Ground Ring

[kfenn22]

Does anyone understand the reasoning behind some engineers calling out the ground ring to use #4/0?

For example, If the Main Service is rated at 150A which the GEC is would be #6. But in the spec they call out #4/0 to be the ground ring conductor? Why not keep it #6 awg? I guess I don't understand the over kill of copper.
(This is an extreme example, but have seen other engineers do this.)

According to Article 250.52(4) the Conductor can not be smaller then #2 awg.

Am I missing something?
Thanks...

 

[charlie b]

I've spec'd that before. I think it is just to provide mechanical strength and durability, as opposed to any electrical consideration.

 

[bphgravity]

I have seen many examples of engineers/architects calling for way oversized GEC's and excessive grounding electrode specifications.

For example, I recently recieved a plan for a small assembly occupancy which called for 3 - 30 foot copper weld ground rods installed in a triangle formation not greater than 10 feet from each other and connected with a 3/0 GEC.

What is funny is that the engineer neglected to identify the concrete encased electrode and the building steel which will be present. The service is 400A.

How you can be so overkill on a waste of time ground rod design and miss essential code requirements is beyond me. Fortunately I had some other issues with the plans thus I was able to reject them and ask for a clarification on the Grounding System.

 

[dereckbc]

Ditto to Charlie, it is mechanical-connection-durability issue. More times than not the molds for thermal weld are available for 2/0 and 4/0

 

[tom baker]

My opinion is that the GEC connection to the ground rod is important at lightning frequencies and currents, an ohm or two in a poor connection is a substantial impedance to lightning.

Also, with lightning, the difference between a 4 AWG GEC and 4/0 GEC is negligible. Now if you use copper strap that will reduce the impedance considerably.

But I also agree its a durability issue. I use 2 AWG on my ground rods and antenna masts, as its cadwelded and the larger size will be better if hit with a shovel.

 

[iwire]

I think it is just to provide mechanical strength and durability, as opposed to any electrical consideration.

I have always assumed that was why the local power company specs 4/0 as a grounding ring around the transformer pads we make.

A 4/0 cad welded to a 3/4" x 10' rod regardless if it is electrically effective will last a very long time.