A300
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
General Maintenance Action; General Flight Cancelled / Delayed
Aircraft
During A300 preflight Aircraft X Captain touched base of rotating beacon switch on overhead panel (cleaning cockpit) and Captain received a sizable electric shock. (Painful; but no injury or burn) switch position was off.  Gingerly touched beacon switch a second time; could not duplicate; until I rubbed the base of switch; received a second jolt.  At that time I called Maintenance.  At first Mechanic could not duplicate; but eventually he got jolted.  At this juncture I was writing up [the] discrepancy and Mechanic opted to de-power aircraft which we did for him as he removed the aircraft exterior lighting panel on the overhead.  While he was inspecting the internals of the beacon switch my FO and I noted aircraft wire bundles that brought power from aircraft electrical system to cannon plugs for the overhead panel components had frayed wire insulation and exposed copper wiring.  Wires were particularly frayed on outside of bundles (perhaps rubbing internal frame) and around the zip tie wraps containing the bundles. While I was present the Mechanic removed nearby panels for SELCALL panel and the ignition/starter/wiper control panels and bare copper wire areas with eroded wire insulation was found again on multiple wire bundles. Afterward I recorded the additional wiring issues I witnessed under the two additional panels removed in a second further write up.  Again for clarification I would like to stress these were not wires on individual components; but wires from aircraft electrical system to the cannon plugs feeding the components.  At this point aircraft was removed from service and we swapped aircraft and flew our flight normally.  Obviously this is a potential concern.  My main concerns are as follows: 1. Determining if this a known issue and already being tracked?  2. Determining if this issue is specific to this aircraft or fleet wide issue?  3. Determining was this the cause of the shock or an independent event that uncovered a potential wiring issue?  4. Determining if suspicion that remaining unchecked overhead panel wire bundles contain frayed exposed wiring is correct.
A300 Captain reported being electrically shocked when cleaning the rotating beacon switch on the overhead panel. Maintenance removed the lighting panel on the overhead and it was noted wire bundles showed frayed insulation and exposed copper wiring.