Like any other device, current sensors and transformers must have at least one ground, namely in low-voltage circuits (below 1,000 volts). Although most systems are protected against sudden surges, it pays to add extra insurance to ensure the safety of the circuit, be it a solid-core, split-core, or Rogowski coil.
Grounding attaches a less-resistant conduit to the earth to provide as a return line for an excess charge, particularly one provided by lightning. Electricity follows the path of least resistance, so a ground connection can keep devices working and save lives. The earth is a poor conductor of electricity, after all, making it a suitable detour for excess voltage.
Grounding, in this case, often refers to secondary winding. As this winding is connected to the measuring apparatus, a surge in voltage along the conductor can result in fluctuations in the readings. In some cases, the apparatus itself may sustain damage from the surge, making any assessment next to impossible. It can also refer to the primary winding, the conductor itself.
Only one ground is necessary for the entire circuit. Too many ground connections may result in discrepancies in readings during testing. To prevent this, experts suggest installing the ground at the switchboard terminal instead of the CT.