As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED "SMELL OF BURNING PLASTIC IN CABIN" AND RETURNED TO BASE. MECHANIC FOUND FAULTY GFCI OUTLET (LH MED WALL) READING ABNORMAL VOLTAGE BETWEEN UPPER AND LOWER RECEPTACLE SUSPECTING SHORT IN GFCI ITSELF. REMOVED AND REPLACED IAW REF. SUBSEQUENT OPERATIONAL CHECK WAS COMPLETED SATISFACTORY.