Intent of 310.15.B.2.b

[kpepin]

What is the exact intent of Art 310.15.B.2.b?

(b) More Than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained.

If I run 2 4" Conduits side by side do I need to keep 4 1/2" between them? I have always installed conduit with about 1 1/8" between them. This way I can use a short piece of 3/4" rigid between them to get the same spacing and I can always get a strut strap on the conduit.

If this is wrong, let me know. I think the code should use a dimension in this article because, to me, it's a bit vauge.

 

[charlie b]

Re: Intent of 310.15.B.2.b

You are right, it is vague. I would also like to see that paragraph clarified. I think this is one area in which it will not be easy for the code-makers to reach a consensus.

My interpretation is that it does not matter how far apart you install the raceways. Just keep the distance between them as close to constant as you can reasonably achieve. Don?t have them one half inch apart for 20 feet of a run, and three feet apart for the next 20 feet of the run, and then five inches apart for the next 40 feet of the run.

Absent any guidance from the code, I go back to basic physics. Such an installation would have the various sections of the run characterized by different values of mutual inductance and capacitance. The same current going through the entire run would cause greater heating in some areas, and less heating in other areas. This could lead to degradation in the insulation system, and it would be both hard to predict and hard to detect. The simple way to prevent the problems is to forbid that type of installation. So I would tell you to keep them one and one eighth inches apart for the entire run (again, as close as you can reasonably achieve), and you would satisfy the code.

 

[kpepin]

Re: Intent of 310.15.B.2.b

I see where I was confused. I was mistaking a period for a comma when I was reading it. I thought it was saying that I had to keep 1 conduit space between conduits.

It looks like it might say consistent spacing between conduits, or just not to have them touching each other. I think it can be taken either way. This one should be cleared up a little.

 

[charlie]

Re: Intent of 310.15.B.2.b

I have never paid any attention to that statement. The following is from the NFPA NEC Handbook.

Spacing is normally maintained between individual conduits in groups of conduit runs from junction box to junction box because of the need to separate the conduits where they enter the junction box, to allow room for locknuts and bushings. Field experience has indicated this degree of spacing between runs has not caused any problems.