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I'm new to electronics so please bear with me.

I'm stripping a USB cable that I want to connect to another component - a 5V fan for example.

On the side pictured, i'm connecting up to a 5V fan. And on the other side is a regular USB connector which will plug in to a 5V DC power supply.

After stripping, I have noticed there is a outer wire running along the cable. On the left of the picture:

enter image description here

From my searching i've found this is a shielding wire. Is this correct? In the case where i'm not looking to shield and only provide power supply (not even use the data wires) what should I do with this extra wiring of the shield? I have heard that shield should be grounded. So should I:

  1. Combine shield and ground wire
  2. Ground shield wire separately
  3. Leave shield wire floating
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  • \$\begingroup\$ It depends very much what you are sending down the cable. If it's power only (e.g. 5V and GND) you can safely ignore the shield or use it as an additional GND. If you will be sending any kind of signal you should update the question with specifics. \$\endgroup\$
    – David
    Commented Apr 24, 2017 at 21:15

2 Answers 2

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Both options 1 and 3 are perfectly acceptable for power-only. If you want less noise on the power supply you should probably go with option 1 - tying the shield pins to the ground pin of the USB port. For signalling as well, 1 is the better option.

For power only, bear in mind you should not try to draw more than 100mA without negotiating with the USB host for more. Be sure to factor that in when deciding if the load can be driven by a USB port.

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  • \$\begingroup\$ This answer is great if one end will still be USB. I was unsure from the question, perhaps the original poster could clarify. \$\endgroup\$
    – David
    Commented Apr 24, 2017 at 21:18
  • \$\begingroup\$ thanks for the answer. @David, I have update the question but in short, the other side is a usb that will be powered by a power supply \$\endgroup\$
    – monokh
    Commented Apr 24, 2017 at 21:35
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To be as short and straight to the point as possible, number 3 is the easiest way to go. Given that you mentioned you won't b e using the data wires (green and white in your photo) and that the device being powered is not susceptible to noise, you can ignore the shielding (no need to connect the shielding to anything). I would advise you to trim it and put an isolating tape over it to avoid it touching any live circuits. Make sure you are no connecting any device that draws more current than your USB port can provide.

Good luck!

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