Neutral and Ground in Main

Although I DO understand the concept of the neutral and ground busses being bonded in the MAIN panel only, this leads me to something I wonder about. Okay, so if a hot conductor were to come into a grounded fixture box or switch, the current would take the path of least resistance, which of course is the ground wire. This is said to happen because this wire has the least resistance, compared to a human contacting the fixture.
If both the neutral and ground return back to the panel, why then does the grounded fixture box carry the current back to the panel instead of the neutral continuing to do so? Also, since AC is current which is periodically changing in direction of flow, how does the ground bus bar remain with no current if it’s bonded to the neutral?
It would seem to reason that if they’re connected, they are the same thing essentially.

Only carries fault currents.

Think of a old metal drill the neutral white goes to the motor. The black hot goes to the switch then to the other side of the motor. The ground goes to the metal case that is isolated from the motor. If hot shorts to case ground you are less likley to get shocked as the current will flow to ground.

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Grounding is for safety.

Good questions. :sunglasses:

  1. Try to forget the term “path of least resistance”, current will follow all parallel paths regardless of their resistances making the concept of path of least resistance confusing. The purpose of the EGC (ground wire is too ambiguous) is to provide an effective ground fault path to quickly open the OCPD, this is from the NEC:

250.4(A)(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

  1. Because the box is not connected to the neutral in the box, the box is only connected to the EGC. The neutral would need to be in parallel with the EGC in order for it to carry current during the fault condition. To be in parallel with the EGC the neutral and the EGC would need to be connected together at both ends. So when an ungrounded conductor faults to the metal box only the EGC carries the fault current.

  2. Similar reason to #2 the neutral is not connected to the EGC anywhere but at the service disconnect, and during a ground fault the EGC only carries current briefly, just until the OCPD opens. The fact that it’s AC and cycles 60 times per second is not relevant.

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Those responses were apt and helpful guys! Thank you!

Robert gives excellent electrical responses! :smile: