Don
It is the relative relationship between the resistance's of the paths that determine the current flow. The secondary path could easily have 10 to 20 times more resistance then the main path. A #12 has 10 times the resistance of a #4 and 20 times the resistance of a 1/0. If the path has 10 times the resistance, then only 1/10 of the total current will flow in that path.
I agree with this, but haven't you forgotten to take the length of the conductors into account? If the branch circuit has the same length as the feeder, there is probably no problem.
What about the feeder equipment grounding conductor back to the power source? If this is at a panel where there is a main bonding jumper, there is no current flow on the branch circuit grounding conductor with a grounded to grounding short at the receptacle, other then the division of the grounded conductor current for the receptacle load itself.
I take "main bonding jumper" to mean a connection between ground and neutral? If so, I fully agree with the above.
If there is a feeder equipment grounding conductor, then you have to add in that resistance. If we assume that the feeder equipment grounding conductor is the same size as the circuit conducotrs, which is not normal, then the relative realation ship is 5.4. This number will be even higher when the equipment grounding conductor is smaller than the circuit conductors.
You've got a point in that the grounding wire is normally smaller than the other conductors for large cables. However, in the case of 3-phase systems the neutral conductor is often downsized too. Therefore I'm not sure the downsizing of the grounding wire will have a significant impact.
What puzzles me is where you got the figure 5.4 from?
