IEEE C37.103-2015 IEEE Guide for Differential and Polarizing Relay Circuit Testing.
Some verification procedures assume that a detailed check of the wiring for agreement with the elementary diagrams should be carried out prior to injection testing. Other verification procedures assume that any wiring errors will be disclosed by the actual injection tests. It is true that injection tests will disclose some wiring errors, but it should be realized that this procedure can damage the equipment because the wiring error may result in accidental injection of test quantities that exceed the rating of the inadvertently connected equipment. Also, errors may not be detected until incorrect operation occurs in service. Selector switches in current circuits, such as ammeter switches, should be checked for proper contact development and operation. When performing single-phase injection, three-phase and neutral current circuits should be monitored to verify the presence of current where it should be and the absence of current where it should not be. The three-line, elementary, or schematic diagrams should be used for the purpose of checking the connections.
Test jacks are used to allow current measurements to be taken without opening the circuits by inserting a test plug into a test jack. A test plug is a two-wire device connected to a current reading device. Inserting a test plug into a test jack places a current reading device in series with the current circuit. Before the test plug is inserted in the jack, extreme care should be taken to ascertain that a complete low-impedance circuit exists through the current reading device. This can readily be accomplished by using an ohmmeter. A low resistance from the polarity blade to non-polarity blade, with respect to the relay of the test plug, indicates a complete current path. A minimal amount of time is required to perform this test, and its usefulness in preventing the inadvertent opening of a CT secondary makes its frequent use worthwhile.
IEEE C37.103 pdf download.