03420858H is the part number for the Littelfuse Varistor NTV7, a varistor from the Littelfuse TVRS series. The NTV7 is a non-linear voltage-dependent resistor which helps to protect sensitive electronic systems from overvoltage transients, such as those caused by lightning strikes or power surges. The NTV7 offers a fast response time of 15ns and an operating temperature range of -55°C to 125°C. The device has an AC voltage rating of 330V (60Hz) and a clamping voltage rating of 600V, making it suitable for many applications.