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Electrically shocking

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  • Electrically shocking

    I would like some info on why I am getting electrically shocked though my BP handles.
    I have a rotary phase converter, which I built, and with the converter running and the machine motor off, I can feel that funny little "buzz" through the handles.
    Today I got bit really bad when I reached for a wrench laying on the drill press table. The drill was not even plugged in.
    I have a 4 foot grounding rod drove into the ground and the power supply line is grounded through it. The mill sets on a very heavely constructed wooded platform, until I can get the cash to have concrete poured. I do not have the machine base itself grounded and probably should. But I don't see why that would keep me from getting "buzzed" though the handles.
    Any thoughts would be nice.....

  • #2
    Martin: if you have used a 3ph motor for your rotary phase converter, you may want to check the condition of the winding insulation. It could be breaking down and electricty is leaking to ground. To check the insulation, you will need to find some one with a megger. An other thing you may need more grounding rod, depending on the soil. Here in Or. it is hard to get a good ground. As I remenber, to be up to code they recure 3 grounding rods spaced some ft. apart and connected togeather with a continus length of bare copper wire.Hope this has given you some ideas. Some one with more electrical knowledge can help more. Charlie.
    Don\'t ask me to do a dam thing, I\'m retired.


    • #3
      You are getting shocked because your machine is not grounded, and there is some leakage.

      If it IS grounded, leakage will not cause a shock.

      The point of the ground rod is to connect the local "dirt" ground to your green wire (equipment grounding conductor). That way there is no voltage difference between them.

      It must be that your machine switch does not break all three conductors. If one is still connected, the motor won't turn but the motor windings are stll live.

      Please forgive me for the emphasis, but I personally would not touch a machine in your shop until that green wire was run and connected to a local ground rod. And, until the switch shuts off all the live wires for certain.

      I have projects to finish, can't get electrocuted now.


      • #4
        I would make sure there is a continuous unbroken ground conductor all the way back to the NEUTRAL in your service distribution box. This is the box that the power company connects to. I would use #8 or #10 gage wire for this conductor. Dont overlook the value of using GFI devices for all shop circuits. Wayne


        • #5
          Do "they" make a GFI for three phase ?


          • #6
            When I wired my shop,I did it to the code. I bought a used gooseneck light and often got bit by it. Finally dawned on me the two prong plug was wired wrong.Reversed it in the outlet and it stopped tickleing. A GFI,would of kicked out,if I'd had one in that line. You're problem is probably in the motor wiring.But you might check the light,if you have one on the machine.


            • #7
              Ground all machinery directly to a known good ground. Electrical current is lazy, it will take the path of least resistance, if that is through you, and that path includes your heart, you're dead.


              • #8
                It is not enough to just make sure the equipment is grounded. Shock is the feeling you get when the current is flowing from one potential to another through you. So, even if your equipment is grounded, but the ground at the equipment is different than another potential, be that another rod source, or earth, you are at risk of being the path. You need to assure continuity through the service entrance, the source of power to the phase converter, the converter to the machine. If you use any switches or breakers, the ground must be continuous past these.
                My power runs from the house to the shop. the ground is continuous to the sub box in the shop. From the breaker in the shop to the phase converter, the ground is wired through the safety switch to a box in which I have my cap. bank. The ground is common here. From the conveter, I hit a 3 phase safety switch. Again, the ground is wired to and past the switch to the machine. No matter what I touch, the item is commonly grounded to any other item within the shop, hence all are at the same ground potential. This is what you need to strive for. If you make an effort to provide the world's best ground to your mill, in essence, you are causing a potential difference between it and everything else that is grounded differently. Oh, if you can find a knowledgable(sp?)phone person, he/she should have a megger. Also, I went to an electrical contractor, and bought all of my safety switches and enclosures for the mill and converter used for $25. You should be able to open the circuit at any spot. Mike


                • #9
                  If you ae running a single phase system the very first thing you should do is check to see if you have zero pontential between earth (ground) and the neutral conductor in the outlet the equipment is plugged into.

                  If it is more a a few volts you have a "loose neutral" somewhere in your electrical system. This is dangerous as this potential will exist all through a properly wired bulding. The only way to find them is check each and every electrical connection. Any connections with aluminum wires must have electrical wire antioxidant applied to them. and torqued properly or the wires physically twisted together and wire nut tightened to spec. Wrap with electrical tape any hot or neutral splices as well.

                  If the outlet is fine the problem is the phase convertor or the BP electrical circuit and/or motor(s).

                  You may want to check with your local electrical inspector as to code in your area - a GFICB may be required (expensive, but well worth the extra safety measure).


                  • #10
                    Thanks guys,
                    After reading the last 4 or 5 posts, I am questioning the validity of the ground to the shop. This shop was wired over 24 years ago and the cables run underground. I am also wondering if moisture is a problem.
                    I will be checking into the ground line starting at the breaker box.


                    • #11
                      Typically, the neutral is NOT the problem. The equipment ground is.

                      An open neutral on 110 should break the circuit.

                      In this case, the use of a phase converter indicates 220 volt circuit, for which there isn't any neutral needed. It may be there, but it is not used unless a grounded star system is in place, which I doubt.

                      So, the equipment ground is the issue. I mentioned the local ground rod before, and another poster also brought it up.

                      When you touched the drillpress, it might have been grounded by a wire, or it might be grounded by contact with the floor. hard to tell from your description. Since you said the mill didn't have a ground, maybe the DP doesn't either, and the floor is it. No Matter.

                      Bottom line is that if you had a green ground wire (equipment ground) running back to the service box, and a local ground rod connected to it, the following would be true:

                      You would have a good ground sufficient to pop the breaker if you have a hard fault line to chassis on the machine.

                      You would have enough ground obviously to drain away leakage so you should not feel the buzz.

                      You would have the local dirt ground held at about the same potential as the machines. Even if a heavy fault current flowed, with a voltage drop in the green wire, you would not find local dirt ground to be much different from the machines. Safe condition.

                      Evidently this is not the case. I would get that ground put in to code now. Life is short enough already.

                      Oh, and a point of information:
                      with just a local rod, but no green wire back to the service, you may not get the benefits mentioned. Ground rods may have quite a bit of resistance and still be per code.


                      • #12

                        You are of course, correct about the neutral. For some reason I was thinking in terms of 110V cicuits and appologise for my brain damage. Thank you for the correction.


                        • #13
                          I did finally get the rod in a good location and everything is grounded.
                          No longer do I get that buzz.....(boy, could I have some fun with that line...)
                          Thanks to all who gave input.
                          I really enjoyed reading the responses...


                          • #14
                            No more buzz...hey,what fun is that?


                            • #15
                              That is just the kind of buzz you should avoid - anything that ends up with a hospital food hangover...