HE20LC (Surge Protector)

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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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Peak Surge Current
Differential Mode 400A (8 x 20us)
Common Mode 5000A (8 x 20us)
Est. Occurrences 500 @ 100A (8 x 20us)
Response Time 5nS (Diff. Mode)
Input Capacitance (Typical)
Differential Mode <4pF
Common Mode <4pF
Temperature -40 to 85°C
Weight 2.5 oz.
Mounting #10-32 x 3/8 stud
Discharge Voltage:
@100A...45 Volts Differential Mode 28 Volts Common Mode
Holdover Voltage 72 VDC
Gap Breakdown Volts 90VDC @ 10KV/us


One HE20LC is used for each loop detector to be protected. HE20LCs are installed as close as practical to the point where the loop detector wires enter the controller cabinet. Connect one of the flexible leads to each end of the loop. The common connection (stud) must be connected to earth ground.

Best performance of this protector is obtained by: 1) Shortening the flexible leads as much as possible.

2) Providing the lowest possible impedance to ground.


  • Effective Surge Protection for 120 VAC Interconnect Signal Lines
  • Differential and Common Mode Protection
  • Years of Dependable Service
  • Automatic Recovery
  • Flame Retardant Epoxy Encapsulated
  • Easy Installation
  • Proven Field Performance Tested