The innovative model HT Italia HT77N is a clamp meter for accurate measurements of very low AC current values. It is mainly employed in measuring leakage currents causing typical problem of RCDs accidental tripping on civil and industrial electrical installations. The built-in 100Hz low pass filter permits to cut off harmonic components. Some alarm thresholds can be selected on HT77N with acoustic indications depending on the measured current values. It is also provided with a sophisticated automatic backlight sensor to perform testing in dark environments. The meter complies with IEC/EN61010-1 safety standards under CAT III 300V.