I have a camera that uses a USB cable to connect to my computer. I want to extend the cable from 3ft to about 6ft. Originally I just created my own cable, soldering 4 26AWG wires to a blank USB connector and connecting the other side to the correct leads on the camera (this cable shown on right in the photo). The original wire (shown on the left in the photo) has slightly smaller wires probably either 28AWG or 30AWG.

When I plugged the new cable in, the camera would not come up and my computer said it was drawing too much power. So I tried just extending the original cable by just splicing additional wire before the connector. Once again I used they 26AWG wire.

With the extended original cable, the camera still does not show up, and it also does not give the warning that it is drawing too much power.

I am not sure what is happening. Given that the original cable extended does not work I am guessing that either the increase in wire gauge or the added length is causing an issue, but I do not understand why. If anyone has context on this it would be greatly appreciated!

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    $\begingroup$ INteresting, wouldn't it have just been eaiser to find a compatable cord $\endgroup$
    – LazyReader
    Commented Jul 25, 2021 at 2:42
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    $\begingroup$ Not only are you missing shielding but you won't have the correct cable impedance. At USB speeds, everything is a transmission line. Individual unshielded wires won't work. $\endgroup$
    – Transistor
    Commented Jul 25, 2021 at 9:11
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    $\begingroup$ The USB specifications are freely available. Did you check that your cable meets the requirements laid out on the specifications? $\endgroup$ Commented Jul 25, 2021 at 9:29
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    $\begingroup$ It looks like the most relevant specifications for you are USB 3.1 Legacy Cable and Connector which defines the requirements for the connector and cable, and Universal Serial Bus 3.1 Legacy Connectors and Cable Assemblies Compliance Document, which outlines additional testing procedures to ensure functionality of the cable. $\endgroup$ Commented Jul 25, 2021 at 9:46
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    $\begingroup$ What you did here would have worked perfectly well in the days of RS232 serial cables at 9600bps or 19200bps. It's a different world now. $\endgroup$ Commented Jul 26, 2021 at 3:16

4 Answers 4


Even aside from the fact that no outer sheath and no shielding makes me cringe, there are a couple of big issues with your custom cable:

  • The data lines (pins 2 and 3) need to be a twisted pair. Period. USB uses differential signaling, and at the frequencies involved, the signaling lines need to be a twisted pair so that they actually behave correctly.
  • The cable might be too long. 6 feet is within spec for a properly made cable, but with what you’ve got there you can only realistically expect maybe 6 inches to work.
  • The cable absolutely should not be coiled like you have it. Any coil of wire with current going through it is an inductor, and that will cause serious havoc with your power draws (and possibly heat itself up to the point of melting the insulation or starting a fire if you’re not careful, this is a serious hazard actually with extension cables).

All in all, you are almost certainly better off just buying a USB 2.0 cable long enough for what you need, and then cutting off the far end and putting in the correct connector type for your application. Alternatively, you can get a 6.5 foot USB 2.0 extender cable (type A plug on one end, type A port on the other) for less than 10 USD on Amazon, and then you don’t even have to mutilate a cable, you can just use the extender with the cable that came with the device and be done with it.

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    $\begingroup$ I would be surprised if inductance on the power lines caused any problems on a DC load unless the load was pulsing current and had no local supply decoupling. There's enough air-cooling in the photo setup there to prevent excessive temperature rise. I agree that the setup won't work due to other reasons listed. $\endgroup$
    – Transistor
    Commented Jul 26, 2021 at 3:39
  • $\begingroup$ @Transistor Agreed. The coil will cause interference though and muddle the signal. The wavelength of a couple GHz is a couple of cm (I cannot exactly find the nominal maximum frequency of a USB 3.1 signal). $\endgroup$ Commented Jul 26, 2021 at 5:10
  • $\begingroup$ Thank you for the information, I was unaware of the specifications of USB cables (but no need to add the part about you 'cringing' given that I posted this question to learn). I ended up using 2 USB cables spliced together and that worked and ended up being log enough. $\endgroup$ Commented Jul 27, 2021 at 18:45
  • $\begingroup$ At least for USB hi-speed (introduced with USB2) and over some distance like a meter, I'd say the impedance of the twisted pair (which varies with diameter of insulator and other parameters) also matters. It's nominally 90 ohm, and that matters to damp reflexions. Independently, if the data wires are a twisted pair of the right impedance, then there is no problem whatsoever with all (or part) of the wires forming a coil. Experiment: make a coil with a regular USB cable, it still works perfectly fine. $\endgroup$
    – fgrieu
    Commented Jul 27, 2021 at 23:07

The most prosaic reason why your cable doesn't work and is drawing too much current is that you connected he wrong pairs of pins and/or some of the the wires are shorted together.

If that is not the case, there are two obvious problems:

A USB cable that meets the specifications has two twisted pairs of connectors enclosed in an outer shield, not four wires flopping about anywhere.

The left hand cable has also an RFI suppressor (the "bulge" in the cable). Yours does not. Since RFI suppressors cost money, there is presumably a good reason why it is there.

USB cables are pretty cheap. Trying to make your own isn't a good idea unless you have a very good reason for doing it.

FWIW USB 2 specifies the maximum length of a cable as 5 meters. USB 3 has a functional specification for the signal propagation along the cable rather than just giving a maximum length, but in practice the maximum length is about 3 meters.

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    $\begingroup$ Well, there is a good reason for the RFI suppressor: FCC approval. It filters high frequency noise but as a side effect blunts the edges of the signal, making it worse so that the radio it emits doesn't have such a high amplitude. If you have connection trouble try removing the ferrit bead. It's worth a shot. $\endgroup$ Commented Jul 25, 2021 at 23:29
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    $\begingroup$ FWIW I have seen communications failures when going from a 15-inch to a 2-meter USB-C cable. Granted this can depend both on the quality of the cable and the robustness of the signal drivers at both ends of the link. $\endgroup$ Commented Jul 26, 2021 at 12:55

For the USB signal, you have to make a 90 Ohm characteristic impedance twisted pair. The characteristic impedance depends on the insulator and on the outer/core diameter ratio of the wires. Search online calculators on the net.

A simple way to twist wires:

  • connect the two wires making a long wire
  • twist the wire using an electrical drill
  • put the wires parallel keeping the wires taut
  • let them twist together

It is also possible to twist the two wires independently in the same direction, before letting them twist together.

Also, the max. length of USB signal twisted pair is around 5 m.


The device is likely not getting the power it needs.

Use a thicker wire to ensure the resistance is the same as the original.

Don't make an induction coil with your cable. It also helps to use twisted pair - see some of the faster ethernet cables for reference. You twist the two ends of a corresponding signal to preserve integrity. Since an approximately same magnetic field passes through in the opposite direction at the next twist, it helps cancel out the field's noise.


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