Seperation of conduits in trench

[wawireguy]

Is there any code, building, NEC or otherwise that calls for seperation of PVC conduit being buried in a trench for low volt runs, fire, alarm, telephone, cable?

On the same note is there any code that calls for seperation of 120/208/240/277 runs in PVC in a ditch?

I couldn't find anything myself...

 

[chris kennedy]

Is there any code, building, NEC or otherwise that calls for seperation of PVC conduit being buried in a trench for low volt runs, fire, alarm, telephone, cable?

On the same note is there any code that calls for seperation of 120/208/240/277 runs in PVC in a ditch?

I couldn't find anything myself...

Nope, might want to check with you local utilities.

 

[dicklaxt]

Chris I have only run across the Plant Stds dictating such and mostly when they do its from IEEE doc's that are pretty strict allowing spacing based on voltage levels as well as current draw from less than 50ma to 800 amp plus and voltaghes from 12VDC to 15KV plus

dick

 

[chris kennedy]

Although separation is not NEC required, I still maintain some. Here the 4 conduits on the bottom are POCO laterals and the 4 on top are phone cable.

View attachment 2040

 

[sandsnow]

Although separation is not NEC required, I still maintain some. Here the 4 conduits on the bottom are POCO laterals and the 4 on top are phone cable.

View attachment 2040

Actually separation is required. It is a poorly written section since no guidelines are present to as to how much separation is required.

The explanation in the handbook is joke.

310.15(B)(2)(b)

 

[charlie b]

Actually separation is required.

Not quite. It is "spacing" that must be maintained, not "separation." If you have one inch between conduits, then keep that one inch throughout the run. If you have conduits touching, then keep them touching throughout the run. Establish your desired spacing, then maintain that spacing. There is no minimum amount of spacing that is required.

 

[tkb]

How does the fill between the layers of conduits get compacted without damaging the upper layer of conduits?

 

[chris kennedy]

How does the fill between the layers of conduits get compacted without damaging the upper layer of conduits?

Its sugar sand here. We back fill to the top conduits, rinse it in then add another lift when the first settles.

 

[sandsnow]

Not quite. It is "spacing" that must be maintained, not "separation." If you have one inch between conduits, then keep that one inch throughout the run. If you have conduits touching, then keep them touching throughout the run. Establish your desired spacing, then maintain that spacing. There is no minimum amount of spacing that is required.

Charlie, you're right. I misread that.

This section being where it is, I would think the concern is heat transfer between conduits just like in bundled MC Cables.

So if theoretically I can start with zero spacing, then whats the point of any spacing at all?

 

[charlie b]

I think it is not so much the transfer of heat amongst the conduits, but rather the uniformity of that heat transfer as you go along the run. If the conduits are close to each other for (let us say) 10 feet, then are a foot apart for the next 10 feet, then are four feet apart for 20 feet, then are close to each other for the next 30 feet, and if this uneven spacing goes on throughout the run, then the risk is that some portion of the run will get hotter than the others. Thus, even if the ampacity limits are not exceeded (and you might need an engineer to calculate the ampacity), you may still have a problem with insulation damage in one section of the run.

 

[cowboyjwc]

I get this question a lot. The only code that talks about pipes being seperated is the plumbing code (potable water and sewer).

Another question I get is, "when we pour the concrete over the conduits, does it have to be red?" Since the concrete's not required, it can be any color you want.

I was always taught that you kept a seperation between the phone and/or cable tv and the electrical because you would get "noise" on the phone or cable, but I don't think that is a problem so much anymore.

 

[sandsnow]

I think this came in for the 1999 NEC. I'm going to put this on my list of things to do and get the ROP/ROC on it. Gotta get my money's worth on that NFPA membership

 

[wawireguy]

Appreciate the response! Great information!