This paper describes how the phase sequence and voltage level (132 kV, 275 kV or 400 kV) of single-circuit overhead conductors can be calculated from measurements made by passive, non-contact sensors situated on a moving platform at ground level.The investigation relies on sensing the electric field along the profile of the conductors through the use of passive sensors. The fabrication of the passive sensor is described together with an analysis of its performance. The variation of the vertical component of electric field strength along the lateral profile beneath single-circuit conductors has been studied using finite element modeling software, ANSYS. The results of this simulation have led to a proposed method of determining the magnitude and phase sequence information from overhead conductors via analysis of the induced voltages on the sensors.The paper concludes with an investigation made in a 400 kV substation in the UK. Analysis of the experimental results shows that the proposed technique can successfully evaluate the phase sequence, voltage level, the spacing between phases and the orientation of high-voltage overhead conductors.