The CNV 508N4 series are special coupling/decoupling networks being used to perform "Electrical disturbance tests for measuring relays and protection equipment" in accordance to IEC 60255-26. A capacitance of 0.5uF is specified to couple the pulses on to the lines. Each line has a decoupling inductor of >1.5mH to protect the auxiliary equipment from being subjected to the test pulse. The disturbance signal used for this test is a damped oscillatory pulse with a frequency of 1MHz, generated by the EM TEST OCS 500N6 or OCS 500N6F generators.