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  • Digging a trench for electrical

    I am wanting to get a subpannel into my new shop, but it seems that time is against me. I did manage to get 3 electricians in to give me a quote, but non of them want to give me a price. I didn't think it was a small job. I involves upgrading my house panel from 100amp to 200amp and putting the old electric box into the garage with a line run underground between the shop and the garage.

    It's getting closer to winter and the ground is not getting any softer. I am thinking that I'd better get the trench dug myself if I want this done before winter time.

    I know I need to go 18" down and can run a 1 1/2" pipe for 2/4g AL wire. Some have said on another forum that it's better to run 2" conduit.

    That part I have no problem with. But then to meet the code you need to put something above the conduit to give warning about electrical wire. I am not sure what that is, or how to do it.

    There is the rub. I can do the work myself but I don't know what is expected. HELP.

    Matt.
    Matt

    People are like a box of chocolates. It's hard to tell initially which ones are nuts.

  • #2

    Re: Digging a trench for electrical

    Re: Digging a trench for electrical

    We bury electrical lines at work all the time and this is what we use, I would give you a roll but shipping probably would be as much as the tape. Electrical Warning Tape, you should be able to get it wherever you buy your electrical supplies.

    Warning Tape.jpg
    Mike @ Buck Lake

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    • #3

      Re: Digging a trench for electrical

      Re: Digging a trench for electrical

      Also Matt, your electrical line is to have a minimum of 18" of cover as you already know, then backfill the ditch part way so that the underground warning tape is 6" to 12" from the finished grade.
      Mike @ Buck Lake

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      • #4

        Re: Digging a trench for electrical

        Re: Digging a trench for electrical

        Seven years ago when I built my stand-alone woodworking shed, I split 100 amps from my 200 amp service in the house and directed it to the shed. Like you, I dug my own trench then had an electrician install the cable.

        I wrote extensive notes and took lots of pictures on the woodworking shed project and I will extract relevenet material from them about the trench.

        2004 April 18 (Sunday):
        During the last couple of days, I dug about 2/3 of the trench that will eventually be used to run electricity and natural gas to the workshop. This was hard work and the work was not made any easier by the fact that I encountered big chucks of concrete in the ground. It looks the builders of my house must have had concrete left over one day and simply dumped it on the site. A picture is attached showing a cross section of a piece that was about 1.5 metres long.


        Cross-section of concrete in the path of the trench -small.JPG
        I had to break the concrete up with a sledge hammer before I could extract it. Not fun! But, I slept well last night -a little over 10 hours of uninterrupted sleep.

        2004 April 21 (Wednesday):

        Below are two pictures taken today:

        2004-04-23 Trench in foreground, Piers and some building material in background -small.jpg Frank on a pile of extracted clay -small.JPG

        One gives some idea of the mess left behind by the extracted clay. But, the only way to get a real appreciation is to walk in it. Boy is it sticky! I can't recall anything as sticky but the mud in Hearst when I was a kid. I spent about 6 hours today scraping up the clay then wheeling it over to the BIG pile behind the garage. And, I only got about half the job done. The bottom left picture shows the other big contributor to the pile of dirt and mud, namely the almost completed trench. Some of the pile (maybe half) will fit back into the trench once the electricity and gas lines are in, but I reckon that at some point I am going to have to hire someone to come and take away a lot of mud and dirt.

        2004 October 27 (Wednesday):

        Today I re-dug parts of the trench because Mario is coming tomorrow to install the electrical service. I also put up more vapour barrier (now about 90% complete), and more plywood (now about 15% complete).
        A different building inspector came today to check out the siding, the roof, and the insulation. He obviously was impressed with the place and told me: “You should be in construction. I wish that the homes I inspected were built this well.”

        2004 October 28 (Thursday):

        The sub-panel is now installed (upside-down as those in the know will observe) in the shop and one circuit is operational. Here are some photos:

        New sub-panel (Square D) -small.jpg

        Cable in trench -1 -small.jpg Cable in trench -3 -small.jpg Cable in trench -2 -small.jpg


        2004 October 31 (Sunday:

        I partly filled in the trench and put planks over the installation (as required in the Ontario electrical code):

        Wood protecting electrical cable in trench -2 -small.jpg
        Attached Files
        Last edited by Frank Pellow; 11-05-2011, 11:10 AM.
        Cheers,
        Frank

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        • #5

          Re: Digging a trench for electrical

          Re: Digging a trench for electrical

          I would dig down 2' and put in 2 runs of 3" solid pipe. One for hydro and one for future use eg. phone, coaxail, gas, or air line back to the house. As it is not code to run phone lines in the same conduit as hydro.
          "I look to the future because that's where I'm going to spend the rest of my life."
          George Burns

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          • #6

            Re: Digging a trench for electrical

            Re: Digging a trench for electrical

            Definitely go bigger on tire pipe and double up -2 runs if possible. My inspector let me use polyethylene pipe covered with a 2 x 6, but the whole thing is now under concrete. Pulling #6 through 2" is no easy task.

            Don

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            • #7

              Re: Digging a trench for electrical

              Re: Digging a trench for electrical

              I'm just curious Don, how long ago was that? Because at work the electricians haven't put boards in for about the last three years, just the tape.
              Mike @ Buck Lake

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              • #8

                Re: Digging a trench for electrical

                Re: Digging a trench for electrical

                It seems hard to get an electrician, so I guess I'm doing it myself.

                So I dig my trench and put my conduit into it. I'm not sure what I do next. My real concern is to get this dug and laid before the ground gets too cold and hard. We are having frost now.

                I know it will need to get inspected. Do I book that now to get a date, or after the trench is dug. What do I do with the wire? Can I put it in just not terminate it? When do you backfill and put the tape? or wood?

                thanks. I'll be the first to admit that I don't have a clue as to what I am doing, but just need to get it done.
                Matt

                People are like a box of chocolates. It's hard to tell initially which ones are nuts.

                Comment


                • #9

                  Re: Digging a trench for electrical

                  Re: Digging a trench for electrical

                  You could try calling a trenching company. Several companies do what you're needing for new housing.

                  Conduit is a good idea but may not be necessary. Ask the trenchers. They typically lay the lines you require.
                  "Do it Right!"

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                  • #10

                    Re: Digging a trench for electrical

                    Re: Digging a trench for electrical

                    I know it will need to get inspected. Do I book that now to get a date, or after the trench is dug. What do I do with the wire? Can I put it in just not terminate it? When do you backfill and put the tape? or wood?
                    Excuse me if I am missing something, but my experience has been to go chat with the local building department about these very things - they have 8 - 8:30 set aside in the office before their daily field work, to answer any questions. Be sure and note the name or maybe have them initial any applicable sketches and then you have it direct from the horse's mouth, to pardon the expression.

                    They also like this because it slashes their return/reject rate and removes points of contention or ill will after the fact if something was not to their liking. Perhaps you don't want to include them, which is your prerogative of course.

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                    • #11

                      Re: Digging a trench for electrical

                      Re: Digging a trench for electrical

                      Home Depot rents trenchers, I think they're 24" max. If you have a ways to go this would make quick work of it and will save you back.

                      AK

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                      • #12

                        Re: Digging a trench for electrical

                        Re: Digging a trench for electrical

                        Some things to keep in mind...

                        -bigger conduit is better in the world of pulling wire.
                        -18" may be the standard code, but personally I'd go a minimum of 2', and possibly 3' if the digging wasn't too bad.
                        -if your trench crosses beneath a driveway or the like, the ESA will demand you bury your conduit deeper. The weight of the cars/equipment pushes the frost deeper into the soil.
                        -install a second run of conduit for possible communication apps. In this world of wireless everything, you will most likely never use it, but it's worth every penny if the need be.

                        I've seen inspectors ask for the planks or rigid insulation above the conduit in shallow trench installations before. It's just another layer of frost protection. If you're able to dig the extra depth I mentioned earlier, you'll most likely not have to worry about that protective layer.

                        Comment


                        • #13

                          Re: Digging a trench for electrical

                          Re: Digging a trench for electrical

                          You sure the depth of the trenching is frost line issues. I thought in our area being required to go down 4 feet with posts and foundations was the amount that goes just beyond the worst estimated frost line.

                          I had the impression that the depth to lay electrical underground was strictly related to achieving a reasonable depth so as to not be vulnerable to somebody accidentally driving a shovel into it. The additional depth for under driveways and walkways is for the further potential of protection for these areas that are likely digging depths when being repaired/rebuilt using mechanical excavation that is typical for those jobs.

                          I've heard of both for covering the pipe. Even better, but not necessary, would be to bury it in a bed of concrete before topping with the tape and sand. I saw the utility guys doing this once, but it was fibre optic they were burrying.

                          Here's from the simplified code book 1 you can also buy at HD for $20.

                          Electrical Burial Ontario.pdf

                          Here's the more detailed pages from "The Big Book" (simplified book 2) 1998-2002

                          Big Book P1 1998-2002.pdf

                          BB P2.pdf

                          BB P3.pdf

                          BB P4.pdf

                          BB P5.pdf

                          BB P6.pdf

                          The big book is impossible to get to the inner edge of the page, so sorry about the missing parts/edges.

                          If you don't feel 100% comfortable interpreting these rules, get an electrician. Keep in mind also, these pages are puled from old editions of these books, and may have changed. Electrical stuff changes all the time, so don't read these pages as the gospel.

                          Good luck!
                          Last edited by Lost in the Woods; 11-06-2011, 11:05 PM.
                          Kevin

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                          • #14

                            Re: Digging a trench for electrical

                            Re: Digging a trench for electrical

                            2004. I know I didn't use any tape.
                            Don

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                            • #15

                              Re: Digging a trench for electrical

                              Re: Digging a trench for electrical

                              Frank.... you will certainly win the award for the nicest looking trench, good job.

                              Brian
                              If your dreams don't scare you, you are not dreaming big enough

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