Confusion regarding ground loops.

WBahn

Joined Mar 31, 2012
26,398
apples and oranges, we see this very differently. (picture of grounds in post #5)
I would never have thought that reducing ground and power resistance would increase ground current measurably. The current is a function of the load not a function of ground resistance. Even if the current went up by 0.1% the greatly reduced resistance would cause the induced voltage to be much smaller. Ohms law give me the idea that as resistance approaches zero the voltage approaches zero and thus less effect.

You must be talking AC not DC.
I have never added resistors and inductors to grounds. I have added inductors to power and data lines to isolate RF noise.
To try to support your point, I have used common mode chokes on power lines and long runs of cables, to keep RF off the wires. In these cases the "grounds" have a area or length greater than 1/4 wave length and I am not fighting ground resistance but ground inductance or impedance at 100s of MHz or ghz. Even in this case lowering ground resistance from 0.1 ohm to 0.01 ohm will not measurably change the current in grounds.
The TS very specifically asked about ground loops. The Post #5 does not have any ground loops in either situation shown. The issue being addressed there is not a ground loop, but rather ground bounce.

When you have added inductors to power and data lines (and you can also add them to ground lines, as well, but you need to be more careful if you are using single-ended signals referred to the system common) you are doing exactly what I described, increasing the resistance (impedance) at the offending frequency in order to reduce the interfering currents at that frequency.

EDIT: Fix typo.
 
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MisterBill2

Joined Jan 23, 2018
8,983
Using a power return path for connecting signal return points is always a poor choice. That is the basis for having a "star point" arrangement. So adding impedance to ground connections is only useful in a system that is already seriously flawed. And serious flaws are rather common and seldom very obvious. The point is that at no time and under no condition should a power return path and a signal return path be the same. While they may not be actual ground loops the effect is the same and the solutions are similar.
 

WBahn

Joined Mar 31, 2012
26,398
Using a power return path for connecting signal return points is always a poor choice. That is the basis for having a "star point" arrangement. So adding impedance to ground connections is only useful in a system that is already seriously flawed. And serious flaws are rather common and seldom very obvious. The point is that at no time and under no condition should a power return path and a signal return path be the same. While they may not be actual ground loops the effect is the same and the solutions are similar.
Ideally you are correct -- but there are situations in which other considerations force them to be the same. Sadly, many of those situations also reduce the available mitigation options.

Even when the intended signal and power return paths are separate, ground loops in just the power return paths can result in noise pickup that gets coupled into nearby signal paths, particularly if the effective areas of the two antennas are large or overlap.
 

MisterBill2

Joined Jan 23, 2018
8,983
A "ground loop" is an invisible nemesis that couples various ground symbol points together with an unknown and often variable series resistance back to the power supply common return point. If a noise current is flowing through thhe same resistance as a signal current then the voltage will result from the sum of those currents. Thus the cause is known, at least in principle. The exact mechanization is often not that obvious. So avoiding the problem takes both effort and insight, in addition to following procedures.
 
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