HDR - Harmonic Drainage Reactor

  • HDR - Harmonic Drainage Reactor
  • HDR - Harmonic Drainage Reactor

Noise Mitigation Equipment

SNC A/C Induced Noise Solutions

Harmonic Drainage Reactor - HDR

Drain Interfering AC Voltages and Currents to Ground with an HDR

The SNC HDR is designed to provide a path-to-ground for induced harmonic interfering AC voltages and currents. If you’re seeing symptoms such as noisy subscriber lines, impulse noise, or “hot” or “shocking to the touch” line facilities, or if your Noise Choke or Induction Neutralizing Transformer (INT) does not properly excite at harmonic frequencies, you may need an HDR.


Download and View HDR Application Notes T0046.


Harmonic Drainage Reactor – P15168 Protected Harmonic Drainage Reactor – P15173


  • Subscriber/Open Wire Lines
  • Telemetering/Radio Pickups
  • Data Modems/Alarm Circuits
  • Induced AC Voltage/Power Influence

Part No.

DescriptionApprox. Size

3" x 2" x 1.5"
    (7.6  x 5.1 x 3.8 cm)

P15173Protected HDR

12.5" x 3" x 2 5/8"
    (31.8  x 7.6 x 6.6 cm)

Paralleling electric power lines can induce AC interference voltages and currents onto metallic telecommunication facilities. The result is noise or operational problems to the circuit on these wires. An HDR bridged onto the wires, with its third wire connected to ground, provides a path-to-ground to drain those longitudinally induced AC interference voltages and currents. This is done while providing negligible loss to the circuit. The HDR is a relatively light duty reactor that is most effective at the harmonics of 50/60 Hz. Therefore, it is usually used with a Noise Choke, an INT, or to supplement a TEN. Its use as a “stand alone” device is usually limited to draining electrostatic voltages from wire line facilities. An HDR can normally be used on a carrier facility without seriously affecting the carrier signal.

The HDR is available in two configurations. The P15168 has a weather-resistant plastic case and a 36 inch long, jacketed, three conductor, 22 gauge wire lead. The red and green conductors are the line connections, while the yellow conductor is for the ground connection. Since it contains no protection of its own, the P15168 should only be used where station protectors or other protected equipment is located. The P15173 is an HDR mounted on an anodized aluminum support bar along with a 3-element gas tube protector in a weather-resistant plastic housing. The binding post terminals of the protector provide the point of connection to the line and ground.

Installation Notes

The HDR is connected to the circuit by bridging the tip (Green) and ring (Red) of the HDR across the tip and ring of a cable or wire line facility. The “ground” (Yellow) wire is then connected to a good earth ground, such as a power company multi-grounded neutral (MGN) or cold water pipe.

Placed at the far end of a noise choke equipped circuit, the HDR will provide a path for exciting currents to flow through the choke. This “turns on” the choke so it performs properly. The HDR will do the same for an INT if placed at the far end of the INT treated circuit, such as a subscriber line. This is especially true for 50/60 Hz harmonics. The HDR is often used in parallel with a TEN to supplement the TEN’s superior fundamental frequency (50/60 Hz) performance.

An HDR placed on an unshielded wire line can effectively drain electrostatic induced voltage-to-ground. It may require more than one HDR spaced along a line, depending on the length and severity of the exposure.

The P15168 is provided with two mounting holes in the plastic case, one at the top and one at the bottom. #8 screws are recommended for mounting. The P15173 is provided with two 7/16 inch mounting holes, one at the top and one at the bottom of the aluminum support bar.