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.

Step 1: Materials

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 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

Step 2: Wire Up the Extension Cord Plug

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.

Step 3: Thread the Wire Into the Device Box

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.

Step 4: Wire Up the Switch and Recepticle

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!

Step 5: Enjoy Your New Switch/Recepticle/Extension Cord Thingy

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.

5 People Made This Project!


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11 Discussions


16 days ago

Very Nice!! Great Photos and Instructions, l have made 3 similar to yours l did not post mine because they are in shop, however l used a GFCI- ground-fault circuit interrupter. Just in case.. Great Job!


2 years ago

So I love this! Thank you for posting. I was actually looking for something similar to this for a DIY desk lamp. It's basically the exact same thing you did, except it has a lamp attacked to the top.

So that's where im curious: if go the lamp route, I believe I would wire up the electrical outlet first with the black wire, then run a black wire to the Switch.

But where I'm stuck is how to connect the lamp to the switch. I don't want to do something that won't be rated properly or unsafe.


2 years ago

Great idea!! Would something like this pass electrical code? I'm guessing as long as the wires are the correct size for the power, and everything is sealed to prevent touching anything live, it should be ok - right?

1 reply

Reply 2 years ago

Generally speaking, an electrical device that isn't hard wired or intended for retail sale doesn't have to meet any code. All the materials used in this unit are intended for this use and are installed accordingly. It's just as safe to use as any other plug-in appliance or extension cord you can buy.

Thank you for your comment/question.


2 years ago

Thank you very much. I really needed this for my project. My only problem is that its hard to find some of the materials.


4 years ago on Introduction

I like the plugs you used. I can't seem to find any female plugs that aren't huge.


6 years ago on Introduction

Cool project... The box I have doesn't have a grounding bar. How would I properly ground the box? I'm making a switch box without the outlet that will allow me to switch on/off a pigtailed garbage disposal under the sink. The electrical outlet available to me is not controlled by any wall switches. The faceplate I have is metal and allows for a waterproof seal around the box while still being able to flip the switch on/off through a lever mechanism. This one linked here is non-metallic but I have a metallic version. Should I remove the vinyl squares too?

the switch I'm using has a ground lug as well

2 replies

Reply 6 years ago on Introduction

Hi, if I were you I would buy a combination switch/outlet and wire that up in the device box where your existing outlet is. Hopefully the outlet is the last one on the circuit or on it's own dedicated breaker. Make sure you have good ground first by checking the live and ground holes in the outlet with your voltmeter, it should read somewhere between 110 and 120 volts.
However, if you go the extension cord route, you don't need to ground non-metallic boxes, just make sure that the line ground and the load ground are twisted together with one of the ground wires secured under the green screw in the box.
Please make sure that garbage disposal is properly grounded. If not, your kitchen sink may someday become electricly live and you could get electrocuded if you touch it.


Reply 6 years ago on Introduction

Basically I'm trying to put a switch in line with the live wire in a plastic box. Should I remove the vinyl squares? Can I use a metalic cover or should I switch to plastic.

The disposal has a pigtail connector, black, white and ground. ground on disposal to ground on switch to ground in outlet. Then white neutral on disposal straight through to outlet plug. and lastly the live wire from disposal to terminal of switch then from the other terminal of the switch to the outlet plug. The metal faceplate is a problem though correct?


Nice job. I've been using these for years.

A couple of improvements or options:
1. Use a lighted switch so you know at a glance if it is powered.
2. Use a GFCI plug for extra safety. (which you already stated) I wouldn't use the test button as an on/off. They aren't designed for too many actuations.
3. Make it smaller by using a combination, switch with single outlet. (you can wire the outlet through the switch)
4. Use a higher wattage dimmer switch to control the speed of a small motor driven device like a scroll saw or flexshaft rotary tool (similar to a dremel) Watch the temp of the switch, they can overheat because they aren't really meant to be used that way.
5. Use a rotary timer switch to power your Christmas lights. (Auto off after a couple hours)
6. Use a bigger box and wire a pool pump timer to control your Christmas lights. (quite a bit more money, but the small pre-built ones don't usually handle enough amperage.)


6 years ago on Introduction

Thank you for sharing. One of the byproducts of my urban mining
 is LOTS of electrical cords from lamps, stereos, tv's all kinds of things, the cords themselves are worth money in scrap copper even if the electronic device isn't. I usually just buy a couple of female ends for the longer cords (vacuum cleaners and steam cleaners usually have 10 or more feet of cord) but I'll have to make a couple like this