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What Is a Ground Loop?

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • Through grounding, the safety of the user and the equipment or circuit can be ensured.

  • Ground loops can cause many issues.

  • A ground loop acts as an antenna that picks up electromagnetic energy, causing noise interference that disrupts the quality of the signal.

Ground loop

When two electrical devices are grounded using the same cable, and the structure is also grounded by connecting it directly to the earth, two paths are formed that build a ground loop.

Have you ever heard an irritating hum coming from a sound system? In most cases, this noise is from the AC power lines entering the audio equipment. A ground loop is formed when pieces of equipment are all connected to a common ground through different paths in a sound system. The ground loop creates a path for the current to flow between different equipment grounds and back. The current flowing through the audio equipment ground causes humming.

In this article, we will explore what a ground loop is and how it can be eliminated.

The Need for Grounding

Ungrounded devices or circuits pose issues of large static charges. In an ungrounded system, large static charges can build up due to insulation leakage. There is a fairly high chance of getting a shock when touching these circuits. On the availability of a conductor at a lower potential, there is a good chance for high static charges to discharge, causing thousands of ampere currents to flow, which can damage the system. Through grounding, the safety of the user and the equipment can be ensured.

Ideal Ground

In electrical circuits, current flows only if there is a closed path. A return path must exist for the current to flow back to the source. The return path is provided by a common point, called ground, in circuits.

Ideally, there is no resistance or parasitic capacitance in ground connections. The circuit components are connected to the ground and are assumed to have the same potential. In ideal cases, the absence of potential difference in the ground prevents the current flow. However, this is not the case in reality.

Typically the common ground potential is only true in books or models. Practically, non-idealities such as resistance and parasitics of the wires that lead to the difference in the ground potential exist. The non-idealities cause the difference in ground potentials and circulating current flow. 

What Is a Ground Loop?

When two or more points in an electoral system normally at ground potential have alternate connections through conducting paths, they form a ground loop. The presence of different ground potentials of such interconnected grounds is detrimental, as this condition involves potential difference that allows current to flow between the circuit grounds through the loop. 

Ground Loop Formation in Circuits

There are numerous ways in which ground loops are formed in circuits:

  1. Consider a shielded cable in which the drain wire is connected to the local ground at either end. There will be a ground connection already made by a conductor inside the cable. In this shielded cable, two wires are connected to the ground, taking two connecting paths and forming a ground loop. Depending on the wire parameters, the circulating currents flow in the loop.

  2. When installing electrical devices, we provide device grounding and grounding of the structure or foundation where the device is kept. When two electrical devices are grounded using the same cable, and the structure is also grounded by connecting it directly to the earth, two paths are formed that build a ground loop.

  3. In data logging, conductors such as sensor cables, power lines, or communication devices are connected to the ground. If any of these cables connect to the same endpoint, they form a ground loop.

Effects of Ground Loops

Ground loops can cause many issues, including:

  1. The ground loop acts as an antenna, picking up electromagnetic energy and causing noise and interference, disrupting the signal quality.

  2. The antenna effect of the ground loop can create surges, damaging the electronic components or circuit.

  3. Leakage currents flowing between devices sharing common ground produce detrimental effects on the components and measurement systems.

  4. There is a reduction in the dynamic range of digital signals due to offsetting in the ground voltage. The susceptibility of digital signals to interference is more under this condition and adversely influences digital communication.

Cadence’s suite of design and analysis tools can help you design circuits without the detrimental effects of ground loops. With Cadence software, it is easy to develop circuits free from design vulnerabilities such as ground loops, interferences, and parasitics. 

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