This part of IEC 60255 gives general requirements for the insulation coordination of measuring relays and protection equipment. In particular, this standard, specifies the following: - definition of terms, - guidance for the selection of clearances and creepage distances and other aspects related to the insulation of measuring relays and protection equipment, - requirements for voltage tests and insulation resistance measurement. This standard is applicable to the installation and use at altitudes up to 2000 m of equipment having a rated a.c. voltage up to 1000 V with a rated frequency up to 65 Hz, or a d.c. voltage up to 1500 V. This standard also applies to associated auxiliary devices such as shunts, series resistors, transformers, etc. used and tested together with measuring relays and protection equipment as mentioned above, except where the devices are covered by other IEC publications, for example communication interfaces.