This can't be answered without knowing the voltage, and ground is not the same as neutral, in AC circuits, which I'm assuming this is.
The neutral wire will be the same size as the service feeders. It will be a #6 copper conductor.
For a service conductor drawing 600 amps a #1 copper grounding conductor is needed.
For a standard 200 amp service 3/0 copper or 250 MCM aluminium.
Minimum # 10 gauge solid copper.
The size of wire you need is #8 bare.
A 200 amp service panel will require a # 4 bare copper ground wire.
Number 2 American Wire Gauge
On a 200 amp or any size service the ground wire is easily identified. Look in the distribution panel for the neutral bus bar. This is where the service neutral (white wire) is connected to the distribution panel. There you will see a bare copper wire connected to the same neutral bar. This is the ground wire that is connected to the ground rods out side of the house.
Yes, they are the same size wire.
You do not use a ground wire in the connection from the meter base to the distribution panel. A bonding wire may be required if the service is using PVC conduit.
10 guage
A 200 amp service panel will require a # 4 bare copper ground wire.
Service wire required is AWG # 3/0 copper.
AWG # 3/0 copper.
As a service entrance wire you need AWG # 3/0 gauge copper.
200 amp service in chicago uses 3 aught.
Number 2 American Wire Gauge
A 200 amp service panel with a 60 amp sub-panel.
Yes, there are ground wire gauges. The approiate size ground wire must be matched to the size service you are installing. For instance a 200 amp serivce must be grounded with a # 4 bare copper ground wire.
On a 200 amp or any size service the ground wire is easily identified. Look in the distribution panel for the neutral bus bar. This is where the service neutral (white wire) is connected to the distribution panel. There you will see a bare copper wire connected to the same neutral bar. This is the ground wire that is connected to the ground rods out side of the house.
NEC code requires #6 bare copper.
Your service provider will give you that information The size will depend on: A) how close to the transformer are you. B) copper or aluminum C) Yes, you have a 400amp service but what will your actual peak amp usage be. D) Underground or overhead.