varying magnetic field formed by the current through the line 14 and hence the alternating current through the line suitable conductors 52 and 54 bring the current in the sensor 48 out of the coupling device 12 two conductors 58 and 56 carry the voltage between the shielding electrode 28 and the ground electrode 38 out of the housing 10 of the electrical coupling device 12 fig3 illustrates a system embodying the invention and including the electrical coupling device 12 here the conductors 52 and 54 bring the current in the sensor 48 to a local transmitter 56 the two conductors 58 and 60 connect the shielding electrode 28 and the ground electrode 38 across a capacitive voltage divider composed of a 40 pf picofarad capacitor 62 and a 4 000 pf capacitor 64 within the local transmitter 56 an analog to digital converter 102 converts the current sensed by the sensor 48 to digital form and passes it to a time division multiplexer tdm 104 similarly an analog to digital converter 106 converts the voltage appearing across the capacitor 64 to digital form and applies the resulting pulses to the time division multiplexer 104 the latter time division multiplexes the pulse representing.