Relay inputs are verified over the specified ranges. Inputs include those for auxiliary voltage, VT, CT, frequency, optically isolated digital inputs and communication elements. Protection relay output contacts are type tested to make sure that they follow product. The functional tests consist of using the adequate inputs to the protection relay under test and measuring the performance to discover if it meets the specification. Even if the scheme has been thoroughly tested in the factory, wiring to the CTs and VTs on site may be incorrectly carried out, or the CTs/VTs may have been. In all cases, relay failures covered by self-diagnostics can alert operators through an alarm contact. This paper suggests a process for performing consistent and thorough commissioning tests through many sources: breaking out relay logic into schematic drawings; using SER, metering. The CMC 356 is the universal solution for testing all generations and types of protection relays. Its powerful six current sources (three-phase mode: up to 64 A / 860 VA per channel) with a great dynamic range, make the unit capable of testing even high-burden electromechanical relays with very. Although testing procedures have been well defined for single-function electromechanical (EM) protection devices, modern relay test procedures have been left to the utility to develop, creating possible shortcuts that may compromise the protection system operation.