This part of IEC 60255 specifies common rules and requirements applicable to measuring relays and protection equipment including any combination of devices to form schemes for power system protection such as control, monitoring and process interface equipment in order to obtain uniformity of requirements and tests.

All measuring relays and protection equipment used for protection within the power system environment are covered by this standard. Other standards in this series may define their own requirements which in such cases shall take precedence.

For special applications (marine, aerospace, explosive atmospheres, computers, etc.), the general requirements within this standard may need to be enhanced by additional special requirements.

The requirements are applicable only to relays in new condition. All tests in this standard are type tests, unless otherwise declared.