System (Sys) for supplying decentralized functional units with electric power, arranged in an industrial facility, wherein: a. a subordinate control system is provided that exchanges information by means of a data telegram via a data bus (CB, NB1, NB2) with the decentralized functional units, b. network node units sequentially arranged between two feeding points (PS1, PS2) of an annularly structured energy bus, providing the decentralized functional units with access to the energy bus and optionally also to the data bus (CB, NB1, NB2), c. the network node units have a controllable switch module, comprising a first switch and a second switch, wherein an access to each of the two feeding points (PS1, PS2) is switchable by means of the two switches (S1, S2), d. the first switch and/or the second switch is optionally openable and a voltage is measurable declining at the inlet of the network node unit; and e. an evaluation module (CPU, SL) is provided, evaluating the measured voltage within one network node unit and/or among adjacent network node units upon an interruption of the energy bus and/or a defective switch module characterized in that an observation cycle is provided for gradually and/or simultaneously opening both switches for each network node unit by way of a gradual execution of the network node units, beginning at one of the two feeding points (PS1, PS2) or beginning at the network node unit, situated at the center of gravity for the voltage of the energy bus, and then in a both-sided expansion to the feeding points (PS1, PS2). a. a subordinate control system is provided that exchanges information by means of a data telegram via a data bus (CB, NB1, NB2) with the decentralized functional units, b. network node units sequentially arranged between two feeding points (PS1, PS2) of an annularly structured energy bus, providing the decentralized functional units with access to the energy bus and optionally also to the data bus (CB, NB1, NB2), c. the network node units have a controllable switch module, comprising a first switch and a second switch, wherein an access to each of the two feeding points (PS1, PS2) is switchable by means of the two switches (S1, S2), d. the first switch and/or the second switch is optionally openable and a voltage is measurable declining at the inlet of the network node unit; and e. an evaluation module (CPU, SL) is provided, evaluating the measured voltage within one network node unit and/or among adjacent network node units upon an interruption of the energy bus and/or a defective switch module characterized in that an observation cycle is provided for gradually and/or simultaneously opening both switches for each network node unit by way of a gradual execution of the network node units, beginning at one of the two feeding points (PS1, PS2) or beginning at the network node unit, situated at the center of gravity for the voltage of the energy bus, and then in a both-sided expansion to the feeding points (PS1, PS2). characterized in that an observation cycle is provided for gradually and/or simultaneously opening both switches for each network node unit by way of a gradual execution of the network node units, beginning at one of the two feeding points (PS1, PS2) or beginning at the network node unit, situated at the center of gravity for the voltage of the energy bus, and then in a both-sided expansion to the feeding points (PS1, PS2).