Medium Voltage Feeder

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jbolen

Senior Member
I'm in disagreement with engineer who is trying to tell me. That you can install one phase of 3-phase 30K volt service in seperated conduits.

A-phase in one 4" B-phase in a seperate 4" and C-phase in another 4"

I'm saying they have to be install in same conduit.
 

charlie b

Moderator
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Location
Lockport, IL
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I agree that you can, as Bob mentioned. But I have to wonder why an engineer would want to. The only good reason I can think of for separating the phases is to make it easier to route each phase to the terminations. That might be of benefit to the installer, and that is not a bad reason, but it is unlikely to be the basis for a design decision on the part of the engineer.
 

John Valdes

Senior Member
Location
SC.
Occupation
Retired Electrician
I'm in disagreement with engineer who is trying to tell me. That you can install one phase of 3-phase 30K volt service in seperated conduits.

A-phase in one 4" B-phase in a seperate 4" and C-phase in another 4"

I'm saying they have to be install in same conduit.

That's how we always did parallel conductors. Separate conduits. I was under the impression that it was required? Are we talking parallel? I am asking.
 

don_resqcapt19

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Location
Illinois
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retired electrician
I agree that the code has a specific provision in the exception to 300.3(B)(1) to permit an isolated phase installation underground, however it is my position that the exception is not needed and that the provisions of 300.3(B)(3) would permit isolated phase installations in any location.
 

david luchini

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Connecticut
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I would agree that 300.3(B)(3) would allow isolated phase installations either overhead or underground, for systems 600V or less.

But the OP mentions a 30kV feeder. I'm wondering if 300.35, for system over 600V, allows isolated phase installations per 300.20(B), or would you read 300.35 as requiring you comply with both 300.20(A) and (B)?
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
David,
I skipped right over the 30kV part, but I don't see anything in Article 300, Part II that would prohibit an over 600 volt isolated phase system. Yes, compliance with 300.20 is required, but that does not prohibit an isolated phase installation using non-ferrous wiring methods. Note that 300.20 only applies to ferrous wiring methods and the last part of 300.20(A) that requires "all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together" does not apply to installations using non-ferrous wiring methods.
 

Smart $

Esteemed Member
Location
Ohio
That's how we always did parallel conductors. Separate conduits. I was under the impression that it was required? Are we talking parallel? I am asking.
Don't know if the OP scenario is paralleled, but it is not required for parallel installations. In fact, it is only permitted by exception where installed underground: 300.3(B)(1), 300.5(I).

However, as you inferred, such an installation must be of paralelled conductors (i.e. multiple sets). An installation using only one set of conductors does not qualify for the exceptions.
 

don_resqcapt19

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Location
Illinois
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Smart,
How does the specific exception in 300.3(B)(1) over rule the blanket permission for isolated phase installations that is in 300.3(B)(3)?
 

Smart $

Esteemed Member
Location
Ohio
300.3(B)(3) does not permit isolated phase installations. It states "where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords..." then requires compliance with 300.20(B), and others for MI and MC cable installations. That is not the same as permitting such an installation... it's an "in addition to" requirement. The actual permission is under 300.3(B)(1) and 300.5(I) exceptions.
 

Smart $

Esteemed Member
Location
Ohio
I should add that I know many interpret 300.3(B)(3) as permitting conductors of the same circuit to be run in different non-magnetic sheathed cables... but it doesn't really say that.
 

don_resqcapt19

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Location
Illinois
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retired electrician
I should add that I know many interpret 300.3(B)(3) as permitting conductors of the same circuit to be run in different non-magnetic sheathed cables... but it doesn't really say that.
That is exactly what it says. If it didn't permit running conductors of the same circuit in different non-ferrous raceways or cables, there would be no need for the reference to 300.20.

300.3(B)(1)through (B)(4) are really exceptions to the main part of the rule. There is no need for the exception to (B)(1) as (B)(3) permits the installation covered by the exception.
 

wawireguy

Senior Member
He's probably doing it to make pulling the conductors easier. Might be one conducoter per conduit. Maybe he thinks it will reduce the chance for damage to the conductors. It's probably going from vault to vault so all underground. I recall a thread sometime back where this was permissable.
 

Smart $

Esteemed Member
Location
Ohio
That is exactly what it says. If it didn't permit running conductors of the same circuit in different non-ferrous raceways or cables, there would be no need for the reference to 300.20.

300.3(B)(1)through (B)(4) are really exceptions to the main part of the rule. There is no need for the exception to (B)(1) as (B)(3) permits the installation covered by the exception.
No, it does not say that. Perhaps that is the intent, I don't know... But I do know the words do not explicitly support such an intent.

That said, please show me in 300.3(B)(3) where permission is granted. 300.3(B)(1) and its Exception, (2), and (4) each contain the words "shall be permitted". 300.3(B)(3) does not.
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).
(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 392.10(M).
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).
(2) Grounding and Bonding Conductors. Equipment grounding conductors shall be permitted to be installed outside a raceway or cable assembly where in accordance with the provisions of 250.130(C) for certain existing installations or in accordance with 250.134(B), Exception No. 2, for dc circuits. Equipment bonding conductors shall be permitted to be installed on the outside of raceways in accordance with 250.102(E).
(3) Nonferrous Wiring Methods. Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with the provisions of 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with the provisions of 330.31, 330.116, and 300.20(B).
(4) Enclosures. Where an auxiliary gutter runs between a column-width panelboard and a pull box, and the pull box includes neutral terminations, the neutral conductors of circuits supplied from the panelboard shall be permitted to originate in the pull box.
 

don_resqcapt19

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Illinois
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retired electrician
Again we have to agree to disagree. If (B)(3) does not permit this, then there is no reason for (3)(B) to be in the code as it would not do anything.
 

don_resqcapt19

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Location
Illinois
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retired electrician
NFPA 70 ? May 2001 ROC ? Copyright 2001, NFPA

3- 12 - (300-3(b)): Reject
SUBMITTER: Wayne A. Lilly, Bridgewater, VA
COMMENT ON PROPOSAL NO: 3-11
RECOMMENDATION: This proposal should be accepted.
SUBSTANTIATION: The Panel Statement did not address the issue raised in the proposal substantiation regarding (b)(3). This section was revised at the comment stage during the 1999 Code cycle. The revision included a new concept that should not have been accepted because it did not have the benefit of public review. The new concept is given in item three. It is now possible to obtain conductors from separate nonmetallic or nonmagnetic sheathed cables or raceways to form a circuit. Please review the comments given in the proposal substantiation again. The proposed language for 300-3(b) is simplified, direct, and easily understandable. It also does not introduce any new material. Thank you for your consideration.
PANEL ACTION: Reject.
PANEL STATEMENT: While there may be some validity to the submitter's substantiation, there is no technical reason why wiring methods employing a nonferrous outer jacket or sheath should not be permitted to be installed as separate cables where the cables are run in close proximity to each other. Since the nonferrous outer jacket or sheath is nonmagnetic, these cables would permit cancellation of magnetic lines of flux from one cable to another. Care must be used where installing these cables to insure the cables are not separated by any ferrous metal products and obviously where entering a ferrous metal enclosure, they must comply with Section 300-20. Aluminum MC cable and nonmetallic sheathed cable are two cables types that could utilize this method of installation.
This action correlates with the action by CMP-7 on Proposals 7-126 and 7-126a allowing single conductor such as nonferrous MC cable with the same requirements as existed for MI cables where single conductor MC cable is used.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 11
VOTE ON PANEL ACTION:
AFFIRMATIVE: 11
 

Smart $

Esteemed Member
Location
Ohio
Again we have to agree to disagree. If (B)(3) does not permit this, then there is no reason for (3)(B) to be in the code as it would not do anything.

...
PANEL STATEMENT: While there may be some validity to the submitter's substantiation, there is no technical reason why wiring methods employing a nonferrous outer jacket or sheath should not be permitted to be installed as separate cables where the cables are run in close proximity to each other. Since the nonferrous outer jacket or sheath is nonmagnetic, these cables would permit cancellation of magnetic lines of flux from one cable to another. Care must be used where installing these cables to insure the cables are not separated by any ferrous metal products and obviously where entering a ferrous metal enclosure, they must comply with Section 300-20. Aluminum MC cable and nonmetallic sheathed cable are two cables types that could utilize this method of installation.
This action correlates with the action by CMP-7 on Proposals 7-126 and 7-126a allowing single conductor such as nonferrous MC cable with the same requirements as existed for MI cables where single conductor MC cable is used.
...
I am not in total disagreement with you, for I believe the intent to permit circuit conductors in more than one non-ferrous, non-magnetic raceway or cable is a viably safe wiring method. All I am saying is the wording of (B)(3) does not give explicit permission to do so. At best, one has to consider it as inferred by inclusion.

Furthermore, a couple issues, also mentioned in the PANEL STATEMENT you posted, are not addressed in (B)(3) wording. The issues are the circuit conductors should [must?] be installed in close proximity to each other, and also that no ferrous material separate the circuit conductors. These are major issues in safe wiring regardless of intent, and the wording of (B)(3) does not cover these issues (for other than MI cable) nor is it covered in this regard anywhere else for other than at enclosures. As such, and under the premise (B)(3) permits isolated circuit conductors, we can run the conductors any distance apart (except MI), without any consideration for any magnetic material between the circuit conductors...!!!

I should also note that my intent on posting is in regard to your original contention that, essentially, there is no need for (B)(1) Exception.
Smart,
How does the specific exception in 300.3(B)(1) over rule the blanket permission for isolated phase installations that is in 300.3(B)(3)?
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
I stand by my statement that the exception is not required and the isolated underground installation is permitted by (B)(3), we do however need (B)(1) to permit parallel installations in ferrous wiring methods.

As far as the conductors permitted by (B)(3) passing through ferrous metal that is covered by 300.20(B). I know that that section is intended to apply to the conductors where they enter the enclosure, but I think you can take a broad reading of the first sentence of 300.20(B) and say that it applies to any ferrous metal that surrounds or encircles a conductor.

You are correct that it does not address the proximity of the cables to each other, but the code does not currently address the hazard of high magnetic fields, so is that really a safety hazard, assuming that 300.20(B) is complied with?
 

Smart $

Esteemed Member
Location
Ohio
I stand by my statement that the exception is not required and the isolated underground installation is permitted by (B)(3), we do however need (B)(1) to permit parallel installations in ferrous wiring methods.

As far as the conductors permitted by (B)(3) passing through ferrous metal that is covered by 300.20(B). I know that that section is intended to apply to the conductors where they enter the enclosure, but I think you can take a broad reading of the first sentence of 300.20(B) and say that it applies to any ferrous metal that surrounds or encircles a conductor.

You are correct that it does not address the proximity of the cables to each other, but the code does not currently address the hazard of high magnetic fields, so is that really a safety hazard, assuming that 300.20(B) is complied with?
Let it suffice to say the current wording does not exhibit the full extent of intent in some ways, and perhaps redundant in others. ;)
 
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