Why isn't ground fault protection required for panels under 1000 amps?

[JW9]

Why isn't ground fault protection required for panels under 1000 amps? Wouldn't a ground fault on a lower amp panel have the potential to trip a main breaker and take down a whole switchboard/switchgear/substation?

 

[ron]

I always guessed it was a line in the sand that had to be picked and a nice round number like 1000A seems nice and likely makes the requirement apply to larger/important buildings.
Same is for 25 ohms as being the threshold for needing a 2nd ground rod (if one exists), just a nice number

 

[jim dungar]

Why isn't ground fault protection required for panels under 1000 amps? Wouldn't a ground fault on a lower amp panel have the potential to trip a main breaker and take down a whole switchboard/switchgear/substation?

Adding ground fault to feeder breakers is a design consideration. Multiple levels of GF can result in a coordinated system which limits the area affected by a fault.

"We can afford an unexpected facility wide outage but we can't afford a coordinated system."

 

[jaggedben]

I always figured that it was because above a certain amperage you could have a really big, serious fault that still wasn't enough amps to trip the breaker at its rating. And otherwise it was a line in the sand like Ron said.

 

[electrofelon]

The NEC handbook says that the requirement was first "in the 1971 code because of the unusually high number of burndowns reported on those types of service.". So sounds like there was data on this, but I haven't dug into it.