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Thread: Digging a trench for electrical

  1. #1
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    Default 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.

  2. #2
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    Default 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

  3. #3
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    Default 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

  4. #4
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    Default 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 Images Attached Images
    Last edited by Frank Pellow; 11-05-2011 at 11:10 AM.
    Cheers,
    Frank

  5. #5
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    Default 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.

  6. #6
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    Default 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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    Default 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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    Default 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.

  9. #9
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    Default 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!"

  10. #10
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    Default 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.
    http://forum.canadianwoodworking.com/image.php?type=sigpic&userid=12450&dateline=127309  6828 Wood Wreck - Structural framing specialist.

  11. #11
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    Default 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

  12. #12
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    Default 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.

  13. #13
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    Default 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 at 11:05 PM.
    Kevin

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    Default Re: Digging a trench for electrical

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

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    Default Re: Digging a trench for electrical

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

    Brian
    " It is nice to be important but more important to be nice"

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    Default Re: Digging a trench for electrical

    In Ontario the electrical is a provincial entity and unless you have applied for an electrical permit they will not take your call. completely separate from the municipal building inspectors. I think they may have a web site that you can submit a question but have never gone that route.

    Brian
    " It is nice to be important but more important to be nice"

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    Default Re: Digging a trench for electrical

    just remember to put a pull rope in the pipe. Put something heavy on the end of the rope and run it through each pipe as you assemble them. It easier this way than trying to fish it later. If you do put in 2" you could use a shopvac to suck a sponge through with baler twine tied to it.
    Pete

  18. #18
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    Default Re: Digging a trench for electrical

    The biggest problem with Electricians is you must ask them the right questions to get the answer you can use.

    I had 4 electricians over to give me a quote to get power from the house over to my garage shop. All 4 of them measured, and went off. 3 were never heard from again. The 4th quoted $5000. It was a bit too steep for me, so I just hired him to install the new 200amp panel.

    While waiting for the hydro crew to disconnect the power from the house so that they could start, i asked him if there was anything that they could do to help bring the price down. Like just connect the panel and a single 120 and 240v plug just to get power in there. I'll use and extension cord. Then I asked if we run the power under the deck, rather than around the side of the house, would that drop the cost. He responded, "sure we can do that, and then you don't need to dig as long a trench. That will bring the cost down". ?? HU ?? why didn't you suggest that from the start??

    Then today, I was talking with my father about digging the trench myself, and he asked me, why don't you just run a conduit along the garden wall beside the driveway? If you were running power to a new location in a business, that's the way you'd do it.

    So I phoned up the electrician to see if that was even possible, and was told 'sure, just didn't think you wanted to do that. Would be a lot cheaper too'. Arrg!

    If only i could find an electrician who wasn't rolling in money, and was willing to provide these less expensive solutions, I could have had it all done by now. I'm back to waiting now for yet another quote and seeing when he can fit this now less expensive job in.

    Matt.

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    Default Re: Digging a trench for electrical

    Quote Originally Posted by matt.mackinnon View Post
    The biggest problem with Electricians is you must ask them the right questions to get the answer you can use.

    If only i could find an electrician who wasn't rolling in money

    Matt.
    Hardly fair... I don't believe it matters what line of work you're in. If the cilent asks for something, you do your best to provide it. Maybe you should have asked for the cheapest possible scenario, rather than state how you'd think it could be done. As far as guys not coming back..., well if there's not enough to made, why would they...?

  20. #20
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    Default Re: Digging a trench for electrical

    Quote Originally Posted by J. Vibert View Post
    Hardly fair... I don't believe it matters what line of work you're in. If the cilent asks for something, you do your best to provide it. Maybe you should have asked for the cheapest possible scenario, rather than state how you'd think it could be done. As far as guys not coming back..., well if there's not enough to made, why would they...?
    I didn't say to any of the people, that I want it done a particular way. My point was more along the line of the one guy that came back to me, did so with the most expensive solution, and no dialogue to me about any alternative options. With any job that you quote on, you need to consider that there is a chance that if you quote too high that you just might not get any work at all as you priced yourself out of a job.

    I guess I must have a different view on what is considered a major job, and what is not. If converting a panel from 100amp to 200amp, running a 110' 100amp line from the new panel to a garage, and then wiring the garage up with new lights, and outlets is considered small, then how does someone who just wants a new electrical plug installed ever get it done?

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