The HE20LC is a three terminal device, two of which are connected across the signal inputs of the detector for differential mode protection and the third terminal is grounded to protect against common mode damage.
Differential mode surges (induced voltage across the loop detector input terminals) are clamped by a semiconductor array instantly. The array is designed to appear as very low capacitance to the loop detector.
Common mode surges (induced voltages between the loop leads and ground) are handled by a rugged three element gas discharge tube which has a breakdown threshold of 90 volts DC. Thereafter the protector clamps the two loop leads to 28 volts with respect to ground. This design eliminates any ground noise from entering the loop detector and being amplified. The HE20LC is intended for all current detector models on the market today.
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