For service sizes of 100 amps and less a #8 bare copper conductor is required.
This answer is taken from the CEC. Table 17 states minimum size of grounding conductors. For a service conductor drawing 400 amps a #3 copper grounding conductor is needed. Also see rules 10-206, 10-700 and 10-812 if you have access to the code book.
The grounding conductor of a service distribution is sized by the ampacity of the service. By just stating the wire size, this does not give this information, as many variables enter into what wires are used depending on length, ambient temperature and insulation factor to name a few.
A 100 amp residential service requires a size #8 copper wire, it should be insulated in green.
hawt
3/0 awg wire
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.
This answer is taken from the CEC. Table 17 states minimum size of grounding conductors. For a service conductor drawing 400 amps a #3 copper grounding conductor is needed. Also see rules 10-206, 10-700 and 10-812 if you have access to the code book.
#2
Answer for USA, Canada and countries running a 60 Hertz supply service.CEC states that a #3 bare copper conductor is a common grounding conductor size for a 200 amp service panel and it is the minium size for service raceway and service equipment of 400 amps.
A conductor used for grounding of the main service should be a single wire. The code book has a table that states the size of ground wire for different service panel amperages.
The grounding conductor of a service distribution is sized by the ampacity of the service. By just stating the wire size, this does not give this information, as many variables enter into what wires are used depending on length, ambient temperature and insulation factor to name a few.
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.
A 100 amp residential service requires a size #8 copper wire, it should be insulated in green.
Generally a #6 copper conductor will do the job. The key to this grounding is that the ground conductor has to be taken back and connected to the service ground wire for optimal performance.
In Canada it is a #6 bare copper conductor that connects the grounding rod or plate to the neutral point in the distribution panel.
A #14 wire will do fine for grounding a 20 amp device. That is the size of the ground wire in a 2 conductor # 12 wire building cable.
hawt