How do I size a bare ground conductor, used only for fault current, with respect to temperature?

[brycenesbitt]

Hmm.
I'm looking at wire size charts, and need to size a bare ground wire, to fault a 400A breaker.
What's unclear is what temperature rating to use for a bare conductor, especially if it's in conduit that makes the same connection.
What if it's in the same conduit as 70C wire and could melt that wire?

How should I think about sizing the ground?
Can I put 2 AWG on it, and call it a day?

The upstream equipment can fault more than 400A, so that current has to be able to carry all the way back to the main
breaker to get it to trip.

Ref: Current carrying capacity is defined as the amperage a conductor can carry before melting either the conductor or the insulation. Heat, caused by an electrical current flowing through the conductor, will determine the amount of current a wire will handle. Theoretically, the amount of current that can be passed through a single bare copper wire can be increased until the heat generated reaches the melting temperature of the copper

http://www.ee.nmt.edu/~wedeward/EE382/SP02/current_capacity.pdf

 

[infinity]

You look at Table 250.122 and chose the minimum conductor size based on the OCPD ahead of it. Doesn't matter if it's insulated or bare the size is the same.

 

[brycenesbitt]

You look at Table 250.122 and chose the minimum conductor size based on the OCPD ahead of it. Doesn't matter if it's insulated or bare the size is the same.

Does it matter if the grounding conductor is in the same raceway as wire with a lower temperature insulation value?
(e.g. potentially the ground gets hot, melts the other wire in the same raceway. Of course the bare ground will be fine all allong).

 

[infinity]

Does it matter if the grounding conductor is in the same raceway as wire with a lower temperature insulation value?
(e.g. potentially the ground gets hot, melts the other wire in the same raceway. Of course the bare ground will be fine all allong).

The EGC won't get hot. It is not under normal conditions a current carrying conductor therefore it generates no heat. During a fault the OCPD would quickly open and keep the EGC from heating or melting the adjacent conductors.

 

[brycenesbitt]

The EGC won't get hot. It is not under normal conditions a current carrying conductor therefore it generates no heat. During a fault the OCPD would quickly open and keep the EGC from heating or melting the adjacent conductors.

Yes, except in a frog boiling fault, at 399A for hours.
In a proper fault of course a much smaller wire would do, as long as it can pull enough current.