CTG is a family of "core balance transformers". These devices detect the difference in the current flow on the lines running through the coil. They work on either single phase or three-phase mains. When the vectorial sum of the current flowing to the load and the one flowing on the NEUTRAL cable (if present) is different from "0" (zero), a current on the CT secondary circuit is generated. The current difference is usually caused by a leak which may cause an hazard. The output signal can be used by a residual current monitoring device which will disconnect the monitored load or send an alarm signal. CTGs are used for detecting current leaks, potentially hazardous, on electric loads. Typically on electric motors, pumps or devices installed in metallic structures. They are approved to be used in conjunction with Carlo Gavazzi DEA71 and DEB71 earth leakage monitoring relays.