This handbook covers the code of practice in protection circuitry including standard lead and device numbers, mode of connections at terminal strips, colour codes in multicore cables, dos and donts in execution. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. Consideration is given to availability and location of breakers, current sensing devices, and disconnect switches, as well as bus-switching scenarios, and their impact on the selection and application of bus protection. Also principles of various protective relays and schemes including special protection. Recognized under 2(f) and 12 (B) of UGC ACT 1956 (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – 'A' Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Kompally), Secunderabad – 500100, Telangana State, India To introduce all kinds of circuit. Protection relays play a critical role in ensuring the safe and reliable operation of electrical power systems. Protection relays are designed to detect abnormal conditions, such as short circuits or overloads, and quickly isolate and protect the affected equipment. To ensure consistent performance.