Bus-tie SSPCs for d.c. power distribution system

A direct current (DC) power distribution system (100) includes first and second electrical distribution and power management (EDPM) units (110A-B) comprising first and second DC power sources (101A-B), the first DC power source (101A) being connected to a first high voltage DC bus (104A) connected to a first bus-tie solid state power controller (SSPC) (103A), and the second DC power source (101B) being connected to a second high voltage DC bus (104B) connected to a second bus-tie SSPC (103B); and a bus-tie (109) connected between the first bus-tie SSPC (103A) and the second bus-tie SSPC (103B), wherein in the event a power source failure occurs in the first EDPM unit (110A), power flows from the second DC power (101B) source to the first HVDC bus (104A) via the second bus-tie SSPC (103B), the bus-tie (109), and the first bus-tie SSPC (103A).