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Is it beneficial to twist the red/green power/ground wires from a low-voltage (~5V), relatively low current (1 to 5 A) switching, desktop power supply?

This makes my wire bundle on a desk less chaotic, but will it reduce noise or provide any other benefit? Is there any reason why I should specifically avoid doing this?

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    \$\begingroup\$ twisting the wires has useful effect, in addition to the many answers and comments, of reducing the inductance of the 2 wires. Thus the power supply output capacitors are just a few nanoHenries (ok Dozens of nanoHenries) away from your load, instead of several microHenries with untwisted wires. \$\endgroup\$
    – analogsystemsrf
    Commented May 17, 2019 at 3:14

4 Answers 4

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Twisting wires reduces the magnetic loop area of the wires, this has two implications:

  1. Reduced susceptibility to noise from magnetic fields, with twisted wires an a smaller magnetic loop area, external magnetic fields will induce less current in the loop made by the wires than straight cables.
  2. Reduced magnetic radiation from loads that are switching. A magnetic loop is an antenna, switching loads and changing currents cause the antenna to radiate magnetic radiation, which can cause noise in other devices.

Generally its a good idea to twist the wires and reduce the radiation and susceptibility to noise.

I can't think of any reason why you wouldn't do this, on all of my prototypes/products I make sure the wires are twisted.

enter image description here

In the image above the magnetic loop area of a straight cable is large, a twisted cable the loop area is similar, but the adjacent loops magnetic contribution cancel each other out.

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    \$\begingroup\$ Not only does the twisting reduce the loop area, but more importantly every twist of the cable introduces adjacent areas of opposite polarity for a given field. In on other words the emitted or received noise of adjacent loops cancels each other. The twisted pair diagram should show alternate arrows in the opposite direction. \$\endgroup\$
    – scorpdaddy
    Commented May 16, 2019 at 19:25
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    \$\begingroup\$ In addition, a twisted pair has got a higher capacitance than two independent wires since they are forced to be quite as close as possible to each other, which could have a slight positive effect when it comes to attenuation of high-frequency distortion or noise... \$\endgroup\$
    – aschipfl
    Commented May 16, 2019 at 19:45
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    \$\begingroup\$ @scorpdaddy there are two ways to draw this, one flips the current and keeps the magnetic field straight, the other flips the magnetic field and keeps the current straight, you can't have it both ways. \$\endgroup\$
    – Voltage Spike ♦
    Commented May 17, 2019 at 2:52
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    \$\begingroup\$ try 8 ~ 12pF per foot \$\endgroup\$
    – Tony Stewart EE75
    Commented May 17, 2019 at 5:42
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    \$\begingroup\$ How much additional wire length do you need for twisted pairs vs. untwisted and how much thicker does it get? Could be important for some applications. \$\endgroup\$
    – Michael
    Commented May 17, 2019 at 6:33
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It would reduced radiated noise. No specific reason to really avoid it since the only real reasons are reduced heat dissipation and overkinking the cable which shouldn't happen if you do it properly.

It would also reduce noise that is coupled to the lines that enters the power supply (by ensuring the noise is picked up "identically" on both lines), but that barely matters at all for something like the kind of power supply you probably have.

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  • \$\begingroup\$ It'll reduce susceptibility to radiated interference, too, but it would be a strange work environment where that could make a difference. \$\endgroup\$
    – TimWescott
    Commented May 16, 2019 at 18:49
  • \$\begingroup\$ @TimWescott Yes, radiated noise from the power supply is already unlikely to be an issue, let alone the power supply itself being vulnerable to external radio interference which is why I didn't mention it. \$\endgroup\$
    – DKNguyen
    Commented May 16, 2019 at 18:53
  • \$\begingroup\$ This answer should be corrected to indicate that twisting reduces radiated noise and susceptibility to incoming noise. \$\endgroup\$
    – scorpdaddy
    Commented May 16, 2019 at 19:23
  • \$\begingroup\$ It could indirectly increase radiated noise, since two separate wires can act as a choke - while they also act as a magnetic antenna, whatever is downstream of the choke might be a better antenna or in a more deleterious place for an antenna to be. \$\endgroup\$
    – rackandboneman
    Commented May 17, 2019 at 15:23
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Twisting power and return lines together will not cause an adverse affect electrically. Also, any high frequency noise that happens to exist on those lines will radiate less, though maybe only marginally less, due to a tighter coupling between them caused by the reduced geometric separation of the conductors.

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    \$\begingroup\$ Twisting the lines reduces 50-60 Hz noise as well as high frequency noise. In test it shows substantial reduction of emissions and susceptability that is not offset by reduced geometric separation. \$\endgroup\$
    – scorpdaddy
    Commented May 16, 2019 at 19:21
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More twisting means more contact surface betwen magnetic radiofrequencies polarities which can be assumed as less output voltage as the twisting decreases conductance ratio developing a closed magnetic field which converges to more inductance. eventually showing a predictable extra current than driving a bare load with no twisting at all... Interestingly the ammage vs inductance reciprocal isn't a straight line but an exponentiation such as at the end of a twisting pair of cables would turn a 1 Ampere load maybe into 1.8 amperes breaking some current loops in the planned circuitry...

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