What was found
DUB FLT 307 EN-ROUTE DUB TO PHL, DURING TAXI OUT, THE APU GENERATOR FAILED. THE FLIGHT RETURNED TO THE GATE WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND THE A-PHASE FEEDER WIRE BURNT FROM THE APU GENERATOR TO THE APU FIREWALL. THE APU GENERATOR WAS PLACED ON MEL. MAINTENANCE REPLACED THE BURNED APU GENERATOR FEEDER WIRE AND REMOVED THE MEL FOR THE APU GENERATOR. OPERATIONALLY CHECKS OK.