What is a Line Isolation Unit 

A Line Isolation Unit (LIU) connects between your music source and your telephone systems such as the Private Automatic Branch Exchange (PABX) and is required by law for all music on hold hardware prior to use. Line Isolation Units can come in different forms and they can be quite basic, or more advanced, such as the RB-LI2 stereo ISU which has more features.

The cost of each of these can vary from $20 for the basic LIU to $400+ for advanced ones like the RB-LI2.

Basic Line Isolation Units

Advanced Line Isolation Units

How does a Line Isolation Unit / LIU Work?

The basic LIU is connected to the phone systems or PABX and a 3mm headphone jack that is plugged into an On Hold Player. The diagram below shows an example of how the LIU acts as a bridge between phone system or PABX and the specified audio source. Once it’s installed the LIU isolates an audio source to a telephone system or PABX to provide background music and Music on Hold.

Also please note that most of the basic LIU’s can provide only a single connection to an audio source. If a second connection to another audio source is required, then as shown in the diagram below, another LIU is required to bridge this new audio source.

Basic Setup for a Line Isolation Unit

Why Is It Important?

A LIU is used to isolate audio signals from inter area ground loops which are a major cause of noise, hum and interference in audio, video and computer systems. The cause of this unwanted noise can be attributed to equipment being powered by different main power supplies, or different phases on the same supply.

_Disclaimer

_{We currently sell the basic LIU ($20 per unit) which uses a simple plug in connection, but please check whether your current phone system or PABX has an internalized line isolation unit and if so a phone technician may be required.}

alternatively electronic specialists like Altronics may also sell them locally.  http://www.altronics.com.au/p/a0642-telephone-line-isolation-unit/