# Understanding why daisy chaining causes ground loops in this setup

At this site, the star connection is recommended for daisy chaining. And in that context, it is written that one of the benefits is less ground loop effects.

This ensures each device will have the same voltage and current inputs. Troubleshooting is made more simple with direct wiring from the device to the power supply. Ground loops will be minimized with the star connection. Wavelength also recommends using the same length wires (for each device), twisted wires, and the shortest wires possible for the lowest noise setup.

Daisy chain:

Star connection:

What is the reason the ground loops will be more in daisy chain connection? Can this be explained visually with a diagram or SPICE simulation?

• The driver or controller controls a device. What is the chassis of the device connected too? As in, you are missing the connections to ground in the drawings for each device, which forms ground loops. Commented Nov 18, 2022 at 20:34
• Neither picture shows the presence of a ground loop. The site you linked is not that good. Commented Nov 18, 2022 at 20:53
• There's a very basic misstatement in what you quoted. Neither connection scheme ensures that each device has the same current. That is determined by the current needed/drawn by the devices, not by the wiring scheme. Commented Nov 18, 2022 at 20:59

Imagine each wire in your diagram is a resistor (which, practically, it is.) When you pass current through a resistor, you see a voltage drop.

The greater the current, the more the drop. The greater the resistance (that is, the longer the wire), also, the more the drop. That’s why this voltage is called an ‘IR drop’, as it’s proportional to both current and voltage, that is, E = IR.

When loads are wired in series (‘daisy chain’), the load currents add up in the wires, increasing the IR drop. And their wire resistances add up too, also increasing IR drop. Thus, the farther the load is down the loop, the more its IR drop.

Star wiring limits the drop to just the single home run from the power supply to each load. So the load currents don’t add up, nor do the wire resistances.

Your diagram doesn’t show a shared signal ground reference, but the nature of question implies one. So let’s clear that up. A ground loop is formed when a power return shifts from the ground reference, and there is some kind of path between that return and ground.

So if signal ground and power return are naïvely connected or related to each other within the devices, the return current will divide between the ‘return’ and ‘signal’ paths. That’s a ground loop, in a nutshell.

The star scheme reduces IR drop, and so will see less of a ground loop should it be an issue due to poor system design. But it doesn’t address the root cause: power supply return current making its way onto signal ground.

• You explain their first argument "This ensures each device will have the same voltage and current inputs." I understand that. But ground loops are 50/60Hz coupled magnetically. My question is specifically about their ground loop argument.
– GNZ
Commented Nov 18, 2022 at 20:24
• Ground loops aren’t ‘coupled magnetically’ - they’re formed by an unwanted leakage path from the supply and/or return wires to ground. You can fix this by making the 'ground' as low impedance as possible (like, solidly bolt everything to the chassis) or running 'signal ground' separate from 'power ground'. Commented Nov 18, 2022 at 22:01
• Is it possible to draw your argument "A ground loop is formed when a power return shifts from the ground reference, and there is some kind of path between that return and ground." showing the loop ect. I cannot picture that sentence. It would be great if you can draw and show such loop.
– GNZ
Commented Nov 19, 2022 at 14:15
• At this point it would be helpful if you would provide more information about the devices you’re referring to. Then a meaningful discussion can ensue. Commented Nov 19, 2022 at 15:05
• Im referring to the diagram in question: i.sstatic.net/NBnqk.png Can you show/draw the ground loop on that?
– GNZ
Commented Nov 20, 2022 at 19:40