This video illustrates how to meter the alternative voltage source (the Z source, in this case) on the SEL-451, SEL-411L, and SEL-421 relays. By default, only one terminal voltage can be metered via the MET command in the terminal on these three relays. This video shows how to perform freeform logic to meter the additional source on the front screen of the relay. View in fullscreen mode for the best image quality.