Ground Loops

A ground-loop in an electrical system, is an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, i.e., ground, but are actually at different potentials [ground conductors have some other value than zero resistance]. For example, the electrical potential at different points on the surface of the Earth can vary by hundreds of volts, primarily from the influence of the solar wind. Such an occurrence can be hazardous to personnel working on long grounded conductors such as metallic telecommunications cable pairs.
A ground loop can also exist in a floating ground system, i.e., one not connected to an Earth ground, if the conductors that constitute the ground system have a relatively high resistance, or have, flowing through them, high currents that produce a significant voltage (IxR) drop. Ground loops can be detrimental to the operation of the electrical system. Contrast with ground current.

There are three fundamental grounding techniques;
1. Floating Ground System: The ground plane is not returned to earth.
2. Single-Point Grounding System: A single physical point in the circuitry is designated as a ground reference point.
3. Multipoint Grounding System: The ground plane is taken to earth, effectively taking each point connected to the ground plane to earth.

Refer to MIL-HDBK-1857, Grounding, Bonding and Shielding Design Practices

A power plane at RF will act like a patch antenna, spreading spurious signals all over the Printed wiring board.
An unintended antenna connection.

Design Rules:
1: Stack power planes next to ground planes so they capacitively couple. Coupling the power plane to the ground plane reduces the number of by-pass capacitors required in the circuit.
2: When possible use wide traces for power and ground. Thicker traces reduce the trace impedance and allow the line to carry higher current loads.
3: Avoid placing slots in ground planes. Slots in ground planes force the current to flow around the slot, separating the return current from it signal trace. Slots may be placed at the edges of the board where signal trace aren't run.
4: Avoid Ground Loops when possible, and avoid ground loops in low-level, low-frequency circuits. A ground loop is an unwanted current loop. The current flowing in the loop generates additional noise and provides no benefit to the circuits operation.
5: Board Stack-up;

How components are grounded in a circuit should always be taken into consideration to alleviate potential problems or enhance circuit operation. For example if the adjustment lead of a 3-terminal regulator is grounded near the load, than fluctuations in the load ground will be translated back to the the three-terminal regulator, in effect making the regulator's ground connection a sense line. Of course that only works if the load is located near the regulator.

PWB External Etched Copper Current Capacity Chart: current rating based on trace cross section in square mils, temperature rise and current in amperes.
Chart of PWB Internal Etched Copper Current Capacity: current rating based on trace cross section in square mils, temperature rise and current in amperes.
Graphic of Minimum Annular Ring, What is a Minimum Annular Ring.
Graph of PWB Ground Potential, moving away from a single point ground connection [example].
Electronic Chassis Grounding

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Modified 1/9/12
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