According to SOLAS, what means ,!main source of electrical ...

A source of electrical power, intended to supply the emergency switchboard in the event of failure of the supply from the main source of electrical power.

A condition under which any Services needed for normal operation and suitable conditions are not in working order.

A source intended to restore propulsion, the capacity shall be sufficient to restore propulsion to the ship in conjunction with other machinery, as appropriate, from a dead ship condition within 30 min after blackout.

A source intended to supply electrical power to the main switchboard for distribution to all Services necessary for maintaining the ship in normal operational and habitable condition.

A condition under which the main propulsion plant, boilers and auxiliaries are not in operation.