Application Note Leakage current & clamp meters Leakage current is most generally any unwanted current in the circuit, element or installation. The reverse current in diodes, DC current through capacitor, or any current that flows to the device chassis or to the ground in the installations, can all be referred to as leakage current. It is a consequence of imperfect insulation and imperfections in electrical elements. It is usually very small but can accumulate to significant values – it the main limiting factor to the speed of silicone chips, and a reason for considerable power losses in large installations. In installations, the main cause is imperfect insulation. In AC conditions it starts exhibiting both capacitive and inductive character, and it conducts a small amount of current through both of them, while in DC the resistance just isn’t infinite. Longer wires have higher capacitance, and electronics devices use large capacitors in filters on input, adding to the effect. This current can be noticed as a difference between phase and neutral wires, or as a current in earth wire. Sometimes, particularly if the insulation is old or damaged, or if there is an earthing fault, it can accumulate charge on conductive surfaces on the chassis of a device and become dangerous to user. It can also accumulate to values high enough to trip a RCD. What do we do about it Leakage current, like any fault, needs to be quantified so that the source can be found. One of the ways to go about it is with a leakage clamp meter. Compared to other clamp meters, the leakage ones can sense currents down to about 0.1 mA. Make the measurement carefully, as it is at the lower edge of instrument’s measurement range. The clamps should close perfectly, the wire go between the arrows and lie as perpendicularly as possible to them. Measurements are made on phase and neutral wires lead

to system of interest or on the ground/PE wire. One should clamp it around both phase and neutral wires, or all the wires in three-phase system. The currents in them should have cancelled each other out, so anything that is left is a leakage current of the measured system. In case of ground wire measurement, it is the only wire to clamp. Any current in it likely comes from conductive parts of the chassis od a device. Clamping all three wires shows the current imbalance caused by unintentional path to the ground. One can calculate the insulation impedance from nominal voltage and measured leakage...