250.66 Totally Mystifies Me

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Skyline Electric

Skyline Electric

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Why do different sized services require different sized GECs?

What does a GEC really do and does it have ANYTHING to do with the size of the service conductors? It's my understanding that the GEC primarily provides a ground path for lightning and maybe "stabilizes" voltage, it connects to the grounding electrode which is a very high impedance ground. The GEC has nothing whatsoever to do with the operation of overcurrent devices.

Electricity wants to go back to it's source, not into the earth.

So, why the different sizes? What real science is behind this? 2/0 service conductors require a #4 GEC but what terrible health hazard would result if a #6 GEC were used instead?

I think this code section is ridiculous. I'll continue to abide by it but I think that these wire sizes were arrived at during a drunken bull session.
 
The GEC to just a ground rod does not have to be larger then 6 AWG CU.

The GEC to just a concrete encased grounding electrode does not have to be larger then 4 AWG CU.

However the GEC to a water pipe has to be sized based on the size of the service conductors because if the metal water service is common with other services the GEC might have to carry the entire fault current the power company transformer can provide.
 
iwire said:
However the GEC to a water pipe has to be sized based on the size of the service conductors because if the metal water service is common with other services the GEC might have to carry the entire fault current the power company transformer can provide.
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OK, maybe I can understand this, if my neighbor suffers a ground fault and our water systems are electrically common, the fault current could travel from his house to mine via the underground water pipes and then travel up my GEC and onward to the neutral of the service drop?

I hadn't considered this but it does seem possible. Wow, I've always viewed electrical systems as being independent and unrelated to other electrical systems, but this is very interesting, thanks.
 
Skyline Electric said:
Why do different sized services require different sized GECs?
Click to expand...

Consider that different types of electrodes have differing degrees of effectiveness.

Consider overvoltages and lighting strikes.

Consider that our understanding of this dictates the size of the electrode required to a ground rod, a rebar electrode, or building steel....

Whatever impact the size of the grounding electode conductor may have on the equipment during these conditions, it serves no purpose to provide a conductor larger than required for the given effectiveness of a particular electrode.

Crazy, but true.
 
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