It is used for effective protection for circuits highly sensitive to "high frequency" interference. It is to be used only in cases where the voltage is virtually sinusoidal. i.e. less than 5 % total harmonic distortion.
Voltage limited to 3 Uc max. and oscillating frequency limited to 400 Hz max. Slight increase in drop-out time (1.2 to 2 times the normal time).

Released for: Schneider Electric India