A feed chain (16) has M feed outputs (31) for supplying a synchronous electric machine (14) with M phases. The feed chain comprises: a converter (22) for converting a direct input current into a polyphase alternating current; a storage bank; a detector (30) for detecting a short-circuit outside or inside the electric machine (14), a device (26) for insulating the electric machine (14) from overvoltages and/or overcurrents of the polyphase alternating current, and a controller (28) for controlling the converter (22) and the insulating device (26). The feed chain (16) includes short-circuiting device (27) capable of connecting the M power supply outputs (31) to each other, the controller (28) being capable of commanding the short-circuiting device (27) to perform that operation.