GEC Size to Concrete-Encased Electrode?

[shortcircuit2]

I have a service with 3 separate service disconnect switches rated 200amp each with 4/0 copper service entrance conductors tapped from 500MCM copper main service entrance conductors in a trough ahead of the switches.

My only grounding electrode for the building is a concrete-encased electrode.

Using the method allowed in 250.64(D)(1)(3) for my taps to a grounding busbar, I select #4 copper for my taps based on the 4/0 copper feeding each switch.

What size common ground electrode conductor is needed to the concrete-encased electrode from the grounding busbar is required?

 

[petersonra]

I think if you look at the code the connection to the CEE itself is not required to be larger than #4 regardless of the service size.

 

[augie47]

I agree with Bob. 250.66(B) in the 08 NEC

 

[kwired]

If you run the 4 AWG from the CEE to the trough ahead of the disconnects, you bypass any confusion or misunderstandings of what sizes may be used if running to the disconnects, and is simpler and acceptable to do.

 

[suemarkp]

Do you have metal pipes to bond? If so, those will need a larger wire from your large neutral in the trough. It may also be permissible to run this larger wire from one of the panels as long as the neutral to that panel is sized to 250.66 based on the 500 KCMil Service conductors.

 

[infinity]

I think if you look at the code the connection to the CEE itself is not required to be larger than #4 regardless of the service size.

I agree. A #4 GEC is all that's required regardless of the SEC sizes.

 

[shortcircuit2]

In the graphic below, the bottom quote says to size the GEC based on the sum of the circular mil area of the largest ungrounded service entrance conductor...but it appears to me the GEC connection in the graphic is to a concrete-encased electrode.

 

[infinity]

In the graphic below, the bottom quote says to size the GEC based on the sum of the circular mil area of the largest ungrounded service entrance conductor...but it appears to me the GEC connection in the graphic is to a concrete-encased electrode.

That is correct. If the SEC's required a GEC smaller than #4 you would use 250.66 to size it. 250.66 also lists #6 and #8 as a GEC size.