110 (4), ER (Electricity Regulations) 1994; any protective relay and device of an installation will need to be checked, tested and calibrated by a competent person at least once every two years, or at any time as directed by the Energy Commission. Calibration of protection relays is critical to the reliability and safety of electrical power systems. This guide is designed to inform engineers, power system operators, and technical enthusiasts about the calibration process, its importance for different relay types, and best practices based on. According to Reg. While this is bad, It's not a. The protection circuits, CTs, VTs are also checked. Maintenance testing is done in field periodically. These are generally performed in laboratory. Power Line Carrier (PLC) Leased Line Microwave Fiber. The law requires that these relays are tested and calibrated once in 2 years.