Introduction: Power/Effort Saving PC Extension Lead

Fed Up of having to switch off all your PC peripherals individually?

there are several commercial solutions however all are quite expensive, most have a "master socket" witch activates the other sockets when it is put under load, this would require some complex smarts, however I found one that is activated by your PC's USB 5V supply witch gave me the idea for a simple DIY solution

Step 1: Materials and Tools Required

  1. A relay capable of being activated by a 5V signal and switching the AC supply, I used a SSR-25 DA solid state relay, a traditional relay would do just as well. The SSR-25 DA can switch 24-380VAC at 25A and is triggered by a 3-32VDC signal, it cost me £4.25.
  2. A USB cable of some sort, all you need is the standard end that plugs into your PC, I used a 30cm USB A to B cable and cut off the B end, ideally one a bit longer would have been better but its what i had. If your feeling posh you could put a connector on the extension lead and save cutting into the cable.
  3. Assorted electrical tape, heat shrink and cable ties.


  1. Wire stripper
  2. Wire cutter
  3. lighter for heat shrink
  4. Screw driver for wiring the plug and doing up relay contacts
  5. depending on your relay you might need to do some soldering

Step 2: Mains Side

First Remove the plug of your extension lead.

Make a cut in the sheath of the extension cable where you want your relay to be, it can be tricky to avoid nicking the inner cables, bending the cable and thus stretching the sheath helps.

Pull out a loop of the live wire (Brown in the UK) and cut it so there is enough left sticking out to connect to your relay, then make a second cut in the sheath the distance between the relay contacts and pulled the other end of the loop back through.

Then slide the sheath back into place, and put some heat shrink over that section to hold it in place.

Next strip the end of your two protruding wires and screw them onto the relays load terminals.

Then simply replace the plug, you will have to cut a few inches off the end of the flex to account for the live wire being pulled through a bit.

Step 3: 5v Side

Cut the none standard USB end of your cable and strip back the outer cover, being careful of the extremely thin inner wires.

Connect the red to the positive signal terminal of your relay, and the black to the negative, if your using a traditional relay connect them to the coil pins, polarity doesn't matter.

Cut of the white and green data lines and cable tie the wire to some thing for strain relief (my relay had a handy mounting hole).

Step 4: Test and Finish Off

Try it out!!

Test the 5v side first before plugging in the extension lead, my relay had an LED to show if it was activated, you should be able to hear a traditional relay click on as you power the USB lead.

Test the mains side (live mains electricity, No finger poking, Safety first, etc) I used a lamp and simulated the PC powering on and off by unplugging and re-plugging the USB lead, the lamp should light when the USB lead is plugged in.

Finish it off

I would recommend putting the relay in a insulated box of some kind so you don't electrocute yourself (mine lives behind a cupboard so i didn't bother).

I wrapped the live side of the relay in electrical tape and cable tied it to the sockets and then wrapped the whole thing in tape and poked holes for the socket I had covered.

Use it

Plug all your PC peripherals into the sockets and the USB cable into your PC, all the peripherals will have the power cut when the PC has shut down and power back on when it boots.

Home Technology Contest

Participated in the
Home Technology Contest