DIY Extension Cord With Built in Switch - Safe, Quick and Simple

This neat little device solves three problems that I usually come across when experimenting or doing work around the house or out in the yard:

1) No matter how long your extension cord is, it's always three feet too short. My project adds six feet to any extension cord. If you build one you can make the cord as long as you want. Just remember to derate the power of the appliance accordingly.

2) No matter where your extension cord is, you can never find it. Now I have an extra one in case I can't find my other one or if the other one is in use.

3)Some appliances do not have an on/off switch. I am doing some experimenting with hydronic solar thermal collectors and the pump I'm using does not have an on/off switch. To control the pump I have to plug or unplug it, which is annoying. Other things that usually don't come with switches are soldering irons and hot glue guns.

This project is safe because all materials used are CSA approved, the device is properly grounded, wires are properly sized and an appropriate strain relief device is used on the cord.

This project is quick; it only takes about 15 minutes to complete.

This project is simple with only a few components and straight-forward wiring.

There are only a few materials and tools required, most of which are redily available at your local building supply store:

A double gang PVC conduit box with one conduit entry
A single pole switch
A 120 volt recepticle
A combination switch/receptical wall plate
A 1/2 inch threaded bushing
A 1/2 inch threaded nylon dome connector
Some 14 gauge crimp-on ferrules
Six feet or more of 14/3 SOOW cable
A 120 volt 15A extension cord male plug

The nylon dome connector and ferrules my be a bit difficult to find. I order them online from elecdirect.com and have a couple left over from my greenhouse automation project. You should be able to get them from your local electricial supply store if you can't get them from your local hardware store.

All materials cost about $30

Remember that the hot wire (black) always goes under the brass colored screw, the neutral wire (white) always goes under the silver colored screw and the ground wire (green) always goes under the green colored screw. In the interest of self preservation, you might want to make absolutely sure that you properly ground this device.

Remember that the wire can only be inserted under the screw terminal in one direction. Insert the wire in the direction that the screw rotates with tightened. That way the screw will draw the wire in rather than push it back out.

The device box has a 1 inch hole in the bottom. The first bushing goes in with PVC conduit glue and reduces the hole down from 1 inch to 3/4 inch.

The second bushing goes in with PVC conduit glue and reduces the 3/4 inch hole down to a 1/2 inch female thread.

The nylon dome connector goes in last. It has a 1/2 inch male thread that screws into the second bushing. Remember to use the rubber o-ring that should come with the nylon dome connector (yellow in the pictures).

Once the nylon dome connector is in, feed enough SOOW cable through it and tighten the nut on the dome connector until it clamps down on the cable tightly. This should provide strain relief for the cable. If something tugs on the cable, it will tug on the clamped portion of the cable and not on the electricial connections inside the device box.

Crimp a 14 gauge ferrule onto each of the three wires coming into the box. The ferrules are necessary because the terminals of the switch and the recepticle are not designed for stranded wire, only solid wire. The ferrule "converts" the stranded wire to solid wire at the terminals. If you cannot find any ferrules, another option is to use a GFCI protected, outdoor rated recepticle and no switch. The terminals on a GFCI protected recepticle can accept stranded wire. You can use the "test" and "reset" buttons to switch your device on and off.

The incoming ground and neutral wires go straight to the green and silver colored screw on the recepticle, respectively. The hot wire goes into the switch and then carries on (through a short jumper wire) into the brass colored screw on the recepticle.

The mounting screws on the switch and recepticle have a small square of vinyl holding them in place (see photo 4). This must be removed before securing the devices to the PVC box. The removal of the vinyl square will allow the ground from the recepticle to be carried over to the switch through the brass grounding bar in the PVC box.

After mounting the devices, put the wall plate cover on and you're done!

Now you can plug your things into the outlet and control them with the switch. Just as a demonstration I included photos of my drill press plugged into the device. The lamp built into the drill press can be controlled with the switch on the device. By flicking the switch you are essentially plugging or unplugging the drill press.

Well that's about it. I hope I've given you enough information to build your own switched extension cord. As always, thank you for reading and please don't hesitate to share your questions, comments and constructive criticism.