CT (current transformer) secondary star point is often earthed for safety reasons. CTs are used to measure electrical current flowing through a circuit, and they work by inducing a current in the secondary winding that is proportional to the current in the primary winding. This secondary current is typically much smaller than the primary current, and is therefore easier to measure.
When the secondary winding is earthed, it provides a path for any fault current to flow to earth, rather than through the CT’s secondary circuitry. This can help protect the CT from damage in the event of a fault, and also prevent electrical shock to personnel who may come into contact with the CT or its wiring.\\\;\\In addition to safety considerations, earthing the CT secondary winding can also help to reduce noise and interference in the measurement circuitry. By providing a reference point for the secondary winding, it can help to eliminate any common-node noise that may be present in the system