What was found
CAPT UPPER LT PITOT HEAT CB AT P13-3 C1 INSIDE WIRE ARCED TO GROUND WHEN OPENING PANEL FOR INSPECTION. WIRES BURNT THRU AND SEPERATED AT P18-3 C1 CIRCUIT BREAKER DUE TO WIRE W18-217 BEING ROUTED INCORRECTLY AND CHAFING THRU PROTECTIVE COVER OVER TIME ON THE CIRCUIT BREAKER PANEL FRAME EDGE. WIRE WAS REPAIRED PER GNMM 2-0-21-001 AND AIRCRAFT WAS RETURNED TO SERVICE. DAMAGE WAS STRICTLY DUE TO IMPROPER ROUTING/CHAFE PROTECTION OF WIRE W18-217 TO ADJACENT STRUCTURE. 3 OTHER UAL 737 AIRCRAFT WERE INSPECTED AND FOUND TO HAVE WIRE W18-217 ROUTED CORRECTLY WITH ONE (N925UA) HAVING MINOR CHAFING REQUIRING ANTI-CHAFING SLEEVE INSTALLATION. NOTE THAT LOCATION IS AT P18 PANEL NOT P13 AS SHOWN IN 'DEFECT & CORRECTI