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Old 05-14-2012, 09:40 PM   #1
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Default Parallel Conductors

The NEC 310.4 (A) states that conductors in parallel should be the same length and the same conductor material. . . i thought i knew that rule and how to aplly it, but doing some reading oer the weekend put some doubts in me. I read that the above mention rule aplies to a "parallel set". . now here's where the terminollogy gets in the way. . what do you call a parallel set?. . . are each individual phases and grounded conductor consider a "set" or you consider a set all the conductors in the same conduit a set?
I always thought that one set was the phases and grounded conductor in the same raceway. . .
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Old 05-14-2012, 09:45 PM   #2
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To me and the intent of the rule AS II UNDERSTAND IT, is the set should be all the A phase conductors same length or as nice to the same length as possible.
All the B phase conductors same length or as nice to the same length as possible.
All the C phase conductors same length or as nice to the same length as possible.

And the same goes for the neutral and GECs if pulled (I would think)
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Old 05-14-2012, 09:51 PM   #3
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I was on a job and we terminated a parallel run.

All A phase were the same length to their lug.

All B phase were the same to the lug (but slightly longer then a phase)

All C phase were the same to the lug. ( but slightly longer then b phase)

However B phase and C phase were longer then A (as the lugs are seperated by a couple inches)

The inspector interpreted this as a violation as all the wires were not the exact same length. He made us redo the work.

Hope that made sense.
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Old 05-14-2012, 09:51 PM   #4
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I agree with Brian and will add you could have 100' long copper A, a 115' long aluminum B and and copper or aluminum of a different size for C.
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Old 05-14-2012, 09:54 PM   #5
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Quote:
Originally Posted by al13nw4r3LC76 View Post
The inspector interpreted this as a violation as all the wires were not the exact same length. He made us redo the work.
Wow, that sucks and was the wrong call by the inspector.
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Old 05-14-2012, 09:54 PM   #6
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Quote:
Originally Posted by brian john View Post
To me and the intent of the rule AS II UNDERSTAND IT, is the set should be all the A phase conductors same length or as nice to the same length as possible.
All the B phase conductors same length or as nice to the same length as possible.
All the C phase conductors same length or as nice to the same length as possible.

And the same goes for the neutral and GECs if pulled (I would think)
So if i have two raceways each having 4 conductors ,( phase A, phase B phase C ,and grounded conductor) i should aplly that rule to the phases and grounded conductors like for example :

Phase A - 2 250 Kcmil AL , 105 ft long
Phase B - 2 3/0 cu , 106 ft long
Phase C -2 3/0 cu, 103 ft long
Neutral Set - 2 1/0 AL 104 ft long

This set up should be fine as long as the rule is interpreted the same way. . .Right?
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Old 05-14-2012, 09:57 PM   #7
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Quote:
Originally Posted by al13nw4r3LC76 View Post
I was on a job and we terminated a parallel run.

All A phase were the same length to their lug.

All B phase were the same to the lug (but slightly longer then a phase)

All C phase were the same to the lug. ( but slightly longer then b phase)

However B phase and C phase were longer then A (as the lugs are seperated by a couple inches)

The inspector interpreted this as a violation as all the wires were not the exact same length. He made us redo the work.


Hope that made sense.
so it's one of them rules that the last word belongs to the inspector and his interpretation.
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Old 05-14-2012, 09:59 PM   #8
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Quote:
Originally Posted by BBQ View Post
I agree with Brian and will add you could have 100' long copper A, a 115' long aluminum B and and copper or aluminum of a different size for C.
Even if they are in different raceways?
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Old 05-14-2012, 10:00 PM   #9
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Quote:
Originally Posted by charlie Bob View Post
so it's one of them rules that the last word belongs to the inspector and his interpretation.
Only if you don't fight it.
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Old 05-14-2012, 10:01 PM   #10
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Originally Posted by charlie Bob View Post
Even if they are in different raceways?
Sure but you would probably never do that. All 3 phase conductors must be in the same raceway. There are only a few instances when you can run phase "A" in one conduit, and the other phases in different conduits.
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Old 05-14-2012, 10:03 PM   #11
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Quote:
Originally Posted by charlie Bob View Post
Even if they are in different raceways?
Yes.

The only conductors that must be the same are the conductors of the same phase, neutral or ground.
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Old 05-14-2012, 10:12 PM   #12
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Here is the wording from the 2011


Quote:
310.10(H)

(2) Conductor 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
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Old 05-14-2012, 10:17 PM   #13
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Quote:
Originally Posted by Dennis Alwon View Post
Sure but you would probably never do that. All 3 phase conductors must be in the same raceway. There are only a few instances when you can run phase "A" in one conduit, and the other phases in different conduits.
I meant have one phase a conductor, one phase b conductor , one phase c conductor and one neutral conductor per raceway Dennis, . . that's where the terminology confused me, i consider that a "set". . i was wrong.,. . .
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Old 05-14-2012, 10:18 PM   #14
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Quote:
Originally Posted by Dennis Alwon View Post
Sure but you would probably never do that. All 3 phase conductors must be in the same raceway. There are only a few instances when you can run phase "A" in one conduit, and the other phases in different conduits.
The utility told an EC that all A had to be in one conduit, All B in one conduit......About 1-1/2 years later we got the emergency call. Was a nice repair 3000 amp service 600 kcmil 100' long. The customer operated on generator until the repair was made,
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Old 05-14-2012, 10:19 PM   #15
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Quote:
Originally Posted by al13nw4r3LC76 View Post
I was on a job and we terminated a parallel run.

All A phase were the same length to their lug.

All B phase were the same to the lug (but slightly longer then a phase)

All C phase were the same to the lug. ( but slightly longer then b phase)

However B phase and C phase were longer then A (as the lugs are seperated by a couple inches)

The inspector interpreted this as a violation as all the wires were not the exact same length. He made us redo the work.

Hope that made sense.
Did you ever confront him about it ?
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Old 05-14-2012, 10:23 PM   #16
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Quote:
Originally Posted by brian john View Post
The utility told an EC that all A had to be in one conduit, All B in one conduit......About 1-1/2 years later we got the emergency call. Was a nice repair 3000 amp service 600 kcmil 100' long. The customer operated on generator until the repair was made,
having that set up created that serice call? . . .where all the raceways the same materials?
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Old 05-14-2012, 10:24 PM   #17
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Quote:
Originally Posted by brian john View Post
The utility told an EC that all A had to be in one conduit, All B in one conduit......About 1-1/2 years later we got the emergency call. Was a nice repair 3000 amp service 600 kcmil 100' long. The customer operated on generator until the repair was made,

What right did the utility have to do that? If they made me I would sure as hell got them to sign something. Now it can be done underground with PVC-- I believe Bob has an install done that way.300.3(B)(1) exception
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Old 05-14-2012, 10:25 PM   #18
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Did you ever confront him about it ?
My journeyman at the time told me I had done the job wrong. Telling me the inspector was right. I was a second year at the time. Having come from resi I didn't understand why I was wrong but was shown the code section and it seemed funky to me but the shop I worked for was happy to redo it. To the inspectors liking.
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Old 05-14-2012, 10:28 PM   #19
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the way the 2011 is worded it sounds like all the conductors from all the sets have to be the same length. I don't have the handbook - anyone know if it clarifies it ?
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Old 05-14-2012, 10:33 PM   #20
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Quote:
Originally Posted by Dennis Alwon View Post
What right did the utility have to do that? If they made me I would sure as hell got them to sign something. Now it can be done underground with PVC-- I believe Bob has an install done that way.300.3(B)(1) exception
The EC asked for input, this facility had 3 buildings 3 services first two were PVC With all All A, all B and all C in separate conduits as the made the parallel tie in easy I guess? The third (the one that was damaged ) were in Rigid. Not sure how or why the utility was involved in the decision making.

And before anyone ask, all scrap went to the customer.
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