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Isolated Ground Circuits

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Isolated Ground Circuits for Audio Systems Explored

Isolated Ground Circuits:

Basic AC electrical requirements for an audio system require a special circuit called an “Isolated Ground” or “IG Circuit”. These circuits are only part of the special needs for a properly installed audio system. I would like to review what an isolated circuit is, how it works, and the associated problems with relying on one by itself to provide power quality.

A properly installed IG circuit separates the Equipment Ground from an Isolated Ground originating from a ground rod directly to the receptacle ground. At no point in the overall IG circuit can the Electrical or “chassis” ground contact the isolated ground. Special IG receptacles are required at every plug location. In theory, by separating the equipment ground from the isolated ground we have provided a “clean ground” for the circuit. This clean ground is NOT connected to any other equipment or chassis ground from the initial neutral to ground bond all the way to our audio equipment connected to the IG receptacle.

By not interconnecting the isolated ground to the equipment ground we can isolate stray currents and therefore voltages on the isolated ground. These currents can show up on the audio system as noise or hiss.

The IEEE definition states in IEEE 1100-1999 section 8.5.3.2 an Isolated Ground circuit is:

“…grounding configuration that is only intended to be used for reducing common-mode electrical noise on the electrical load equipment circuit…”

This definition does not indicate that an IG circuit provides power quality for under voltages, sags, swells, or voltage transients. It is very difficult to establish and maintain an IG circuit. Once the Isolated Ground and Equipment ground leave the neutral to ground bond they can no longer touch. This isolation is further complicated by the fact that some manufacturers do not keep the IG and EG isolation internal to their equipment. The more equipment and receptacles that are on the isolated circuit can lead to many other places where you loose the isolation and degrade the IG circuit. Standard receptacles DO NOT have the Isolated Ground separated from the Electrical or Chassis Ground. Special receptacles are required for IG circuits.

Isolated Ground Circuits can help provide substantial noise attenuation, however, for complete power quality they must be properly installed. In addition, you should install surge suppression, noise suppression, harmonic cancellation, voltage regulation, and uninterruptible power supplies to protect from under voltages, over voltages, sags, swells, and voltage transients.

I have witnessed many electrical nightmares in my 23 years of Church installations. The most common mistake a church can make is having “Joe the shade tree electrician”, who is a member of the church, do the electrical installation. This is 99% of the time a bad idea. It may save the church a few dollars but can cost sound quality and possibly cause equipment damage. I always recommend hiring a commercial electrician that is licensed in the state your church is located. You should also choose an electrician that has experience installing IG circuits for an audio system if possible. I would never let an electrician experiment with my electrical system. A professional commercial electrical company should know exactly what an IG system is and how to configure one for your facility.

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