Mutual Drainage Reactor Module

The Mutual Drainage Reactor Assembly is intended to replace the standalone drainage reactor used primarily in the Central Office (CO) of a telephone company. The Mutual Drainage Reactor Assembly is comprised of a module (Model 751300) and a shelf (Model 751201).

As a modular, plug-in arrangement, this system offers a neat and organized installation in a CO.

Product Number CLEI Code Description Download Documents
751300 NPDT4002AA Mutual Drainage Reactor Module Installation Guide

The Mutual Drainage Reactor module

The Mutual Drainage Reactor module, Model 751300, is designed to protect communications equipment against the high voltages which may be induced onto telephone pairs, within a telecommunication cable, during power fault conditions.

The Mutual Drainage Reactor Assembly provides a direct drainage path to ground for common mode induced voltages while maintaining a high impedance to AC differential telephone signals (typically 60 to 4000 Hz). The result is safe, uninterruptible communication before, during, and after fault conditions. It is ideally used on class “A” circuits.

NOTE: Please note that the installation procedure from the installation guide has been updated.


  • When the module is connected across a telephone pair with its center tap grounded, it presents a high impedance to differential (metallic) AC signals on the line while presenting a low impedance to ground for common mode (longitudinal) noise
  • The center tap may be grounded either directly or through a three element gas tube, depending on the application
  • The module’s two coils are wound on a single core, and are fully interleaved. Each coil consists of two windings, with the inner winding of one connected to the outer winding of the other to form one half of the mutual drainage reactor. This form of coil construction ensures good transient response, even to lightning induced surges on the line
  • High drainage capability without signal distortion is achieved by ensuring that the separate coils are perfectly balanced and tightly coupled, and are of sufficient impedance to give satisfactory longitudinal balance and insertion loss figures at audio frequencies
  • The module is encased in a plastic mold and is mounted on a plug-in module. Up to eight modules can be inserted in the 23-inch rack shelf to service eight different telephone pairs. Two terminal blocks at the rear of the shelf access the Tip and Ring terminals of each card


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