90.2(B)(2) If not here then where?

90.2 Scope.

(B) Not Covered. This Code does not cover the following:

(2) Installations underground in mines and self-propelled
mobile surface mining machinery and its attendant electrical
trailing cable

I work at an open pit copper mine, & we have self propelled 7200 VAC shovels.

My questions are:

1) Why doesn't the NEC cover the electrical in underground mines, or the self propelled mining equipment?

2) Does anyone know where I can find a Code/Regulation covering the electrical on mobile mining equipment? MSHA's Articles on electrical aren't very in depth....