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