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Definition of 'Solid Rock' 300.5 Ex. 5

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    Definition of 'Solid Rock' 300.5 Ex. 5

    Greetings all
    We had a backhoe operator digging a trench say " I hit solid rock can't trench any deeper", a seasoned Electrician went out there and sad ‘yep’ and installed PVC pipe, and the contractor planned to encase it in 2" of concrete. Inspector said its not 'solid rock' its ‘layered rock’.

    It got me wondering what is the legal definition of 'Solid Rock' as used in 300.5 Ex. 5?

    Thanks in advance
    Comments based on 2017 NEC unless otherwise noted.

    #2
    I know in most construction contracts “solid rock” requires drilling, blasting, or rock hammers to remove.
    Im not an inspector but I would say the man on the backhoe is a better judge of what his equipment will remove and what he considers solid rock.
    Any definition leaves some ambiguity, as not all definitions are the same.

    Comment


      #3
      I agree with @Hv&Lv. What does the inspector care as long as it's installed in a Code compliant manner? It's not like you are asking for an exception.

      -Hal

      Comment


        #4
        Originally posted by hbiss View Post
        I agree with @Hv&Lv. What does the inspector care as long as it's installed in a Code compliant manner? It's not like you are asking for an exception.

        -Hal
        In some places there would be barely 3" of cover, its pretty remote rocky terrain, the inspector says the exception can only be used where 'solid rock' is encountered, so therefore a code violation...
        It had just rained pretty heavy before the inspector was there and the trench was muddy and the rock was not clearly visible. I demonstrated with a large metal digging bar that it was solid rock.

        Yeah @Hv&Lv that makes sense and will be helpful in making an argument.
        Comments based on 2017 NEC unless otherwise noted.

        Comment


          #5
          Originally posted by tortuga View Post

          It had just rained pretty heavy before the inspector was there and the trench was muddy and the rock was not clearly visible.
          So how does he know that it was "layered rock" if he couldn't see it? I don't know how you could settle this other than having him there while your backhoe operator tries to break it up.

          I remember being on a job where they actually had a blasting contractor (who was on the site anyway) blast maybe ten feet of rock for a service. I seem to recall there would be about 3" of cover above the rock also.

          -Hal
          Last edited by hbiss; 09-14-19, 01:49 AM.

          Comment


            #6
            Just my opinion but if you cannot dig it with a backhoe then it's solid rock. If the guy digging was using a hand shovel then maybe the inspector would have an argument.
            Rob

            Moderator

            All responses based on the 2017 NEC unless otherwise noted

            Comment


              #7
              Wouldn't "layered rock" be a geological definition of how it formed? Why should NEC care? I think the point NEC intended is if it will be difficult to trench through it they have given you other possible options.
              I live for today, I'm just a day behind.

              Comment


                #8
                I guess "layered rock" would be shale, at least around here. A big excavator can usually rip it out. If the distance isn't that great you might be able to jack hammer a channel through it. If you have something like granite (which is very common also) only way is to blast, or a rock splitter.

                Problem is who gets to decide how much money you have to throw at this?

                -Hal

                Comment


                  #9
                  Thanks again for the replies! There are some pretty rocky places out here, and that confirms my view. Its interesting how quite a few dollars could revolve around a simple interpretation.
                  https://upload.wikimedia.org/wikiped...2404920%29.jpg
                  Comments based on 2017 NEC unless otherwise noted.

                  Comment


                    #10
                    To me, "solid rock" means not crumbled rock. If there is one rock bigger than the hole, or wider than the trench, it's solid rock.

                    How does the inspector know the rock is layered? What would make it solid to him?

                    Rigid metal conduit allows only 6" cover without an exception.
                    Master Electrician
                    Electrical Contractor
                    Richmond, VA

                    Comment


                      #11
                      Originally posted by LarryFine View Post
                      To me, "solid rock" means not crumbled rock. If there is one rock bigger than the hole, or wider than the trench, it's solid rock.

                      How does the inspector know the rock is layered? What would make it solid to him?

                      Rigid metal conduit allows only 6" cover without an exception.
                      I agree, do we really need to call in a geologist if the backhoe won't go through the rock?
                      Rob

                      Moderator

                      All responses based on the 2017 NEC unless otherwise noted

                      Comment


                        #12
                        I encountered solid rock one time driving a ground rod.

                        As I was driving it, it made a complete U when it hit the rock, came up behind me and poked me in the rear.

                        JAP>

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                          #13
                          Sounds like you were between a rock and a hard place.

                          -Hal

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                            #14
                            Actually between a rock and "soft" place.

                            JAP>

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