In a “ladder” diagram, the two poles of the power source are drawn as vertical rails of a ladder, with horizontal “rungs” showing the switch contacts, relay contacts, relay coils, and final control elements (lamps, solenoid coils, motors) drawn in between the power. In a “ladder” diagram, the two poles of the power source are drawn as vertical rails of a ladder, with horizontal “rungs” showing the switch contacts, relay contacts, relay coils, and final control elements (lamps, solenoid coils, motors) drawn in between the power. 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. Also principles of various protective relays and schemes including special protection. Good and reliable selectivity of the protection is essential in order to limit the supply interruption to the smallest area possible and to give a clear indication of the faulted part of the network. This makes it possi-ble to direct the corrective action to the faulty part of the network and the. Relay ladder circuits are the precursor to PLC ladder logic. The selection and applications of. ve reliable and properly coordinated relay settings. First, each utility must develop a solid protection philosophy that establishes the guideline for setting the functionality of protective relays.
