Methods and systems are described for communicating with downhole locations and transmitting power to downhole locations. Use is made of a cable passing someway down into the well. This cable may be connected to a downhole sensor and may be used primarily for communicating with that sensor, but also used in the current techniques described herein. Electrical connection is achieved between the cable and the metallic structure of the well to allow signals to be transferred between the communications tool and the surface via the cable.