This part of the Chinese relay series deals with the insulation coordination of protection and measuring relays and with the dielectric tests that verify it, and it is applied in China alongside the relay product standards that carry the disturbance requirements. The subject is of particular consequence for these devices because they are connected simultaneously to the high voltage system through their measuring inputs and to the low voltage auxiliary and communication circuits, so the insulation between circuits and between each circuit and earth is what keeps the equipment safe for the technician working on it. Chinese type testing places the insulation tests early in the programme, since a failure there makes the remaining tests pointless, and the report must record the clearances and creepage distances actually measured on the specimen together with the dielectric and impulse results. The standard is cited in the specifications of the network operators and of the major domestic relay manufacturers.