Adding an outlet to an existing wall is a difficult do-it-yourself endeavor. There’s a risk of burning down your own home or electrocuting yourself if you make the slightest mistake. If you don’t have adequate background in handling electrical wiring systems, it is highly recommended that you hire a professional electrician. In any case here are some guidelines that will give you an idea of what the job entails.
1. Turn off the electrical power of the whole house.
When dealing with something as complex and dangerous as your home’s electrical system, the necessary first step is always to shut down the power.
2. Find the correct spot to place your new outlet.
You already know which wall in which room you want to add the new electrical outlet to, but the exact spot cannot be arbitrarily chosen, as there are internal structures in the wall that you need to avoid. Wall studs are one of them; others could be plumbing or ventilation shafts. You can tap on the wall lightly with a hammer to find a spot that has an empty cavity behind it. You can also poke a small hole and insert hanger wire into it to feel around the inside just to make sure no plumbing, electrical or mechanical structures exist in that same wall space.
3. Mark the correct spot.
Measure how high from the floor the other outlets in your home are installed. You probably need to take out the cover plate on one of them to accurately measure the height at which the hole for the outlet was made. While you’re at it you might as well measure the dimensions of the hole so you already know how big a cavity you’re going to make.
4. Find out where to tap electrical power.
You cannot tap from the additional wires that go into pre-existing electrical boxes in the ceiling or the basement. These extra wires contain constant power. The only safe wires to tap are those that already lead to other existing outlets so it’s crucial that you trace the right pair of wires. Make sure once more that power for the whole house is shut down and then go ahead and cut the wires. Connect these ends into a new electrical box and mount this in the floor or ceiling structure
5. Drill holes along the path of the new wires.
You’ll be connecting the additional outlet to the new electrical box with a set of wires that will be run inside the wall, floor, or ceiling. It’s necessary then to drill holes where these wires will be passing through. Make sure the drill bit is larger in diameter than the wire and at least 4 inches long, as you’ll be making holes through thick structures. Also be certain that you’re leading towards the spot you’ve chosen earlier.
6. Prepare the wall cavity for installation.
Going back to the spot on the wall you marked out earlier; cut out the wall in the exact dimensions as the outlet box you’re going to use to house the new outlet. A good utility knife will do for sheetrocked walls, but for plastered walls you may need to use a hole-saw. Lay down the new set of wires that will connect the outlet and the electrical box. One end connects to the electrical box and the other will be inserted into the outlet box. Connecting the new wires to the pre-existing cut ones is a matter of matching wire colors, as these wires are usually color-coded. Make sure there are no loose wires and that wire nuts are screwed down tightly. At the wall cavity, you can securely mount the outlet box using the fasteners or clips that come with it. If you cut out the wall correctly, the outlet box shouldn’t wiggle.
7. Put in the outlet receptacle.
With the outlet box and wires in place, you can now put in the outlet receptacles. Connect and screw down the wire ends into their proper terminals on the receptacle. You might want to consider putting in a third wire for grounding. You should also wrap electrical tape on the inside-facing part of the receptacle for added protection. Afterwards, you can mount the outlet’s cover plate.
Double check the connections before you turn the power back on and test the new outlet. Use a simple appliance with small electrical requirements like a lamp that uses a low wattage light bulb for testing. If you don’t see any sparks, smell any smoke and the appliance works, then you probably did it correctly.