Ground is sized based on the size of the feeder wire and not the amps of the service!
However, for a 600 amp service 1500MCM copper wire is one option (NEC 310.16) ;therefor, ground wire is 3/O copper (NEC 250.66)
or
another option is a two sets of 350 MCM copper wire then a #2 copper (since the biggest feeder wire is 350MCM).
Ground is sized based on the size of the feeder wire and not the amps of the service! However, for a 600 amp service 1500MCM copper wire is one option (NEC 310.16) ;therefor, ground wire is 3/O copper (NEC 250.66) or another option is a two sets of 350 MCM copper wire then a #2 copper (since the biggest feeder wire is 350MCM).
From the question it is hard to establish whether the service size is 350 amps or the service conductors are 350 MCM in parallel. If the service is 350 amps, the grounding conductor is #3 bare copper wire. Parallel 350 MCM conductors will allow for a 600 amp service. The grounding conductor for a 600 amp service is a #1 bare copper wire.
The wire size used in a service entrance distribution panel is governed by the size of the services over current device. The larger the service, the larger the fault current could be, the larger the ground wire to carry the fault current to ground. If the largest service conductor carries 100 amps use a #8, 200 amps - #6, 400 amps - #3, 600 amps - #1, 800 amps - 1/0 and over 800 amps - 2/0 for the ground wire. <<>> Golden Valley Electric Assoc. in Alaska requires #4AWG copper wire for a ground from the breaker box to earth ground rod. The same goes from the service entrance panel on the pole.
For Service Entrance Cable 600 kcmill (Thousands of circular mils).
For a 200 amp service with a 60 foot run, it is recommended to use 3/0 AWG copper wire or 250 kcmil aluminum wire to ensure proper voltage drop and capacity for the load. Be sure to consult with local codes and a licensed electrician for specific requirements and installation guidance.
Notes: 1. Where multiple sets of service-entrance conductors are used as permitted in Section 230-40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set. 2. 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. 1 This table also applies to the derived conductors of separately derived ac systems. 2 See installation restrictions in Section 250-64(a).
A 1600 amp service typically requires 500 kcmil copper wire or 750 kcmil aluminum wire. It's important to consult with a qualified electrician to determine the exact size and type of wire needed for your specific installation to ensure safety and compliance with local electrical codes.
This size service can be wired in a few combinations. Two parallel runs of 1250 MCM, three parallel runs of 600 MCM, four parallel runs of 350 MCM. Of the three choices the four runs of 350 MCM wires would be the easiest to handle if there are any bends in the service entrance conduit.
There is no one wire that is rated for 1800 amps. The service will have to be a quad parallel of the conductors. A 600 MCM conductor with an insulation factor of 90 degrees C is rated at 475 amps. This conductor paralleled into four equal lengths will give an ampacity of 1900 amps for each leg of the service.
A 350 MCM copper conductor with an insulation rating of 90 degree C is rated at 350 amps.
The wire size for 600 amps on a single wire 1250 MCM. A 1250 MCM copper conductor is rated for 645 amps with an insulation rating of 90 degrees C. This size of wire is too large to handle easily when it comes to the terminations. A service requiring 600 amps is usually paralleled or tripled which reduces the wire size which makes the wire much easier to handle. For a parallel service two 350 MCM cables are used and for a triple parallel run three 2/0 conductors are used. These conductors all have an insulation rating of 90 degrees C.
The size of wire for service entrance conductors for a 400 amp 3 phase service could be 500 MCM copper. This is very large size wire and difficult to bend and shape, to connect to terminals in the main disconnect and distribution panel. This problem is solved by using parallel conductors or on higher ampacities triple conductors. Using parallel conductors the wire size would be three ought (3/0) copper.