RCD/RCCB is the commonly used ELCB type. An RCCB typically consists of a current transformer, which has multiple primary windings and one secondary winding. Neutral and line (or lines in multiple phase systems) wires act as the primary windings. A wire wound coil is the secondary winding. The current through the secondary winding is zero at the balanced condition. In the balanced condition, the flux due to the current through the phase wire will be neutralized by the current through the neutral wire, since the current, which flows from the phase will be returned to the neutral. When a fault occurs, a small current will flow to the ground also. This makes an imbalance between line and neutral current creating an unbalanced magnetic field. This induces a current through the secondary winding, which is connected to the sensing circuit. This will sense the leakage and send signal to tripping system.