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  • More Grounding Questions

    I should probably be asking these questions in a electrical forum but I usually get easier to understand answers here. : )

    First... Why do you need a ground if your main panel has the neutral and ground wires all connected together?

    Second... It is my understanding that If you run a sub panel off your main breaker box the grounds and neutrals MUST be separated because if you tie neutral to ground in a subpanel, you're created a potential parallel path for current and now everything that you've grounded to that sub-panel is hot.

    IF the above is correct, why isn't this also true when the ground and neutral are tied at the main service panel?
    Polyoxybenzylmethylenglycolanhydride

  • #2
    You need them separated at all other points because you don't want the ground to carry any current UNTIL it is the fault path. But you need that fault path to carry fault current immediately and sufficiently to trip the circuit breaker.

    Having the neutral and ground be parallel paths, doesn't make the ground "hot" because the neutral is not "hot." Hot is the conductor that has the working voltage. The neutral is a CCC (current-carrying conductor), but is not "hot." The ground is at practically the same electrical potential as the neutral, but is not a CCC.

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    • #3
      I'll give it a try

      It is a circuit and the power is always returning to where it was generated.
      Regular 120-v Circuit: Power comes down the Hot leg and then returns on the Neutral. All good no problems.
      hmmm... What IF we have a problem?

      What if there is an overload? Ahh, we add a CB that can sense that too much power is going through it.

      What if a hot wire comes loose and touches a conducting material?

      ahh, lets add another wire as a safety path. The safety path has to get the power back to its source so we bond it with the Neutral and the main panel and then it uses the Neutral back to the transformer then back down the Hot wire through the CB which senses too much power- opens and interrupts the power.

      NOTE: the ground being connected to earth has no part in this. The fault is going back to the source- Circuit.



      Subpanel:

      If you bond at the sub panel the fault has too many paths it can take back to the source because now, it can travel down any Neutral wire on its way to the main panel bonding post and up to the transformer.

      You want the path to be a direct path so we separate the Ground and Neutral and the ground fault can happily travel on its own wire system.


      Clear as mud?








      Ed Conley
      Screaming Broccoli, Inc
      http://www.screamingbroccoli.net/
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      • #4
        Originally posted by Broccoli1 View Post
        ...NOTE: the ground being connected to earth has no part in this. The fault is going back to the source- Circuit...
        Very good point to make sure gets mentioned and understood.

        A welding "ground" is also different from both. English is awesome.

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        • #5
          Originally posted by Broccoli1 View Post
          I'll give it a try

          It is a circuit and the power is always returning to where it was generated.
          Regular 120-v Circuit: Power comes down the Hot leg and then returns on the Neutral. All good no problems.
          There is where I am getting lost.... The power RETURNS back on the Neutral. Mac says the neutral is not hot. How can it not be hot if the electricity is flowing back on it? How does it just follow the neutral line and not energize the ground when they are all tied together?
          Polyoxybenzylmethylenglycolanhydride

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          • #6
            The typical household hot is 120 V to the neutral. The hot is also 120 V to the ground. Neutral and ground are 0 V to each other.

            Are you familiar with the steam cycle? Or pressurized plumbing versus drains?

            Think of the "hot" as the pressurized water lines, and the neutral as the drain, which has no pressure, yet is the purposeful pipe to let water flow on its way back down to the sewer/reservoir/supply. Think of the ground as the overflow drain which goes to the same place.
            Last edited by MAC702; 01-15-2020, 05:50 PM.

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            • #7
              Originally posted by MAC702 View Post
              The typical household hot is 120 V to the neutral. The hot is also 120 V to the ground. Neutral and ground are 0 V to each other.

              Are you familiar with the steam cycle? Or pressurized plumbing versus drains?

              Think of the "hot" as the pressurized water lines, and the neutral as the drain, which has no pressure, yet is the purposeful pipe to let water flow on its way back down to the sewer/reservoir/supply. Think of the ground as the overflow drain which goes to the same place.
              OK, I get that but an overflow drain is always higher than the regular drain and water goes down the first chance it gets. How does voltage "know" which one is which? Is there something about the neutral that attracts it away from going to the ground or does it just not matter which path it takes?

              Polyoxybenzylmethylenglycolanhydride

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              • #8
                Originally posted by Nipper View Post

                OK, I get that but an overflow drain is always higher than the regular drain and water goes down the first chance it gets. How does voltage "know" which one is which? Is there something about the neutral that attracts it away from going to the ground or does it just not matter which path it takes?
                Mac and the others can correct me, but I think part of the problem is that you are thinking in DC and talking about AC. In DC, the ground and neutral do perform comparable functions, but in AC, the neutral is part of the circuit. (Please correct me. if I am also confused.).

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                • #9
                  In DC, like on a car, the chassis ground is part of the circuit.

                  I didn't know if it would help or hurt, so didn't bring this up yet, but the neutral is actually called the "grounded conductor" because it is the current-carrying conductor that is at ground potential. It's only technically a "neutral" when, as the grounded conductor, it's carrying the unbalanced portion of multi-pole loads.

                  So a typical 120 V household receptacle has a "ungrounded conductor (hot)" a "grounded conductor (neutral)," and an "EGC: equipment grounding conductor (ground)."

                  On the water drain analogy, don't look at the overflow in terms of where it is, but what it does. Normally, it's never used. But if the drain were clogged (there is a fault), the overflow takes the water to the main drain instead of the normal drain doing it. Or, instead of an overflow, think of the ground as the floor drain. If the sink breaks, so water can't get to its drain, the water falls on the floor instead, and the floor drain (ground) takes over. But the sink drain and the floor drain are both at zero pressure (no voltage).

                  Only the neutral is connected to the load. The ground is connected to the chassis. It won't see current unless there is a fault that causes the chassis to become energized by the hot or broken neutral.
                  Last edited by MAC702; 01-16-2020, 05:42 PM.

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                  • #10
                    Originally posted by MAC702 View Post
                    Only the neutral is connected to the load. The ground is connected to the chassis. It won't see current unless there is a fault that causes the chassis to become energized by the hot or broken neutral.
                    So you're saying the neutral and ground are tied together in the main panel but not on the device being powered? In other words the neutral wire on the device will not have continuity with the ground lug or wire?

                    Polyoxybenzylmethylenglycolanhydride

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                    • #11
                      To clarify, for a 120V circuit, even though it is alternating current (AC) and the electrons are going back and forth, only one of the two circuit conductors is supplying the pressure to do so. It pushes at 120V and then pulls at 120V. The other, the neutral (grounded conductor), is just allowing the electrons to move, completing the circuit, but not supplying any pressure of its own.

                      On your typical household receptacle, you can shove a paperclip into the neutral hole, and you will be fine. But shove that paperclip into the hot hole, and you'll probably be shocked unless you've well-insulated yourself from anything that might be grounded.
                      Last edited by MAC702; 01-16-2020, 06:40 PM.

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                      • #12
                        Originally posted by Nipper View Post

                        So you're saying the neutral and ground are tied together in the main panel but not on the device being powered? In other words the neutral wire on the device will not have continuity with the ground lug or wire?
                        Yes, correct!

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                        • #13
                          OK then.

                          On this light socket I can see the three lugs would not have continuity.
                          But once its connected neutral and ground will have continuity on the device won't they?

                          So if they are both "drains" why don't some of the electricity go through the ground line?




                          On my main panel my neutrals and grounds are together and that bus is also grounded to earth. What makes the electricity go back down the neutral line and not to the ground or earth ground? It seems like there should be some diodes in the line so it just cant go everywhere.
                          Polyoxybenzylmethylenglycolanhydride

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                          • #14
                            Originally posted by Nipper View Post
                            OK then.

                            On this light socket I can see the three lugs would not have continuity.
                            But once its connected neutral and ground will have continuity on the device won't they?

                            So if they are both "drains" why don't some of the electricity go through the ground line?




                            On my main panel my neutrals and grounds are together and that bus is also grounded to earth. What makes the electricity go back down the neutral line and not to the ground or earth ground? It seems like there should be some diodes in the line so it just cant go everywhere.
                            Go back and read MAC's comment in #11...

                            Think of the neutral/ground (because of bonding) as a your "diode"...

                            Dale
                            Last edited by Dale M.; 01-17-2020, 10:38 AM.
                            "Fear The Government That Wants To Take Your Guns" - Thomas Jefferson..

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                            • #15
                              Originally posted by Nipper View Post
                              OK then.

                              On this light socket I can see the three lugs would not have continuity.
                              But once its connected neutral and ground will have continuity on the device won't they?

                              So if they are both "drains" why don't some of the electricity go through the ground line?




                              On my main panel my neutrals and grounds are together and that bus is also grounded to earth. What makes the electricity go back down the neutral line and not to the ground or earth ground? It seems like there should be some diodes in the line so it just cant go everywhere.
                              The electricity is going back to its source- earth is not the source.
                              Ed Conley
                              Screaming Broccoli, Inc
                              http://www.screamingbroccoli.net/
                              MM252
                              MM211
                              Miller Passport Plus, Spoolmate 100
                              TA185
                              SO 2020 Bender
                              Miller 125c Plasma
                              "Hold my beer while I try this!"

                              Comment

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