Available fault current approximation

[kwired]

keep in mind it takes a longer distance than you probably think to get under 10k where you have 65K upstream. For a 200A feeder its going to be around 150 feet. OP has an 800A which is 4 times the wire so it going to take a lot of length.

Yes, the larger the conductors the less that fault current will go down. A 60 or 100 amp feeder will drop much quicker.

Also an 800 amp device at the load end is typically going to be higher rated than a 200 amp device even if selecting lowest available rating, and has good chance of being series rated with whatever branch devices are used with it, though you can't always assume this either. Not too often do you have say 15 and 20 amp general use and lighting circuits in an 800 amp panelboard either though. Those are more common in 400 amp and less panelboards.

Also just because the OP has 85k rated gear at the start of this doesn't necessarily mean there is 85kA available at that point. Doesn't necessarily mean something over 65kA is available either.

There is lots of places with 100 and 200kA rated fused switch for mains yet not that much current is available.

 

[Dsg319]

Bussman has an app a child can use. Hence why I have it