire service?
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Of course you would. The "Number" of conductors as you are describing have no reference IMO to a 3-wire service. 3W service is just single phase with neutral. 4W service would be 3 phase with neutral. How you run a 3wire service is up to the installer parallel or triple etc..
 
480sparky said:
Not disagreeing with you, but is there a definitive answer?

If it's considered one conductor, how do you calculate raceway fill?
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I believe the key is a 3 wire service-- single phase, 3 wire. The podco delivers the 3 wire, sp service to the house.


Raceway fill is a different issue-- although I see your point I don't agree with it.
 
Perhaps I'm mistaken but isn't this a moot point?

AL 4/0 from T310.16 has a value of 180A, in parallel that would equal 360A. This would exceed the calculated load and thus be satisfactory.
 
dana1028 said:
Perhaps I'm mistaken but isn't this a moot point?

AL 4/0 from T310.16 has a value of 180A, in parallel that would equal 360A. This would exceed the calculated load and thus be satisfactory.
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Oh sure .... stop a good discussion with facts. :grin:
 
Dennis Alwon said:
I would think if they are truely parallel conductors then the parallel pairs would be considered one conductor.
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They're not considered one when you apply derating.
 
480sparky said:
Not disagreeing with you, but is there a definitive answer?

If it's considered one conductor, how do you calculate raceway fill?
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Excellent point as there isn't any temperature or bundling derating factor for 31.15(B)(6). I always looked at as a very simple table, either you do it according to the table or you go to 310.16
 
Bjenks said:
I have a customer who is wanting to run a parallel set of 4/0 XHHW to handle a 350A calculated residential service load. He is quoting Table 310.15(B)(6) as 4/0 Al for 200A so he multiplied that times 2 and got 400A. I believe that there is no such thing as paralled feeds when using Table 310.15(B)(6) right? I feel bad as he has already ran it as he was trying to save money over my specified copper single run of 400 kCMIL. I couldn't find in the code where it says or equivalent CM, only the gage of wire. I am hoping there is something in there to let him use it.
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Are you running to (2) two 200amp panels or (1) one 400amp?
 
ceb58 said:
Are you running to (2) two 200amp panels or (1) one 400amp?
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I started to ask the same question but when I read this part I thought it was one panel and a real parallel setup.

I feel bad as he has already ran it as he was trying to save money over my specified copper single run of 400 kCMIL.
Click to expand...
 
Dennis Alwon said:
I started to ask the same question but when I read this part I thought it was one panel and a real parallel setup.
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Now that I reread the OP it may be a real parallel by the reference to one set of 400 kcm.

Man, I had a at-a-boy from Bob and may have blowen it:grin:
 
Dennis Alwon said:
I believe the key is a 3 wire service-- single phase, 3 wire. The podco delivers the 3 wire, sp service to the house.
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Definitly understand your theory but the nec just doesn't explain everything.All one can do is put pieces of other articles together and make a best guess. But in this case two articles would disagree with you. One is...
(2) Adjustment Factors.
Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

and in the not allowed to be used handbook...

Provided a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or feeder conductors that supply the main power feeder to a dwelling unit. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.

Rick
 
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