During locating geodetic stations using total station instrument, some lines between these pointes lying under existing high voltage networks of the Egyptian ministry of electricity (66 Kv) lead to an error in positioning there coordinates . It was necessary to study the effect of the High Voltage Power Lines on the accuracy of the above mentioned instruments measurements. It was also found necessary to establish the relationship between signal interference between EDM instruments , and the field caused by the electric power liens , and also the last distance of noticeable interaction between these electric lines add the signals of EDM to produce a maximum expected error of ( +_ 5 ) mm .