Reply from: Sergio Panetta
The article "Equipotential Planes, A Figment of the Imagination" deals mainly with Utility Distribution systems and multiple grounded distribution systems. In multiple grounded distribution systems 40-60% of the neutral return current .. returns to the source substation through and/or over the earth.
Contrary to multiple grounded systems, single point grounded systems are grounded at one point and one point only. This point is usually the transformer or the service entrance switchgear.
Ground fault current will take all paths back to the source. The path with the least resistance will be along the bonding conductor.
Reply to Sergio Panetta Reply from: Mike Holt
The statement that "Grounding conductors do not
carry ground fault current. Figure 1 illustrates the two types of grounding."
Really relates to Figure 1. In this example, when there is a ground fault the 'grounding conductor" (called the grounding electrode conductor) is not called to carry any fault current. Fault current will be carried on the 'boding conductor.'
Reply to Mike Holt Reply from: Yakov Shmayevich
Existing lamppost has no grounding rod but has 4 anchor rods encased in cement. Adding a grounding rod is not practical in the City. If it was though doesn’t this just add a second potential?
Would isolation transformer help if neutral was not connected to pole in any way. 88% of the stray voltage poles are from failed or unbalanced neutrals. If not how is this application different from use in hospital or staging applications of isolation transformers?
The national electric code does not seem to address the issue of energized street light poles.(250.96) We are looking for advise from real world applications and operational realities not what a book says. The utility reverts to nesc and the workers revert to the nec. The reality is we have this problem.
Reply to Yakov Shmayevich Reply from: Mike Holt
You bring us a lot of issues and let try to address them:
1. The grounding of the metal pole to the earth is not needed and it service no purpose if it was.
2. There is no such thing as an isolation tranfrormer to prevent 'stray volage' or electric shock. If you mean an ungrounded system, then you still have the problem with electric shock, and the associated troubles with ungrounded systems.
3. The NEC is very clear on the proper grounding (bonding) of metal parts to ensure that they are not energized. See 250.4(B)(3) and (5).
4. The NEC is very clear on how to prevent stray voltage, see 250.6.
5. If the utility wires a metal pole, they follow the NESC and that standard allows the neutral to be bonded to the metal pole if the pole is grounded to the earth (this guys don't get it). This would never be permitted by the NEC.
I guess, my next quest is to shame the NESC into grounding (bondin) metal poles properly so that we don't have energized metal parts... long story.
Reply to Mike Holt | 
