For US-N5/8SS(TE) and US-N70/80NS(TE), the rated impulse withstandvoltage is 4kV. For US-N20 to 50(TE) and US-NH70/NH80NS(TE), the ratedimpulse withstand voltage is 6kV. These meet the required impulsecharacteristic for power distribution equipment specified in IEC standard.