Cessna 402/402C/B379 Businessliner/Utiliner
Flight Crew Air Transport Pilot (ATP)
Time Pressure; Confusion; Distraction; Troubleshooting
Aircraft Equipment Problem Less Severe
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Diverted
Aircraft
Cruise flight 70 NM from [destination]; a passenger alerted us that he saw smoke coming from the left circuit breaker panel. I looked down and confirmed that there was in fact smoke coming from the panel. Performed memory items and referenced QRH. [Advised] ATC. The isolation of the electrical systems stopped the smoke. We diverted to ZZZ (~40 NM) as it was closer than [destination] and would have emergency response crew. Landed at ZZZ and performed emergency ground evacuation per the QRH. Fire crews inspected the plane and were not able to find source of smoke but did detect a strong smell of a previous electrical fire. I suspect the source of the smoke was from the heater and or heater fan which was turned on 15 minutes prior; or it was possible it was the lightning strike detector. No circuit breakers or switch breakers were tripped. Aircraft was fresh out of phase; perhaps Functional Check Flights after phase could prevent this experience for passengers. These passengers were on the previous flight which had an air return for a rough running engine.
Cessna 402 Captain reported that a passenger noticed smoke coming from a circuit breaker panel. After confirming that an electrical problem did exist; the Captain elected to divert a suitable nearby airport.