Fluke - Basic concepts related to measuring leakage currents

In any electrical installation, current flows through the protective earthing conductor to reach the ground. This is generally referred to as leakage current. Most often, the leakage current passes through the insulation surrounding the conductors and through filters that protect electronic equipment in a residence or office.
What is the issue?
On circuits protected by residual-current devices (RCDs), the leakage current can cause unnecessary and intermittent tripping. In some extreme cases, it can subject certain exposed conductive parts to a voltage increase.