Secondary Conduit Seperation

[jesse dardis]

Do you know of any NEC code that mentions secondary conduit separation ? I have five conduits that were installed by the builder following different paths. Two of them are 129' & 133'. The remaining three are 103, 105, & 109'. I'm not sure if this will make a difference other than minor calculations ? Thoughts ?

Thank You,

 

[charlie b]

I think you would have a problem with 310.10(H)(2). Although it does not give a specific limit on how closely the length of one conductor must be to the length of another, you are looking at a difference of nearly 25%. That would be, in my opinion, too much of a difference. The issue is that with different lengths you get different values of resistance, and therefore different values of current. One conductor might overheat while another is well below its temperature limit.

Welcome to the forum.

 

[infinity]

What do you mean by a secondary conduit? Are these for 5 sets of parallel conductors?

 

[don_resqcapt19]

Assuming that the length differences are the only thing that will change the current division, and assuming the 5 parallel sets are feeding a 2000 amp circuit, the current division would be approximately 444, 436, 420, 355, and 344 with the shortest run having the most current and the longest one having the least current.

 

[roger]

The builder should have payed an EC to do it.

Roger

 

[petersonra]

Do you know of any NEC code that mentions secondary conduit separation ? I have five conduits that were installed by the builder following different paths. Two of them are 129' & 133'. The remaining three are 103, 105, & 109'. I'm not sure if this will make a difference other than minor calculations ? Thoughts ?

Thank You,

I don't know what you mean by secondary conduits. The code does not require any separation between conduits at all. Code does not require any conduit to be the same length as any other conduit. There is a code requirement for parallel conductors to be the same length but it does not appear to me that the code requires that the conduit the conductors are in have to be the same length

 

[winnie]

There is a code requirement for parallel conductors to be the same length but it does not appear to me that the code requires that the conduit the conductors are in have to be the same length

There is also a code requirement that parallel conductors have the same characteristics, and if you look at things like tables 8 and 9 in chapter 9 it is clear that the conduit changes the characteristics of the conductor. IMHO 150 feet of copper in 140 feet of conduit will have different characteristics than 150 feet of copper in 100 feet of conduit.

-Jon

 

[dkidd]

There is also a code requirement that parallel conductors have the same characteristics, and if you look at things like tables 8 and 9 in chapter 9 it is clear that the conduit changes the characteristics of the conductor. IMHO 150 feet of copper in 140 feet of conduit will have different characteristics than 150 feet of copper in 100 feet of conduit.

-Jon

How would you get 150 feet of wire in 100 feet of conduit?

 

[winnie]

How would you get 150 feet of wire in 100 feet of conduit?

The additional wire would need to be somewhere else, eg. coiled up in the enclosure.

Going back to the original question, there are multiple conduits of different length, presumably for parallel conductors.

I think that as a fix for this petersonra was suggesting that all the conductors could be made up the same length and installed, with the excess conductor simply in the enclosures at the ends of the conduit. IMHO this makes perfect sense for a normal installation, where the conduit will be roughly the same length but could never be exactly the same length, especially when you have to go around a corner.

But in the original question the longest conduit was some 30 feet longer than the shortest. Even if you could find a place to stash the excess 30 feet of conductor (coiled up in the conduit instead of a straight pull????), I claim that the parallel conductors would have different characteristics because of the different conduit length.

-Jon