Anybody run power cable above ground in conduit?

   / Anybody run power cable above ground in conduit? #1  

s219

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I have been wanting to run power to my barn for lighting. I have 250' of #6 direct-bury aluminum wire that I bought a couple years ago, first to use as an extension cord while building the barn, and it's been used for other projects several other times.

Long term I had planned to trench to the barn and bury the wire, but the direct path to the barn goes through some fairly thick forest in an area that I can't clear due to wetlands environmental restrictions (the indirect path goes through my septic field which I'd rather not trench through). I had to run power to my pier through similar land, and let me tell you it was a real struggle trenching through/around trees and brush and dealing with tree roots. I am not anxious to do that again.

I have studied code and it's allowable to run power cable through conduit above ground as long as it's mechanically fastened to a "structure" of some sort. Fences count as structure, as would posts spaced out every so often. That's a project that could also be a pain in the butt, so I am weighing all the evils of trenching versus running conduit above ground. But it might be easier to use conduit and go above ground. The main downside I can see is that if a tree ever fell over the conduit, it would likely break and need a repair. Otherwise, the conduit would be in the woods out of the way, and over time would get covered up by pine straw and leaf litter.

The funny thing is, I have used that wire as an extension cord to the barn several times, sometimes for 5-6 months at a clip. The wire was just laying on the ground. All perfectly OK with the building inspector. I probably already have a couple years worth of time on the wire for "temporary" use, and now suddenly it gets more complicated when considering how to make it permanent. Maybe I ought to just call it an extension cord indefinitely....:laughing:
 
   / Anybody run power cable above ground in conduit? #2  
The biggest problem I see is pulling it around bends. Aluminum is larger in physical size, less flexible, and the cable version is pretty stiff. You may reach the max pull tension real fast and stretch it. Stretching reduces the cross section and reduces the ampacity accordingly. 250' is a long run so intermediate hand-holes/pull boxes will be required. Plan one at each 90 degree change in direction and use plenty of veener slickum and you will probably make it OK. Remember Aluminum ampacity is less than copper, for #6 it is 10A. Actual ampacity varies according to the type of insulation. You need the table from the Code to determine ampacity. 250' also introduces the voltage drop situation which also changes the ampacity depending on what can be tolerated.

LOL, Ron
 
   / Anybody run power cable above ground in conduit? #3  
Hard to see how setting posts every 4-6' would save time or money. Having been in the construction industry my entire life I've seen several attempts at a "better mouse trap". It seems we always end up back at wood frames- or in this case buried electrical. I'd also hate to look at an above ground conduit- especially one I installed. Code has some options with regards to depth based on pipe and cover material. I'd take advantage of those options in the Wooded area if things got tough.
If your property has true federally designated wet lands I'd go around or over that. I also wouldn't trench through my leach field.
The other option is to set some poles and go overhead.
Btw- with the proper equipment and operator, a 250' conduit trench should take about 4 hours to dig.
Also alu wire is more prone to corrosion and degradation. Make sure the insulation is and remains intact.
 
   / Anybody run power cable above ground in conduit? #4  
Do you really have direct-burry Al wire or do you have direct-burry Al cable?

Direct burry cable (several insulated wires all in one sheath), especially if you have used it as an extension cord is probably more common. I don't think code allows you to put direct burry cable in conduit.

#8 copper wire has the same ampacity as #6 Aluminum wire and a cursory look at the home depot website shows that it is $127 for a 500 foot roll of #8 copper. . You would need 3 conductors plus a ground for 240 volt service. The ground could be # 10. I expect that you might be looking at ~ $250 worth of wire to do this with copper wire pulled in conduit.

Personally, I would look at the #6 copper at $188 for 500 feet. This would add capability for some service outlets, which will come in handy sometime in the future.

The other thing to look at is the new LED lights available now take much less current, and seem to get less expensive every day. Maybe #8 copper and LED lighting is enough.
 
   / Anybody run power cable above ground in conduit? #5  
I definitely recommend the new LED tube lighting. As far a cable/wire sizing I would wire for some expansion. Right now you are thinking of lighting but later on you might want capability to run machinery, welder, heat, whatever.

As far as extension cords... you don't want to hear my 'temporary' 22Ov cord running from my dryer outlet outside and above ground to my detached garage/shop. :eek: :ashamed:
 
   / Anybody run power cable above ground in conduit? #6  
Btw- with the proper equipment and operator, a 250' conduit trench should take about 4 hours to dig.

I had the pleasure of digging a hundred and sixty foot trench to drop conduit into this weekend. In the past I've used a small wheeled walk behind trencher, this time I rented a Toro Dingo with a trencher attachment and there is no comparison. The dingo has tracks and you just pointed it where you wanted to go and let it rip. If it found a rock it might stop the chain trencher, but all you had to do was lift the boom and it would pull the rock up to the surface so you can kick it out of the way and keep going. It also had enough weight and traction that's just rocks and roots and stuff didn't move it out of its path it might have moved over an inch or so but nothing like the walk behind wheel trenchers I've used in the past where you had to manhandle it and fight with it just to get it to go in a straight line and make an actual ditch. The price was the same for the dingo as a walk-behind trencher and I would not go back to a walk behind wheeled trencher if I had any other option.

Aaron Z
 
   / Anybody run power cable above ground in conduit? #7  
When I put in the #8 wire for my camper, the run under ground was only about 100 feet but I knew I wouldn't be able to pull the stiff cable thru the conduit so I dug the trench, the slid each PVC section of pipe over the cable individually to then glue it to the mating one. It took a little time to slide each section of pipe over the entire wire run but when the 90 ell at the end came up, I only had a short section to go and the 90 was easy to run the cable thru for the 4 feet of cable that I had left to go.
I think this approach for your conduit might work also and no need for cable lube especially if you use 10 foot joints of conduit.
 
   / Anybody run power cable above ground in conduit?
  • Thread Starter
#8  
Do you really have direct-burry Al wire or do you have direct-burry Al cable?

Direct burry cable (several insulated wires all in one sheath), especially if you have used it as an extension cord is probably more common. I don't think code allows you to put direct burry cable in conduit.

#8 copper wire has the same ampacity as #6 Aluminum wire and a cursory look at the home depot website shows that it is $127 for a 500 foot roll of #8 copper. . You would need 3 conductors plus a ground for 240 volt service. The ground could be # 10. I expect that you might be looking at ~ $250 worth of wire to do this with copper wire pulled in conduit.

Personally, I would look at the #6 copper at $188 for 500 feet. This would add capability for some service outlets, which will come in handy sometime in the future.

The other thing to look at is the new LED lights available now take much less current, and seem to get less expensive every day. Maybe #8 copper and LED lighting is enough.



This stuff is "triplex" underground distribution cable -- the individual conductors have black polyethylene insulation and are intertwined without an outer jacket. It's rated for direct burial or use inside conduit and the insulation even has UV rating (I assume mainly so that it can be stored outdoors, as it's not intended for exposed/overhead use). It's very versatile. I used similar stuff, albeit non-intertwined and 1/0 AWG, when running cable for my generator because it was rated for so many different types of use. The insulation is tough and smooth, so it pulls very nicely through conduit.

I originally chose the #6 wire because it could carry an honest 120V load over the distance without too much voltage drop, and that worked out great for building/construction use. I don't think we ever tripped the breaker once, even with saws and compressors in use.

I definitely want to use LED lighting now that the prices have come down. That would leave me plenty of margin on the circuit to run something else if needed. Most likely would be a skil saw or miter saw once and a while.
 
   / Anybody run power cable above ground in conduit?
  • Thread Starter
#9  
I should mention that another possible option is to run a new meter from the nearby transformer (that I paid about $2-3K to have installed when we built our home). That is about 200' from the barn. There are some trenching challenges there to, but it would be the power company's concern, not mine. I don't know what the cost would be, if any. I imagine for the foreseeable future, I'd be hitting the minimum bill requirement for the barn since I doubt the power usage will be very high just for lighting and occasional tool use (I have a separate shop attached to my house where most work gets done, so the barn won't see much of that).
 
   / Anybody run power cable above ground in conduit? #10  
In the long run, trenching and running the cables in conduit will be the least hadaches.
 
 
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