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. Digital carrier PCM 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 Carrier Systems:

• Regenerators Wiped Out/Blown CO Fuses/Repeater or Line Card Damage
• Digital Carrier Shut Down Due to Lack of Power
• Digital Line Concentrators, Remote Switches or Subscriber Carrier Systems Damaged During Storms and Power Surges
• Steady-state 50/60 Hz Longitudinally Induced Power Line Currents or Voltages on the Carrier’s DC Power Feed Path, Which Affects the Power Regulators of the System
• Unexplained Carrier 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 Carrier Systems
• Excessive Protector or Fuse Operations/Unexplained Total Carrier 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 Carrier 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-digital Carrier Circuits are Noisy or Analog Carrier System Doesn’t Function Properly
• Burned up Line Relays/Disconnects/Misdialings/Cutoffs

An INT contains multipair, 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 carrier 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.

Digital Carrier INTs (DINTs) are specially designed for use with digital carrier 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 digital carrier signals will pass through a standard INT, the attenuation and crosstalk coupling at the high frequencies of digital carrier systems often make their use impractical. A digital INT, which is specially designed for lower loss and minimum crosstalk coupling, should be used on digital carrier systems.

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

The use of DINTs on digital 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 digital span line pairs that serve remote electronic devices such as Digital Line Concentrators, Remote Switches, or Subscriber Carrier Systems. They can also be used effectively on interoffice digital 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.