Parallel Feeders

[gravitydrno]

On a job where the guy doing the underground ran one conduit instead of two for parallel feeders and we now have to run conduit overhead. Have always been taught both runs need to be same length.... How close do they have to be? Is there a percentage to follow? How much leeway do I have?

 

[Cow]

If you're thinking one overhead and one underground, that's not going to work. If you're going to do them both overhead, then run them side by side. That's close enough.

 

[gravitydrno]

Thank you for your reply. I have measured the overhead run and they are really close, 3' on a 90' run. You say it won't work, why? Measurement? That's why I asked percentage? Or for math behind the calculations.

 

[dkidd]

(2) Conductor and Installation 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.
(3) Separate Cables or Raceways. Where run in separate
cables or raceways, the cables or raceways with conductors
shall have the same number of conductors and shall have
the same electrical characteristics. Conductors of one
phase, polarity, neutral, grounded circuit conductor, or
equipment grounding conductor shall not be required to
have the same physical characteristics as those of another
phase, polarity, neutral, grounded circuit conductor, or
equipment grounding conductor.

If one is in a raceway, all have to be.

 

[Carultch]

On a job where the guy doing the underground ran one conduit instead of two for parallel feeders and we now have to run conduit overhead. Have always been taught both runs need to be same length.... How close do they have to be? Is there a percentage to follow? How much leeway do I have?

There is no formal rule about how different they can be in length. By omission, the de-facto rule is that they cannot differ in length by one single inch.

The NEC does not specify that they have to follow EXACTLY the same path, although you are better off if they do. They do have to be the same type of raceway, same conductor metal and insulation, filled with the same number of current-carrying conductors. If the raceways do not follow the same path, be prepared to prove that they are the same length, so have pull string measurements ready.

If they are routed along the same path, and one raceway takes the outside track more often than the other, and thus gains a little extra length, usually no one will think anything of it, and call it a day. Ideally, you would gather a slack loop in the shorter raceway's conductors to make up the difference. But if they are routed along separate paths, it is much more likely to be questioned.

Running one underground, and the other overhead is asking for a challenge. The ambient temperatures of the different environments will affect their respective ampacities. I do not read any direct rule stating that they have to be in the same environment, but this is another reason to doubt its validity. This could be seen as a different "electrical characteristic".

 

[ActionDave]

...Running one underground, and the other overhead is asking for a challenge. The ambient temperatures of the different environments will affect their respective ampacities. I do not read any direct rule stating that they have to be in the same environment, but this is another reason to doubt its validity. This could be seen as a different "electrical characteristic".

Running one underground and one overhead is a clear code violation. 300.3(B)(1)

 

[Carultch]

Running one underground and one overhead is a clear code violation. 300.3(B)(1)

300.3(B)(1) does not directly say that. 300.3(B) says to group all conductors in the same raceway, and then 300.3(B)(1) states that in the case of parallel conductors, you can install them in separate raceways per 310.10(H), and you have to either isolate phases where allowed, or group a complete balance of all phases in each raceway.

Help correct me if I am wrong, but I don't see any rule that specifically states the paralleled raceways have to be grouped. It is what I'd do anyhow, and recommend doing, but I don't see where it is directly required.

 

[ActionDave]

300.3(B)(1) does not directly say that. 300.3(B) says to group all conductors in the same raceway, and then 300.3(B)(1) states that in the case of parallel conductors, you can install them in separate raceways per 310.10(H), and you have to either isolate phases where allowed, or group a complete balance of all phases in each raceway.

Help correct me if I am wrong, but I don't see any rule that specifically states the paralleled raceways have to be grouped. It is what I'd do anyhow, and recommend doing, but I don't see where it is directly required.

Maybe I'm reading it wrong. I am biased by the thinking that when running parallel conductors the goal is to keep everything as close to the same as possible and that would include staying in the same trench for both sets of conductors.

 

[dkidd]

Help correct me if I am wrong, but I don't see any rule that specifically states the paralleled raceways have to be grouped. It is what I'd do anyhow, and recommend doing, but I don't see where it is directly required.

I think that you have a valid analysis.

 

[augie47]

As questionable as the install would be, I don't see where its a violation to run one overhead and one underground.

 

[petersonra]

As questionable as the install would be, I don't see where its a violation to run one overhead and one underground.

while I don't "like" it, I am inclined to agree it is not a code violation in itself.

 

[ActionDave]

What about 300.5 (I) ex No. 1? Doesn't it say all the conductors have to be underground even if you use separate raceways.

 

[augie47]

I'm not reading that in (I). Very well may be mistaken, but I still don't see the violation.

 

[ActionDave]

I'm not reading that in (I). Very well may be mistaken, but I still don't see the violation.

I may be wrong too. I didn't read anything till after I shot my mouth off then I started to look into more.

300.5 (I) combined with Excel. No 1 to me says that you have to be in the same trench but you don't have to be in the same raceway.

 

[texie]

I may be wrong too. I didn't read anything till after I shot my mouth off then I started to look into more.

300.5 (I) combined with Excel. No 1 to me says that you have to be in the same trench but you don't have to be in the same raceway.

300.3(B)(1) Exception is referring to an isolated phase installation which is different than what the OP is doing.

As for the OP situation, I don't think it meets code as the electrical characteristics of the the 2 runs would be very different, even if the same type of raceway was used, and thus would not comply with 310.10(H)(2). I can't imagine any AHJ allowing this.

While we don't know the sizes involved with the OP, in some cases the math can workout to put all conductors in the 1 raceway that he has.