DIY Portable Switched Power Outlet With Extension Cord

In this Instructable, I’ll be making a safe, robust, portable switched power supply from commonly-available parts. These are very handy to have around the workshop, especially when you need to control tools without an on/off switch, or where the switch is in an inconvenient location. They're also helpful for workbenching, where you need a convenient way to control power to a tool or assembly you're testing.

I made this one specifically to control power to my table-mounted portaband saw, which has a finger trigger for power usually. When table-mounted, it's far easier to clamp the trigger down and control power with a switch.

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• 4” by 4” metal junction box with a raised dimple inside for a grounding screw
• Exposed work cover, with slots for a switch and a duplex receptacle
• Switch (15 amp rated)
• Duplex receptacle/outlet
• 14 gauge power supply cord, with ground
• 18” of green 14 gauge wire
• 6” of colored 14 gauge wire (doesn’t matter what color, just not white)
• Clamp connector and red plastic bushing
• Grounding screw
• Wire nut

Tools:

• Wire strippers
• Screwdriver(s) with #2 Phillips and flathead tips
• Lineman’s pliers
• Electrical tape

To start off, we’ll need to bend off the tabs on the receptacle and the switch. These are used when wall-mounting to keep proper spacing off of drywall, but they get in the way of the exposed work cover we’ll use later. Use the pliers to bend the tabs back and forth until the metal fatigues and snaps off.

Before getting into things, let’s review the wiring diagram. On the left, we have power coming in from the power cord, with the black wire being hot, white being neutral, and green being ground. The hot wire is fed into the switch, and when you flip the switch, power goes to the receptacle. The circuit is completed via the neutral wire attached on the other side of the receptacle.

Note that this concept can be applied to make a double-switched power supply, where one switch controls only one outlet of the duplex receptacle. There are a couple more steps and additional wires needed to make this type, but it’s really no more complicated than what we're building here.

Take the 18” length of green wire and snip it into three six-inch lengths. Strip about 3/4” off one end of each of the wires. Then, using the lineman’s pliers, twist together two of the wires. With those twisted, add in the third wire. Then cap everything off temporarily with the wire nut. Note: don't just jam all the wires into the wire nut and expect it to hold things together - the wires need to be pre-twisted together before applying the wire nut.

Strip 3/4” from the other ends of these wires now. Once done, use the wire strippers to bend the ends into hooks.

Take the grounding screw and screw it part way into the junction box. Then take one of the hooked wire ends, wrap it around the screw, and fasten it down. Note that the wire is wrapped going clockwise around the screw – this stops the hook from opening up when tightening the screw.

Now is time to attach the ground wire to each of the switch and receptacle grounding screws.

Use the lineman’s pliers to pop out one of the 1/2” knockouts on the junction box. Just hammer on it until the knockout bends out, then twist it off with the pliers. The power cord will pass through here.

Pull the power cord out of its packaging and slip the clamp connector over the end of it. With the connector in position, also slide the red bushing between the cord and the opening in the connector, and then tighten the screws on the connector. The bushing helps keep the connector from cutting into the wires. Remove the connector’s nut, pass it through the knockout, and thread the nut back into place. The nut can be tightened down by pushing on one of the knurlings with the tip of the screwdriver.

Next strip the ends of the wire from the power cord and twist the strands of the wire tighter. Remove the wire nut from the bundle of ground wires, and wrap the power cord’s ground around them. Fasten the wire nut back down on the ground wires.

Now to start wiring the switch and receptacle. Start by forming a hook in the white neutral wire from the power cord and wrap this around one of the bright metal screw terminals of the receptacle. Use a screwdriver to tighten the wire down, and also screw in the other terminal to help keep it from shorting out on anything.

Next, take the black hot wire from the power cord and wrap it around one of the terminals on the switch. It doesn’t matter which one. Tighten it down with your screwdriver.

A quick wiring tip: white to bright, black to brass, green to ground is an easy way to remember how to wire an outlet.

Take out the 6” length of colored wire and strip 3/4" off both ends. Using the wire strippers, bend hooks in both ends. Wrap one of the ends around the empty terminal on the switch and fasten it down. Then, take the other end of this wire and attach it to the brass-colored terminal on the receptacle and also fasten it down.

With the switch and receptacle all wired up, wrap both in electrical tape. This helps protect against anything shorting out on the metal junction box or against one another.

Now to start buttoning things up. Remove the exposed work cover from its packaging. The switch is attached to the cover with the two included screws. For the receptacle, there’s a single screw in the center that fastens it down. Also included are two screws with nuts that can go on the top and bottom of the receptacle, but I don’t find these necessary.

Take off the screws from the corners of the junction box. These same screws are reused to attach the cover. Neatly fold the wires into the junction box, and fasten the cover down with the two screws in the corners. The switched power source is now complete!

You now have a portable switched outlet, ready to be used in any number of situations. As stated previously, this concept can be easily modified to use a double-switched outlet, or to use a ground-fault receptacle for outdoor applications, or any number of other types. If you build one of these, be sure to share it in the comments below!

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