The technology relates to detecting the wiring phase of an unknown phase voltage relative to a reference phase voltage in an electric power distribution system having a polyphase power line. In order to reliably detect the wiring phase at the remote location relative to a reference wiring phase even if the remote location is at a larger distance from the reference location, at least one relay location is arranged between the reference location and the remote location and connected to the wiring phase of the polyphase power line. A first phase relation is detected between the reference wiring phase voltage at the reference location and the wiring phase voltage at the relay location. A second phase relation is detected between the wiring phase voltage at the relay location and the wiring phase voltage at the remote location. The wiring phase of the remote location relative to the wiring phase at the reference location is detected based on the first phase relation and the second phase relation. The technology is advantageous in that a direct communication channel between the remote location and the reference location for detecting the phase relation is not required.