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    Single Conductors

    Let's get the critics out of the way first... I am an electrical engineer with an additional degree in electrical construction, as well as time spent in the trade. I would never design or construct an unsafe environment for anyone and the following question is to serve as an educational tool only.

    My boss came to me and asked a simple question which no one seems to have truly answered. Where does the code explicitly state that single conductors such as THHN, THWN, etc., must be run in conduit?

    I know the first person will answer.. NEC 300.3(A) "(A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3." And even 310 says the same thing... But as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method", as side from subject to physical damage, prohibits a single conductor to be run say in a wall or other open spaces freely? You can buy single conductors marked "direct burial" in which case conduit is not required... so where is the line drawn? I would like a documented code, standard, something concrete other than "because thats the way we do it" response, please... if possible.

    Back story, the topic came up because we are on a job where the building was up graded and we found the service entrance cable in a crawl space under the upgrade, breaching through a layer of item-4 and then diving back down in. No sign of conduit on either end. At the meter, there was a conduit sub up.

    #2
    Originally posted by Rock86 View Post
    My boss came to me and asked a simple question which no one seems to have truly answered. Where does the code explicitly state that single conductors such as THHN, THWN, etc., must be run in conduit?

    I know the first person will answer.. NEC 300.3(A) "(A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3." And even 310 says the same thing... But as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method", as side from subject to physical damage, prohibits a single conductor to be run say in a wall or other open spaces freely?
    Take a look at Article 394.

    -Hal

    Comment


      #3
      There isn't a chapter 3 wiring method called "thhn conductors through bored holes in framing members"

      I don't think there is any reasonable argument for single conductors in walls being "directly buried"
      Ethan Brush - East West Electric. NY, WA. MA

      "You can't generalize"

      Comment


        #4
        Originally posted by electrofelon
        There isn't a chapter 3 wiring method called "thhn conductors through bored holes in framing members"
        Art 394 but I'm not trying to agree with these guys.

        Originally posted by Rock86
        But as my boss and I discussed after reading through Chapter 3 carefully, what "recognized wiring method"...prohibits a single conductor to be run say in a wall or other open spaces freely?
        Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3.

        It's not like this is a bad translation from Chinese. "Recognized wiring method" doesn't prohibit anything. "Shall only be installed" is what does.

        Plain English to me. Both of you need to read it again.

        -Hal

        Comment


          #5
          Originally posted by hbiss View Post

          Art 394 but I'm not trying to agree with these guys.
          Yeah I was also going to say, "....other than 394 as Hal said which is very restrictive"
          Ethan Brush - East West Electric. NY, WA. MA

          "You can't generalize"

          Comment


            #6
            Thanks guys! (Ladies, gentlemen, others... whatever you choose just using guys as a general term so don't shoot me),

            394 was our only go to as well, but if you use the phrase "Knob and Tube" you're bill automatically becomes the cost of a new house hahaha.

            I guess I was hoping for something a little more solid. And yes "shall only be installed" is plain English, but the interpretation what wiring method it shall be installed by seems to be our thought. I'm not saying loosey goosey is a recognized wiring method.

            Comment


              #7
              I think the key phrase here is, "wiring method." What does that mean? For example, if I take a #12 THHN, attach a lug to one end, and screw it onto a terminal block, is that a "wiring method"? If I take the same wire, this time without a lug, and wrap the end around the terminal of a switch and then tighten the screw, is that a different "wiring method"? Or does that phrase refer to how wires are routed from one place to another? For example, are running one set of conductors in EMT and another set of conductors in PVC different "wiring methods"?
              Charles E. Beck, P.E., Seattle
              Comments based on 2017 NEC unless otherwise noted.

              Comment


                #8
                Originally posted by Rock86 View Post
                394 was our only go to as well, but if you use the phrase "Knob and Tube" you're bill automatically becomes the cost of a new house hahaha.
                Knob & Tube can't be used in new construction.

                Originally posted by Rock86 View Post
                I guess I was hoping for something a little more solid. And yes "shall only be installed" is plain English, but the interpretation what wiring method it shall be installed by seems to be our thought.
                Any of the wiring methods in Chapter 3 of your choosing that you would run individual conductors with. Tubing and all the various types of conduit are available, for example. Obviously the cables already have the conductors within them.

                -Hal

                Comment


                  #9
                  Perhaps>>>


                  Chapter 9 Tables

                  (9) A multiconductor cable, optical fiber cable, or flexible
                  cord of two or more conductors shall be treated as a
                  single conductor for calculating percentage conduit or
                  tubing fill area. For cables that have elliptical cross
                  sections, the cross-sectional area calculation shall be
                  based on using the major diameter of the ellipse as a
                  circle diameter.
                  ~RJ~

                  Comment


                    #10
                    Originally posted by romex jockey View Post
                    Perhaps>>>

                    For cables that have elliptical cross
                    sections, the cross-sectional area calculation shall be
                    based on using the major diameter of the ellipse as a
                    circle diameter.

                    ~RJ~
                    Which makes 3-cond UF in conduit a particularly crappy combination.
                    Master Electrician
                    Electrical Contractor
                    Richmond, VA

                    Comment


                      #11
                      Originally posted by LarryFine View Post

                      Which makes 3-cond UF in conduit a particularly crappy combination.
                      JMHO...depends on if 'raceway' or 'sleeve' .....




                      ~RJ~

                      Comment


                        #12
                        Why the 2 NMs in the Smurf tube? Unless there's no drywall going up I don't see the need...

                        Comment


                          #13
                          Originally posted by PaulMmn View Post
                          Why the 2 NMs in the Smurf tube? Unless there's no drywall going up I don't see the need...
                          Exsposed NM is like old people at the beach in tight swimsuits, strictly speaking there it's not against the law but nobody wants to see that.
                          If Billy Idol is on your playlist go reevaluate your life.

                          Comment


                            #14
                            Originally posted by Rock86 View Post
                            we found the service entrance cable in a crawl space under the upgrade, breaching through a layer of item-4 and then diving back down in. No sign of conduit on either end.
                            The above installation is in violation of 2017 NEC 300.5(C) and 300.5(D)
                            one could reach for 110.3(B) 'service entrance cable' is listed in the UL white book:
                            SERVICE-ENTRANCE CABLE (TYLZ)
                            GENERAL
                            Types USE and USE-2 — Indicates cable for underground installation
                            including direct burial in the earth. Maximum size is 2000 kcmil. Cable in
                            sizes 4/0 AWG copper, aluminum or copper-clad aluminum and smaller
                            and having all conductors insulated is suitable for all of the underground
                            uses for which Type UF cable is permitted by the NEC. Multiconductor
                            Type USE cable contains conductors with insulation equivalent to RHW or
                            XHHW. Multiconductor Type USE-2 contains insulation equivalent to
                            RHW-2 or XHHW-2 and is rated 90°C wet or dry. Single- and multicon-
                            ductor Types USE and USE-2 are not suitable for use in premises. Single-
                            and multiconductor Types USE and USE-2 are not suitable aboveground
                            except to terminate at the service equipment or metering equipment.
                            Both
                            the insulation and the outer covering, when used, on single- and multi-
                            conductor Types USE and USE-2, are suitable for use where exposed to
                            sun.


                            Originally posted by charlie b View Post
                            I think the key phrase here is, "wiring method." .../snip/...are running one set of conductors in EMT and another set of conductors in PVC different "wiring methods"?
                            Yes I think so.

                            To completely answer the question though, you could go to probably the first wiring 'method' in the code 'open wiring on insulators' ART 398, now only allowed for industrial or agricultural establishments.

                            Comments based on 2017 NEC unless otherwise noted.

                            Comment


                              #15
                              Originally posted by romex jockey View Post
                              Perhaps>>>



                              ~RJ~
                              This doesn't answer single conductors NEEDING to be run in conduit, but it was a good thought.

                              Comment

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