This standard specifies the general technical requirements for impedance measuring relays. These relays constitute a specific branch of measuring relays with multiple input excitation quantities as defined in IEC Publication 255-6 (Electrical relays Part 6: Measuring relays and protective devices). This standard specifies test methods and methods for expressing relay characteristics and performance. It includes those multi-input excitation quantity measuring relays with impedance as the characteristic quantity and whose operating characteristics are limited to the RX plane. This standard applies to self-set time limit or other timing relays. Those falling within the scope of IEC Publication 255-12 (Electrical relays Part 12: Direction relays and power relays with two input excitation quantities) are not included in this list. All tests in this standard are type tests. This standard applies only to new relays.