... I know a GEC doesn't help with ground faults from hot to the safety ground path--so if it doesn't help in that case, how does it lower the voltage from lightning strikes, unintentional contact with high-voltage lines, grid surges from switching feeders, etc.?
250.4 General Requirements for Grounding and Bonding.
The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.
(A) Grounded Systems.
(1) Electrical System Grounding.
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.
So, 250.4 says it identifies what grounding and bonding are required to accomplish. And it is "prescriptive". It is going to tell us what to do and how to do it. No selection or choices on our part.
250.4.A.1 tells you what the grounding and bonding is going to do.
"will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation"
So, follow the rules and all good things will happen - or not.
1. "
and that will stabilize the voltage to earth during normal operation" So, is a lightning strike "normal operation. No. Wait a minute, it's normal operation, what is to stabilize.
2. So, is there any expectation that grounding/bonding
"will limit the voltage imposed by lightning"? No. Lightning strike hits close and raises the distribution MGN to 50KV. And the house? The house neutral/ground is tied right to the MGN. It goes right up with it.
3.
"unintentional contact with higher-voltage" Ok consider dropping a substation 69KV line across a 7200V feeder to suburban housing transformers. 69KV is 40KV to ground, the 7200V line jumps to 40KV, the service to the house jumps to 1300V and it is going to stay there until the substation protective relays open the feeder CBs - Or until the house CB opens or the meter disintegrates. And the ground rod is .................
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doing nothing until - Ahhh something flashed over.
4.
"line surges" So, what is that? It is not a switching transient, nor contact with a higher voltage line, nor lightning strike induce. "Surge" is not defined in the NEC. It is not defined in IEEE 100.
I have this picture in my mind of a Gary Larsen cartoon. House covered is arcing slime. Guy standing next to the house looking at the distribution line. There is a bulge traveling down the distribution line looking like a snake that swallowed a pig. "Oh, oh, here comes another surge."
Not to be confused with Art 280, 285 Surge Arrestors, Surge Protective Devices.
So 250.4, 250.4.A.1, No clue what they are talking about.
ActionDave in post 2 nailed it.
the worm (is being driven out of the ground by the "surges")