Thank you for your welcome to the board and for your reply. On answer #2, I understand article 250.92 to require all service equipment to be bonded together. I do not se mention of the neutral in this area. I thought that the neutral could only be bonded to ground at one point to prevent ground loops?
On my question #6, regarding 6 - 3/0 cu conductors with 2 - 3/0 neutrals in a 3" GRC service mast for a 400-amp panel with 75º rated panel. The conductors are THHN. The service is 208Y/120 volts. It seems that if you count the neutrals then the wire size must be increased. What would determine if the neutrals are current carrying? I realize that if the service has a balanced load there will be no load on the neutral. Is there an article that addresses when a neutral is and isn't considered current carrying?
I suspect you are thinking about the location of the Grounding Electrode Conductor connection to the Grounded Conductor (Neutral) of the service entrance conductors. That connection may be made at any point between were the service entry neutral attaches to the utilities conductors and the buss bars in the service equipment enclosure.
250.24 Grounding Service-Supplied Alternating-Current Systems.
(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.
As for how to bond the service raceway and meter sockets that is covered by 250.92. I cannot find a definition for the term threaded bosses but I bet it covers hubs. If hubs are not covered then I would think that bonding that occurs in the meter base would be enough. If not I guess you could use an over length screw on one corner of the hub and attach a lug on that screw inside the can.
(A) Bonding of Services. The non?current-carrying metal parts of equipment indicated in 250.92(A)(1), (2), and (3) shall be effectively bonded together.
(1) The service raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath except as permitted in 250.84.
(B) Method of Bonding at the Service. Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
(2) Connections utilizing threaded couplings or threaded bosses on enclosures where made up wrenchtight
(3) Threadless couplings and connectors where made up tight for metal raceways and metal-clad cables
(4) Other approved devices, such as bonding-type locknuts and bushings