A FIRE OCCURRED IN THE 480 VOLT ELECTRICAL SWITCH GEAR SERVICING THE NORTH 1/2 OF THE PLANT. CHICAGO CITY FIRE DEPT AND COMMONWEALTH EDISON (ELECTRICAL PROVIDER) RESPONDED. THE FIREFIGHTING R ESPONSE WAS DELAYED UNTIL THE SWITCHBOARD WAS DE-ENERGIZED. DAMAGE WAS LIMITED TO THE SWITCHGEAR PROPER. NO STRUCTURE DAMAGE TO FACILITY. ALL PLANT ELECTRICAL EQUIPMENT IS PCB FREE. NONE PRESE