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how is the barn going Cutter?
We were interesting in getting from a very old 60A service to a house we demolished to a 100A panel on a construction trailer. There is a nearby 14.4KV line that goes through the property and a transformer on that feeds a neighbour and us. What we found is that the difference in cost between 100 and 200A overhead service line is not much. In addition, combination panels that are used for standard residential services are inexpensive compared to anything that isn't used in standard residential construction. We ended up putting a meter and standard 200A panel on a new pole and feeding the trailer underground as a 100A branch circuit. The 200A service will allow us to run branch circuits to outbuildings, and it didn't cost much more than a 100A service. A surprisingly costly item was 30' of direct burial 100A copper. Around here, to run underground, direct burial cable has to be used. For a branch circuit, the use of conduit is optional, and almost anything can be used. The main reason for using conduit is that the cable can be replaced without digging up an entire trench. At least here, the conduit isn't waterproof--in fact it probably can't be since a 12" below trench floor frost loop is required. I've used DB2 conduit ass required for 200A service line. I've also used 3" drain and even 4" flex drain for branch circuit conduit--all properly inspected. Flex drain should be avoided since wire ends tend to get caught in the corrugations. Maybe there are some limits to the length of a branch circuit line, but the general rule is the wire gauge is increased one step for runs over 100', but I don't know if that rule would cover a 400' run. The idea is that line losses are related to line resistance. Smaller wire, and longer wire has more resistance than larger wire. Using larger wire for long runs costs more to buy the wire, but it produces less line losses and the wire operates at a lower temperature.
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how is the barn going Cutter?
Sounds like that idea worked well for your application Tom. I will probably use 4-0 URD for my run to the building, enclosed in conduit. I chose to go with an uncommon box and switch because I always over-do everything (to the tune of $5oo in material on the pole). All of my projects will surely outlast me. Since I had to take over maintence of the pole and the cables running up and down it, as well as the overhead run to the house, I wanted everything to be as trouble free as possible, including waterproof switchboxes. I have seen numerous installations you have described in the various farm camps in my area. They don't seem to have a problem with that either, but I ams whats I ams. If this did not involve my main residence, I would have gone another route.
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how is the barn going Cutter?
Cutter: I usually do all wiring myself, but in the case of our pole I used a pole contractor. He built the entire pole--panel enclosure, conduit, service entrance cap and even the ground plate and line--at his shop. He came alone with his digging truck and the whole installation on his pole trailer. With a little assistance from me, he had the pole planted in under an hour. It was worth every cent compared to me wrestling with the pole myself.
A couple of things about trenching: Codes often require deeper trenches under drives, but with conduit it's not very desirable to change the trench depth to go under a drive because sweeps would have to be used. However, the use of cable protection, such as cedar planking above the line may reduce the depth requirements. The use of planking under drives may reduce the depth requirements and save a whole lot of digging. I'd sure use oversized conduit and no sweeps if I was pulling 400' of wire by hand, and I'd also probably use DB conduit. The joints on DB conduit aren't glued here, and the joints are designed to be knocked together. I sure wouldn't want the possibility that the joints in drainpipe used for conduit came apart somewhere over 400’. I use drainpipe only for short runs. The good thing about unglued joints is that they come apart so you don't have 400' of continuous pipe if it ever needs to be removed. I'd also dig the trench, assemble the conduit while feeding the pull line through each section, and then I'd backfill only enough short sections to hold the conduit down so the entire trench doesn't have to be dug up if something hangs up while pulling the line. However, there might be a safety issue in having an open trench. Some inspectors want to see an entire trench with conduit assembled and will make a special trip before hook up. Others will allow backfilling except for the working pits at either end—it’s good to check to see what an inspector will allow.
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how is the barn going Cutter?
I like the cedar idea Tom. I do have to cross the driveway, there is an empty unused 4" pe culvert there I can use to insert conduit but it is only six inches or so deep. I will probably have to rip it out and go under it, but I do have the name and number of the inspector so I intend to do a verbal walk through with him. He was very helpfull when I wired my pool. I ran a 60 amp sub feed to my garage, installed a breaker box, wired the pump, my compressor, the outlet for the pool area (required by code) and the light. I also had to follow special grounding guidelines around the decking of the pool. I burried it all 2' deep, which was more than required. My only regret is that I used 1" conduit. The price difference for 1 1/2" would have been well worth the cost for ease of installation. I too have sub-contracted the pole work with the exception that the pole is already there and I am building the backboard. I dislike having to contract what I can do myself, but this feeds the house as well and besides not being and expert on code, the wife would mount me on the pole if I screwed it up.
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how is the barn going Cutter?
I read on one of the electrical boards that it is against code to pull wire through conduit one section at a time. The suggested reasoning was that if you had to pull the original wire through the completed conduit, then you could also pull through replacement wires if necessary.
I would suggest putting some of the "WARNING" red or yellow plastic tape (I think it commonly comes as 3" wide but is available in different widths and messages) several inches above the conduit as you refill the trench. That way someone digging another trench across yours will hopefully snag the warning tape and realize that something is amiss before they dig through your power line.
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how is the barn going Cutter?
Yes, that's true as far as I know, and the idea of coloured tape is a good one. Cable should be pulled through completed conduit. I believe the reason is that there is potential for damage to the cable on the edges of disconnected joints. In addition, gentle bends in trenches are allowed, and the conduit can be jostled around quite a bit in forcing it into slight bends against the trench walls. That's the way I managed to save an apple tree that was on the line for a new service cable. It wouldn't been a good idea to have cable inside the conduit when I was laying it. Setting DB conduit joints also would damage cable in the conduit. Whacking on a wood block over the end the last section with a sledge sets the joints. That can't be done with cable hanging out the conduit end. What I was feeding through one section at a time was 3/8th” poly rope pull-lines.
There is a trick to bending cold conduit in trenches (using DB PVC conduit. I wouldn’t try it with ABS drainpipe). The first trick is to recognize the conduit only tolerates GENTLE bends. Then, the conduit can be blocked away from the trench wall to hold the ends off the wall, and the joints can be set. The conduit expands against the wall when the blocks are removed, and the joints are held securely when the trench is backfilled. Custom bends made by heating the conduit are allowed but are discouraged. Prior approval from an inspector may be required. Curves that are severe enough to require custom bends or sweeps make pulling the line much more difficult and should be avoided if possible. The trouble with heated bends is that long radius curves can't be made, and that makes wire pulling difficult. The radius of a cold bend can be over several conduit sections, and quite a bit of curvature is possible without complicating wire pulling.
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how is the barn going Cutter?
Another relevant code requirement is that if you add up all the bends in your conduit, there cannot be more than 360 degrees between pull points. And the access covers to the conduit system must remain accessible.
Almost all areas are covered by the NEC, although not all reference the same year. Some areas do add additional requirements, however. A handy website that covers some of the high points of the NEC is http://www.codecheck.com
Link:
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how is the barn going Cutter?
I should have mentioned in my post directly above that when you get to the CodeCheck website, scroll down the menu on the left side of the screen to find the electrical (or plumbing, or mechanical) area. If you don't do that, it just looks like a site to sell you their hard cover book - which, by the way, is pretty handy to have around...
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