It is presented a system for supplying electric power from a main power grid to a plurality of ships moored at a respective berth of a quay. The system comprises a connection point for connecting to the grid supplying electrical power at a first frequency, a frequency converter arrangement for converting electric power from the grid at the first frequency to electric power at a second frequency, a first connector, arranged to provide power from the grid at the first frequency, a second connector, arranged to provide power at the second frequency from the frequency converter arrangement, a plurality of switches, each switch being configured to supply of power from either of the two connector to a respective berth, the system further comprising a plurality of ship connection arrangements connected to a respective switch, each ship connection arrangement being adapted for connection to an electric system of a ship. A corresponding arrangement and method are also presented.