I N S T A L L A T I O N I N S T R U C T I O N S
Grounding
4.8
THE BASICS OF GROUND SYSTEMS (IMPORTANT)
1) MANY TYPES OF GROUNDS
Because there are several electrical systems in a broadcast facility, there are also several ground systems in the facility. Each
ground system fulfills a different function. Understanding these ground systems is important to be able to properly design and
debug an audio facility.
2) AC POWER GROUND
AC power wiring has a “hot” wire (typically 110VAC) and a “ground” wire. The ground wire is the return path for currents in the
“hot” wire. The ground wire is not a perfect zero resistance so a small 60 cycle voltage exists on the ground wire.
3) AC SAFETY GROUND (Equipment Chassis Ground)
The AC power system has a 3rd conductor which is a “safety” ground. This 3rd conductor is connected to the 3rd prong on the
AC outlet. On equipment with a 3rd prong on their AC plug, this safety ground is usually connected to the metal chassis of the
product. If something should happen that connects the “hot” 110VAC wire to the metal chassis of the product, then the safety wire
will throw the circuit breaker and the lethal voltage will be removed from the chassis. While there is usually no current on this
wire, it is often run in series to many parts of the building and is not a quality ground reference.
4) RF SHIELDING GROUND
The audio signal cables used to connect two or more pieces of audio equipment usually have a metal foil shield surrounding the
signal wires inside the cable. This metal shield protects the sensitive audio signal wires from electronic noise that would contami-
nate the audio signal. The shield is connected to a ground to drain the interfering electronic noise away from the audio signal. The
shield should always be grounded at one end only so as not to create a ground path between the connected equipment.
5) AUDIO SIGNAL GROUND... MUST BE KEPT NOISE FREE
Each piece of electronic audio equipment has an internal DC power supply which provides a DC voltage and a ground to the inter-
nal circuits. This ground is often called the “audio ground,” “circuit ground,” “signal ground,” etc. The internal audio ground is
connected to all of the various circuits inside the device. Whether the audio equipment is professional balanced equipment or
unbalanced consumer equipment, any noise that reaches the audio signal ground inside the equipment will be coupled into the
audio signal itself and appear at the audio output of the device. It is extremely important that the audio ground be as free from
noise as possible. This makes it important for the audio signal ground to not be connected to AC Power ground, AC Safety ground,
or RF Shield ground.
6) REAL WORLD SYSTEMS HAVE MIXED GROUNDS
In real world audio equipment, several ground systems connect to each audio device. Which ones are connected to the audio sig-
nal ground vary from product to product. Most consumer products are “double insulated” and do not have a 3rd wire safety
ground to introduce noise. However, most professional audio products connect the 3rd wire safety ground directly to the prod-
uct’s chassis and the audio signal ground which does introduce noise. In consumer products the cable shield ground is the audio
signal ground while in professional products, the cable shield may (or may not) be connected to the audio signal ground.