Need clarification on a 400 Amp Service grounding electrode conductor?

[jango]

I know that the required size of the grounding electrode for a typical 200 Amp service is a #4 solid copper. Now, we are planning on a 400 Amp service and I'm not sure what size PG&E will be running in the 3" PVC service lateral conduit but the length is approx. 300' so I'm assuming a pretty large set of service conductors. Now my question: I see in the NEC book under 250.66 that the required size of the grounding electrode conductor is based on the size of the largest ungrounded service entrance conductor. They already have a #4 solid copper which bonds to the concrete encased steel in the foundation which falls under 250.66(B) so am I fine to assume that based on this, regardless of the new service size being a 400 amp service and regardless of what size the service entrance conductors are, the grounding electrode conductor is code compliant being a size #4 solid copper?

 

[chris kennedy]

The service entrance conductors are after the service point. See Art. 100 definitions and don't worry about what POCO will use.

 

[kevin]

You seem to be assuming that the utility is installing the service entrance conductors, a highly unlikely event. See Art. 100 Definitions of Service Point and of Service Conductors. In any case, you are correct in your assumption that the minimum size of GEC, regardless of the size of the service, is 4AWG copper wire if connected to a concrete-encased electrode [250.66(B)].

 

[eprice]

Yes, based on 250.66(B), the GEC to a concrete-encased electrode is not required to be larger than #4 copper, regardless of the size of the service entrance conductors.

As a side note, I just wanted to point out, that using the definition of "Service-Entrance Conductors" in article 100, the service lateral conductors ran by the power company are not the service-entrance conductors referred to by table 250.66. In my experience "service-entrance conductors" are never ran by the power company. Around here most new residential services do not have service-entrance conductors since the service consists of a meter/main breaker combo fed by an under ground lateral.

 

[rcarroll]

Just curious, are there any other grounding electrodes? Like a copper water line. If so, a #4 copper won't work.

 

[jango]

Just curious, are there any other grounding electrodes? Like a copper water line. If so, a #4 copper won't work.

Actually yes. The GEC will run from the 400 amp panel, to the concrete encased rebar and then to the water pipe entrance for bonding the cold copper water pipe as well. Later they will then provide a bond between the hot-cold-and gas piping. Does this all sound correct and is the size of the GEC still code compliant to be #4 solid copper regardless of the service entrance conductors?

 

[augie47]

Directly to the CEE, a #4 is the largest required. To Rod or Plate a #6, but to other electrodes that might be present for a 400 amp, normally a 1/0.
If you GEC is "running to the CEE then on to water" it would need to be a 1/0 (or correct size per 250.66)
You can't have a weak link in the chain.

 

[DaveBowden]

Is the water service to the building metal?
If its not and all you have is interior copper water pipes then I would think the water piping isn't part of the grounding electrode system and all you're doing is bonding the water pipe. IMO that would require a # 3 copper conductor for a 400 amp main breaker.

 

[curt swartz]

Is the water service to the building metal?
If its not and all you have is interior copper water pipes then I would think the water piping isn't part of the grounding electrode system and all you're doing is bonding the water pipe. IMO that would require a # 3 copper conductor for a 400 amp main breaker.

Dave, 250.104(A)(1) requires the bonding jumper for metal piping to be sized per Table 250.66.

 

[augie47]

Dave, 250.104(A)(1) requires the bonding jumper for metal piping to be sized per Table 250.66.

it does ! (and I have never understood why ... are we afraid someone is going to add 10 ft of underground piping to it ? )

 

[DaveBowden]

All these years and I never noticed that one. Now I know why we've always sized it that way.
That's why I read this forum.
Thanks