The purpose of this unit is to continue the development begun in Relays, Part 1 by introducing differential and pilot relays and discussing routine relay maintenance. The relays examined are differential relays and pilot relays used for differential comparison, phase comparison, and transfer tripping. The unit demonstrates how to inspect and maintain relays and how to put them in and out of service. At the conclusion of this unit, trainees should be able to explain how differential and pilot relays work and give examples of situations where they are used. They should also be able to describe how to approach routine inspection and maintenance and how to put a relay in or out of service.