This is a 400 amp combination service entrance device, Square D CU12L400B to be exact. The size of the grounding electrode is determined by the size of the service entrance conductors. In this case you don't actually have any service entrance conductors but do have service lateral conductors. If the service lateral conductors are going to be installed by the EC the grounding electrode conductor should be based on the size of these conductors. If the service lateral conductors are going to be installed by the POCO I feel the grounding electrode conductor should sized as if they used 400 amp conductors. If this is a residential service it would require 400MCM CU or 600MCM Al service conductors so the grounding electrode conductor should be 1/0 CU.
Re: GEC sizing#86265 09/27/0303:02 AM09/27/0303:02 AM
Thanks for your replies. The reason I poseted this is to pose a question...Is this the installation that added footnote 2 to table 250.66? Bear in mind the definition of service entrance conductors. In this application there are either no service entrance conductors or they are the bus bars that come off of the load side of the meter.
I am of the opinion that that the bus bars are the service entrance conductors and therefore a 1/0 GEC is required. I don't think you are ever permitted to use the service lateral conductors to size with.
Ryan Jackson, Salt Lake City
Re: GEC sizing#86267 09/27/0311:43 AM09/27/0311:43 AM
Given that this is a service with four disconnects. . .I don't think the size is tied to the maximum possible service size (limited by the equipment), but rather by the calculated service size, determined by the occupancy's load where this is installed, plus a margin for growth that is the calculator's option. . .not requirement.
That is: What does the installers service calculation say the service is? The service conductor size used to determine the GEC size would be based on that "equivalent" conductor.
I am of the opinion that that the bus bars are the service entrance conductors
If we're taking a poll I would tend to agree with this (assuming it's an UG Service) because of the definition of Service Entrance Conductors in Art. 100.
In other situations the GEC is sized according to the Service Entrance Conductors and not the load. It wouldn't seem consistant to start looking at the load now.
Say this house has all Gas appliances and therefore a low calculated load. It's 200A OH service requires a #4 GEC. I change it to a UG service and with no change in loads it wouldn't make sense to me that I can now use a much smaller GEC.
Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.
230.90(A) Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.
It seems clear to me that for services it is all about the load and in the absence of service conductors the GEC is based on the calculated load not the potential load.
[This message has been edited by iwire (edited 09-27-2003).]
Bob Badger Construction & Maintenance Electrician Massachusetts