Abstract: The method is for testing an electrical component. The sender unit 12 may be applied to an electrical plug 24 that has a first line 28, a second line 32 and a ground line 36. It is determined which of the lines 28, 32, 36 that has a voltage potential relative to the surrounding. The phase configuration of the electrical plug 24 may be determined. The unit 14 is applied to a remote electrical unit and the sender sends a synchronization signal 41 to the receiver unit 14 that starts a counter providing a measurement of the time difference between corresponding phase positions of the alternating current of the plug 24 and that of the remote electrical unit. This time difference can then be converted to a phase difference value. The system may also be used to identify a specific fuse that is associated with the plug and for testing ground fault interrupting devices.