A supply system (2) for supplying energy in an aircraft comprises at least one electrical line (8) connectable to a current source (4), an electrically conductive shield (18), and a detection unit (20) having at least two electrical inputs. The at least one electrical line (8) comprises at least one core (6) connectable to a pole (14, 16) of the current source (4), wherein the shield (18) surrounds the at least one core (6) under a distance and creates an intermediate space between the at least one core (6) and the shield (18). At least one port of the detection unit (20) is connected to the at least one core (6) and wherein at least another port of the detection unit (20) is connected to at least one of the shield (18) and the at least one first core (6). The detection unit (20) is adapted for detecting a differential current over the at least one core (6) or an absolute current between the shield (18) and a ground potential. The detection unit (20) is further adapted for generating a warning signal if a predetermined threshold value for the detected current value is exceeded. Thereby an improved level of safety is reached in the electrical supply of an aircraft, especially in the vicinity of fluid lines transferring flammable or oxidizing fluids.