17.10.2 Detrimental effects
The harm from a ground loop can be seen in different ways. One consideration is the
electromagnetically induced effect. This will manifest as an AC noise or pulse. As seen in
(p. 134) the parallel conductive paths form an electrical loop that acts as an antenna to pick
up electromagnetic energy.
FIGURE 17-1. Stray AC magnetic fields picked up in loop antenna
l
Relatively small electromagnetic energy: This could come from AC current on a nearby
power cable, or RF energy transmitting through the air, and can cause electrical noise that
either corrupts an analog signal or disrupts digital communications.
l
Larger electromagnetic energy: The antenna loop scenario can have a more damaging
effect when a large current is discharged nearby. The creation of an electromagnetic pulse
can induce a surge that damages attached electronic devices.
Another way ground loops affect a system is by allowing ground current to flow between devices.
This can be either a DC or AC effect. For various reasons, the voltage potential between two
different points on the surface of the earth is not always 0 V. Therefore, when two electrical
devices are both connected to a local earth ground, there may exist a voltage difference between
the two devices. When a cable is connected between the two devices at different voltages,
physics dictates than an electrical current must flow between the two points through the cable.
See
17. Tips and troubleshooting
134