Propulsion system for multi-rotor rotary wing aircraft, comprising: ▪ an electrical power source capable of outputting a power supply current, ▪ an electrical power supply bus connected to the electrical power supply source, and ▪ at least four motor units , each motor unit comprising a control circuit , an electric motor connected to the control circuit and a propeller mechanically connected to a rotor of the electric motor, the control circuit being capable of supplying power to the electric motor from the power supply current output by the electrical power supply source, the propulsion system being characterized in that it further comprises: ▪ an annular electrical network capable of connecting each motor unit control circuit to the electrical power supply bus, the annular electrical network comprising: - an electrical line , of which a first end and a second end are connected to the electrical power supply bus, the electrical line being interrupted at each motor unit and comprising a first connection point at its first end and a second connection point at its second end, and - for each motor unit , a first switch and a second switch , the first switch connecting the motor unit control circuit to the first connection point of the electrical line, the second switch connecting said control circuit to the second connection point of the electrical line. ▪ an electrical power source capable of outputting a power supply current, ▪ an electrical power supply bus connected to the electrical power supply source, and ▪ at least four motor units , each motor unit comprising a control circuit , an electric motor connected to the control circuit and a propeller mechanically connected to a rotor of the electric motor, the control circuit being capable of supplying power to the electric motor from the power supply current output by the electrical power supply source, the propulsion system being characterized in that it further comprises: ▪ an annular electrical network capable of connecting each motor unit control circuit to the electrical power supply bus, the annular electrical network comprising: - an electrical line , of which a first end and a second end are connected to the electrical power supply bus, the electrical line being interrupted at each motor unit and comprising a first connection point at its first end and a second connection point at its second end, and - for each motor unit , a first switch and a second switch , the first switch connecting the motor unit control circuit to the first connection point of the electrical line, the second switch connecting said control circuit to the second connection point of the electrical line. - an electrical line , of which a first end and a second end are connected to the electrical power supply bus, the electrical line being interrupted at each motor unit and comprising a first connection point at its first end and a second connection point at its second end, and - for each motor unit , a first switch and a second switch , the first switch connecting the motor unit control circuit to the first connection point of the electrical line, the second switch connecting said control circuit to the second connection point of the electrical line. <EOS>