DCM305E Earth Leakage Clamp Meter
Since there is no such thing as perfect insulation, if any conductor is raised to a potential above that of earth some current is bound to flow to earth from that conductor. The amount of current that flows is dependent on:
- Voltage on the conductor
- The capacitive reactance between the conductor and earth
- Resistance between conductor and earth
Currents that flow to earth are called leakage currents and are usually very small values, typically < 1 mA. However the amount of current that is required to cause distress or harm to a human being or animal is also small, these currents must be limited by circuit design to safe values.
If this is not possible, then a 30 mA RCD (residual current device) or 30 mA RCBO (residual current device with overload protection) should be fitted for personal protection.