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Induction Neutralizing Transformers

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Induction Neutralizing Transformers - INTs

“The Economical Solution to Induced AC Voltages, Currents or Harmonics”

An INT is a simple, passive device that splices in series with the cable. It is used to mitigate induced AC voltages, currents or harmonics that may be causing noise or equipment malfunctions or damages. Standard sizes are 2, 6, 12, 25, 50, 75 and 100 pair. Larger pair requirements use multiple configurations of standard sizes. IPTV DSL-T1 INTs are available for 1, 6, 12, 25 and 50 systems.

The use of neutralizing transformers dates back to before 1914. Today it continues to be one of the most effective means of solving a multitude of equipment malfunctions or damages caused by power line induced AC voltage and currents. In many situations, an INT is the only effective method of getting today’s sensitive, high-tech electronic devices to work the way they were designed to work in the real telephone world.

The INT is designed to reduce up to 95 percent of 50/60 Hz common mode or longitudinal voltages that may appear continuously on a telecommunication line or as transients from lightning, mechanical failures or switching operations on the power system.

INTs can provide up to a 30 dBrnc power influence reduction, which can yield similar noise metallic reductions depending on its location in the circuit. An INT works anywhere induced AC voltages or currents are causing noise or equipment malfunctions or damages.

Symptoms/Problems DSL-T1 Systems:

  • Regenerators Wiped Out/Blown CO Fuses/Repeater or Line Card Damage
  • IPTV DSL-T1 Shut Down Due to Lack of Power
  • IPTV Line Concentrators, Remote Switches or Subscriber DSL-T1 Systems Damaged During Storms and Surges
  • Steady-state 50/60 Hz Longitudinally Induced Power Line Currents or Voltages on the DSL-T1’s DC Power Feed Path, Which Affects the Power Regulators of the System
  • Unexplained DSL-T1 Failure Alarms
  • Excessive Bi-polar Violations/Bit Error Rates/Excessive Pulse Slip or Reframing
  • Unexplained Component Failure/Damages
  • Unexplained or Excessive Automatic Switching to Back-up or Alternate DSL-T1 Systems
  • Excessive Protector or Fuse Operations/Unexplained Total DSL-T1 System Failures
  • Steady-state AC Induced Voltages or Currents on the Central Office (CO) Terminal Equipment,
  • PBX or Key Equipment, Data Modems, Analog Inter-office or Subscriber Line DSL-T1 Systems.
  • Longitudinally Induced AC Voltages or Currents Caused by Switching Surges on Nearby Power
  • Lines or Lightning
  • Power Influence (Harmonic Induced AC Voltages or Currents) Levels that May Cause Circuit Noise
  • False Rings or Signals/Noisy PBX Trunks
  • Equipment Stops Working or Shows Electrical Damage with no Apparent Cause
  • Noisy Subscriber Lines, Trunk Lines/Wrong Numbers When Dialing
  • Non-IPTV DSL-T1 Circuits are Noisy or Analog Carrier System Doesn’t Function Properly
  • Burned-up Line Relays/Disconnects/Misdialings/Cutoffs

An INT contains multi-pair, telephone-type cable core, wound around a laminated steel core. The connected pairs go in and out of the transformer on a metallic basis. For example, tip wire in, through the winding of the transformer and tip wire out, thus providing DC continuity.

An INT placed in a cable facility and provided with an “exciting pair” (primary winding) for exciting current flow, will by transformer action produce an opposing or “180° out of phase” AC voltage that will be induced into the remaining pairs (secondary windings). This one-to-one turns ratio transformer action can cancel or“neutralize” up to 95% of the induced AC voltage that would normally appear at the end of the facility.

An INT is connected in series with a cable much the same way as a load coil or DSL-T1 repeater with the pairs running in and out. It doesn't matter which way they go ("in” may be toward the CO and “out” toward the field, or vice versa). It is important that all pairs go through the transformer in the same direction. If not, the effectiveness of the INT will be reduced greatly, and it may even cause the INT to turn off.

When treating a cable with INTs, it is best to treat all of the pairs in the cable. This is to minimize secondary induction, where the influence on the untreated pairs couples back into the treated pairs and negates the original INT treatment. This is particularly true when mitigating “noise” conditions. The voice frequency INT contains approximately 500 feet of unshielded and unjacketed 26 gauge cable. (The two pair INT contains about 500 feet of 24 gauge four conductor wire.)

Individual INTs are available in standard, off-the-shelf sizes ranging from 2 to 100 pairs. Custom design combinations are available for treating up to 900 pairs. Special designs have been provided for installation up to 3600 pairs. Standard open unit INTs are equipped with 24 inch long tails for in and out wiring, and are terminated in 25 pair 3M MS2 or AT&T #710 splice modules arranged with standard blue, orange, green, etc. color coded cable pair counts. Custom INTs are also available with solderless wire-wrapped type terminals or “quick-connect” punch-on type blocks. Steel, weather-proof enclosures are offered, as are fiberglass enclosures on special request. Also available are 2 to 100 pair INTs in sealed, gel-filled, polyvinyl enclosures equipped with 10 foot long gel-filled cable stubs. These units are intended for direct buried applications.

IPTV DSL-T-1 INTs (DINTs) are specially designed for use with IPTV DSL-T1 systems. They have two separate groups of pairs, one for each direction of transmission. The pairs are wound on the same core, but are separated by an electrostatic shield to minimize crosstalk coupling. Although IPTV DSL-T1 signals will pass through a standard INT, the attenuation and crosstalk coupling at the high frequencies of IPTV DSL-1 systems often make their use impractical. An IPTV INT, which is specially designed for lower loss and minimum crosstalk coupling, should be used on IPTV DSL-T1 systems.

IPTV INTs are available for treating 1, 6, 12, 25 and 50 DSL-T1 systems. Additional pairs are provided in the INTs for fault locating and order wire circuits. IPTV INTs work equally well on metallic voice frequency circuits. These circuits may be intermixed with the high frequency pairs of the DSL-T1 system.

The use of DINTs on IPTV span lines is not a new technology. Normally, DINTs are used to treat steady-state 50/60 Hz longitudinally induced power line currents or voltages on the carrier’s DC power feed path, or as a protection device from power surges and lightning storms.

DINTs are intended for placement on IPTV span line pairs that serve remote electronic devices such as IPTV Line Concentrators, Remote Switches, or Subscriber DSL-T1 Systems. They can also be used effectively on interoffice IPTV span lines to clear up problems such as excessive repeater loss, blown fuses, and temporary service interruption caused by switching back and forth between the main span line and the spare span line during lightning storms and power surges.

INTs Reduce Surge Current
How DSL-T1 Repeaters are Damaged During Power Fault

Induced voltage from a faulted power line will often damage series circuit components of repeaters in a DSL-T1 span line, even though the line is equipped with protectors from line to ground. Because the voltage-to-ground is often too low to operate the protectors, damage occurs to the repeater resistors, thyristors or power supply zeners as longitudinal current flows through the repeater.

For example, on a DSL-T1 route with paralleling power for two or three miles, the protectors at each end of the exposure will operate during a power fault. This causes a momentary low longitudinal impedance at each end while reducing the voltage-to-ground at the middle repeater to a level that is insufficient to fire its protectors. Damaging surge current flows through the circuitry of this repeater because the voltage-to-ground is not high enough to operate the repeater’s protectors.

A properly placed IPTV Induction Neutralizing Transformer (DINT) reduces the magnitude of surge current, saving repeaters and office fuses and keeping the system operational. By lowering induced AC voltages the neutralizing transformer also raises or lowers DSL-T1 powering voltages and reduces bit errors and system shutdown.


Weatherproof, vented enclosures are made of 14 GA steel, painted inside and out with gray-green enamel. Special fiberglass enclosures are available for corrosive areas. External clamps or captive screws secure the gasketed door. A hasp and staple are provided for padlocking. Watertight strain relief cable entrance bushings are provided for incoming cable stubs. Bushing allows up to two 1.10" diameter cables. PCM INTs come with two bushings that will handle 2" cable.


Part Number  
2 Pair
P15356 6 Pair
P15369 12 Pair
P15301 25 Pair
P15320 50 Pair
P15902 100 Pair
INTs Installed in Steel Enclosure

Letter after pair is enclosure size.

Part Number Size
P15573 2 Pair/B
P15579 6 Pair/B
P15584 12 Pair/C
P15730 25 Pair/C
P15595 25 Pair/D
P15759 50 Pair/C
P15913 75 Pair/C
P15770 100 Pair/C
P15606 100 Pair/D
P15739 150 Pair/D
P15705 200 Pair/D
P15768 300 Pair/E
P15772 400 Pair/F
P15417 900 Pair/H

M=MS2 Splice (pluggable) Modules (3M)

INTs For Direct Burial

Installed in Polyvinyl Enclosure With (1) 10 Foot Stub

Direct Burial INT
Part Number Size
P15300 25 Pair
P15318 50 Pair
P15922 75 Pair
P15904 100 Pair