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  • Yet another wiring question...

    I intend to wire the 2nd mill with the same wiring setup I used for the old mill.

    I have 12/4 dropping down from the disconnect into a 12" x 12" box.
    L1 and L2 with ground to the mill main power switch and on to the VFD.
    In the 12" box I tap off L2 through a 15 amp breaker to power a 110 outlet to run light, DRO and table power feed.
    All grounds connected and neutral goes back to main panel.

    This setup worked fine for years on the old mill.

    Was I just lucky or is this wiring alright?
    Len

  • #2
    I am not an electrician, but it sounds valid to me from a functional point of view.

    Is the 15 amp circuit tied to the input of the disconnect or the output?

    Dan
    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.

    Comment


    • #3
      Branches off the output.

      Also, since I've got 12 wire run to everything including the 110 outlets, would I even need the 15 amp breaker?
      It looks so official sitting on it's DIN rail though.
      Len

      Comment


      • #4
        Originally posted by QSIMDO View Post
        I intend to wire the 2nd mill with the same wiring setup I used for the old mill.

        I have 12/4 dropping down from the disconnect into a 12" x 12" box.
        L1 and L2 with ground to the mill main power switch and on to the VFD.
        In the 12" box I tap off L2 through a 15 amp breaker to power a 110 outlet to run light, DRO and table power feed.
        All grounds connected and neutral goes back to main panel.

        This setup worked fine for years on the old mill.

        Was I just lucky or is this wiring alright?
        I prefer not to wire 110 Vac circuits on top of 220 Vac circuits because of the imbalance that occurs between L1 & L2. I'm not sure what the code says, it's just my personal preference. Since you're using 12/4 your 2 pole breaker should be 20 amp but you don't say what your mill HP is. You're probably okay since you've been doing it for awhile but if it were me I'd give the lights and power feed it's own circuit.

        Ron

        Comment


        • #5
          I do the same thing that Qsimdo does. I have a 220 drop to a disconnect on the mill. I wired L1 and neutral to an auxiliary outlet with a integrated 15 amp fuse. L1 and L2 go from the disconnect to the VFD.

          Ron wrote: "Since you're using 12/4 your 2 pole breaker should be 20 amp"


          Does it really matter? I thought that you could use any circuit protection SMALLER than the capacity of the wire and outlet. You just want it to trip before the wire overheats.

          Dan
          At the end of the project, there is a profound difference between spare parts and left over parts.

          Location: SF East Bay.

          Comment


          • #6
            Dan,

            You're correct about the breaker sizing.

            But if you're powering a milling machine 1, 2 or 3 HP through a VFD plus light/lights and a power feed you're going to want the 20 amps available, especially during heavy cuts. But to put things into perspective, most 12/2, 12/3 and 12/4 cables are protected by a 20 amp single or double pole breakers.

            Ron
            Last edited by nc5a; 09-04-2018, 03:29 AM. Reason: spelling

            Comment


            • #7
              In response to a few of the posters in this thread, there is nothing wrong with tapping off one of the 220V legs for a 110 circuit. When you think about it, by its very nature the 220 feed coming into a residential panel is imbalanced. Each side of the 220 feeds a separate 110 branch in the main distribution panel, and each of those branches are definitely not balanced in terms of actual load, although they would be balanced just in terms of breaker capacity. The only thing I would advise here is that the outlet has its own 15 or 20A breaker...depending on the outlet rating itself, and of course the wiring which I understand to be 12awg. 15A breakers are fine here, and 20A breakers would be the max allowed by code for 12awg.

              Comment


              • #8
                Doing that does have implications.

                You need to make sure the neutral is never disconnected, so pigtailing it is needed. It probably already will have a dual breaker. There are some rules in the NEC for a circuit carrying two hots and one neutral.

                It is also not great to have multiple power sources for one machine, so it is much preferable to power 120V things from the 240V via a transformer, if the machine does not use the neutral.
                2730

                Keep eye on ball.
                Hashim Khan


                It's just a box of rain, I don't know who put it there.

                Comment


                • #9
                  IF you do use a 120v control transformer it is permitted to connect one side of the 120v secondary to the service ground, in order to re-establish a ground referenced neutral.
                  This terminal from the transformer is now deemed a neutral.
                  Max.

                  Comment


                  • #10
                    Originally posted by MaxHeadRoom View Post
                    IF you do use a 120v control transformer it is permitted to connect one side of the 120v secondary to the service ground, in order to re-establish a ground referenced neutral.
                    This terminal from the transformer is now deemed a neutral.
                    Max.
                    Not permitted, REQUIRED. You won’t find this under transformers in the NEC. It is under the heading of Separately Derived Services.

                    Comment


                    • #11
                      Originally posted by garyhlucas View Post
                      Not permitted, REQUIRED. You won’t find this under transformers in the NEC. It is under the heading of Separately Derived Services.
                      Thats odd control cabinetry have used this method for some decades, also NFPA79 shows an exact diagrammatic example of a 120v secondary control circuit set up with a re-grounded neutral.
                      I have also used it for decades in control cabinetry wiring without any inspection problems.
                      Also, look up almost any control equipment wiring diagram.
                      Incidentally if using this method, only the live is fused, otherwise both L1-L2 are both fused.
                      Ah I think I miss read your post as a disagreement in the method, sorry.
                      Max.
                      Last edited by MaxHeadRoom; 09-05-2018, 01:17 PM.

                      Comment


                      • #12
                        Imbalances are normal and quite common. There is an imbalance every time you switch a 115V load on or off: either before the switch is thrown or after or more likely, both before and after. The imbalance in your house or building's system simply changes every time a 115V device is turned on or off. They are the reason for the NEUTRAL wire.

                        It sounds like the OP's wiring is safe and, according to him, it works. Weather it is in complete accord with the NEC and any local codes; I can not say. There are many reasons why additional protections are included in those codes and I doubt that even a 40 year, master electrician knows all of them. If he is really worried, he can request an inspection.



                        Originally posted by nc5a View Post
                        I prefer not to wire 110 Vac circuits on top of 220 Vac circuits because of the imbalance that occurs between L1 & L2. I'm not sure what the code says, it's just my personal preference. Since you're using 12/4 your 2 pole breaker should be 20 amp but you don't say what your mill HP is. You're probably okay since you've been doing it for awhile but if it were me I'd give the lights and power feed it's own circuit.

                        Ron
                        Paul A.
                        SE Texas

                        And if you look REAL close at an analog signal,
                        You will find that it has discrete steps.

                        Comment


                        • #13
                          Also remember the current in the neutral is the lesser difference of L1 L2, not the sum of.
                          Max.

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