Parallel Conductors and Conduit

[winnie]

Jon,
I don't think that we are talking about an isolated phase installation here.

Understood. If this is not an isolated phase installation then I completely agree, the conduit must be run in a similar fashion in order to maintain similar characteristics.

The way I read the original post and the post by TCN was that your interpretation is a given (that if all phases were present in all conduit, then all the conduit would need to be routed together), and that the real question was 'could we get around this requirement to keep everything together by running isolated phases?'.

Would you agree that in an _isolated_ phase installation you can have different conduit characteristics?

Based upon my understanding of the original question, I was trying to answer what would be required to permit an isolated phase installation, and also suggesting that even if it was code, it would still be a bad idea.

-Jon

 

[jwjrw]

Understood. If this is not an isolated phase installation then I completely agree, the conduit must be run in a similar fashion in order to maintain similar characteristics.

The way I read the original post and the post by TCN was that your interpretation is a given (that if all phases were present in all conduit, then all the conduit would need to be routed together), and that the real question was 'could we get around this requirement to keep everything together by running isolated phases?'.

Would you agree that in an _isolated_ phase installation you can have different conduit characteristics?

Based upon my understanding of the original question, I was trying to answer what would be required to permit an isolated phase installation, and also suggesting that even if it was code, it would still be a bad idea.

-Jon

That was what I wanted to say but couldnt get it out. It seems it has to do with which way you run your conductors.

 

[don_resqcapt19]

Understood. If this is not an isolated phase installation then I completely agree, the conduit must be run in a similar fashion in order to maintain similar characteristics.

The way I read the original post and the post by TCN was that your interpretation is a given (that if all phases were present in all conduit, then all the conduit would need to be routed together), and that the real question was 'could we get around this requirement to keep everything together by running isolated phases?'.

Would you agree that in an _isolated_ phase installation you can have different conduit characteristics?

Based upon my understanding of the original question, I was trying to answer what would be required to permit an isolated phase installation, and also suggesting that even if it was code, it would still be a bad idea.

-Jon

I guess the code would permit the remote routing of one or more of the isolated phase conduits, and I missed that point in the thread. There would be a lot of pitfalls in the installation such as any ferrous metal that encircled one of the raceways and there would be strong magnetic fields that could cause problems with some equipment.

 

[Team-MEI]

2008-NEC
300.3 Conductors
(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 310.4. 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 392.8(D).
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).

 

[Team-MEI]

2008-NEC
300.5 Underground Installations.
(I) Conductors of the Same Circuit. All conductors of
the same circuit and, where used, the grounded conductor
and all equipment grounding conductors shall be installed
in the same raceway or cable or shall be installed in close
proximity in the same trench.
Exception No. 1: Conductors in parallel in raceways or
cables shall be permitted, but each raceway or cable shall
contain all conductors of the same circuit including equipment
grounding conductors.
Exception No. 2: Isolated phase, polarity, grounded conductor,
and equipment grounding and bonding conductor
installations shall be permitted in nonmetallic raceways or
cables with a nonmetallic covering or nonmagnetic sheath in
close proximity where conductors are paralleled as permitted
in 310.4, and where the conditions of 300.20(B) are met.

 

[winnie]

There would be a lot of pitfalls in the installation such as any ferrous metal that encircled one of the raceways and there would be strong magnetic fields that could cause problems with some equipment.

Reading another thread ( http://forums.mikeholt.com/showthread.php?t=122435 ) I realized that the isolated phase installation being discussed is in fact not possible.

I had been making the claim that if all the rules about having conductors in separate conduit were met, then the installation would be allowed. But I neglected to consider the EGC.

This is a feeder, and thus must have an EGC. An EGC would need to be present in each conduit, and all EGCs would need to be tied together. Since each EGCs would be magnetically coupled to each conduit, I would expect high currents to circulate in the various EGCs associated with this feeder.

-Jon

 

[TCN]

Thanks folks. I joined this forum because I've always appreciated Holt's material and hope to better myself through my peers. You don't disappoint!
I must admit, Dennis points right to it. I feel a bit silly now.:roll: Good show!