Phoenix Fire Department Capt. Scott Walker tells The Associated Press about 35,000 gallons of mineral oil, enough to fill two swimming pools, is burning inside one of nine transformers on the ground and will likely burn for hours.
The smoke is going up and dissipating as fire crews use water and foam to snuff out the flames.
There are no evacuations and no health concerns with the nearest home about a mile away.
The fire started around 10 p.m. Monday and the cause is unknown.
Pinnacle Peak Road is closed between Tatum Boulevard and Scottsdale Road.