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How to Wire a Simple 120v Electrical Circuit

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How to Wire a Simple 120v Electrical Circuit

Hiring an electrician is often the best way to go when 120 volt circuits are concerned. But if you are up to it, you might be able to save a lot of money by doing some electrical work yourself. This article covers a simple 15 amp circuit involving one 120 volt outlet.

Steps


Turn off all electricity feeding any panel you are going to be working in. And, familiarize yourself with all of the tips in the related wikiHow on "How to Master Do It Yourself Electrical Safety" (See the link to the right of your screen.)
Choosing and installing electrical boxes, conduit, etc. are beyond the scope of this article. So, before proceeding with the wiring, you will need to get the receptacle box and the path for the wires between the receptacle box and the electrical panel installed and prepared.

 
Put a couple of pieces of electrical tape over the end of your wires, so the copper is not exposed. This way, if your wire touches a exposed live conductor while feeding it through, it won't conduct the current back to you.

 
If you have installed conduit and the run is very short, you may be able to just push the wire from the outlet box back through to the electric panel. If the run is not short, you may need to push a "fish tape" through to hook onto the wire and pull it through. Or, if you don't have conduit, you will have to "fish" ("fish" and "snake" are two words that mean the same thing) the cable or remove wallboard and possibly drill 5/8 inch or larger holes through the wall studs to feed the wire through. In any event, you have to get the wire run between the electric panel and the outlet box in a way that it is not exposed and the insulating "jacket" is not cut.


Cut the wire to length so that 20cm (8") sticks out of the outlet box, and about 80cm (30") sticks out at the electrical panel.


Cut about 15cm (6") of the (usually yellow or gray) outer jacket away from the wire, being careful to not damage the inner black or white jackets. This usually leaves one bare copper or green wire (the ground wire), one black wire (the hot wire) and one white wire (the neutral wire).

 
Assuming you ran #14 gauge wire (this is the MINIMUM size), Find the larger "12 gauge" jaws on your wire strippers. Use them to strip about 1.5 cm (5/8") of the jacket away from the end of both the black and white wires. If you can't strip the jacket, use the "14 gauge" jaws. Using the 12 gauge jaws of the tool significantly decreases the chance of nicking the wire. When using the 14 gauge jaws, hold the tool at a right angle to the wire, otherwise you will damage the wire. Also strip the end of the ground wire if it is insulated. If you cut too deep, don't worry... Cut the end off and try again. You have 3 or 4 tries before the wires will start to get too short to work with. It is very important to NOT nick the wire.


If the outlet is only going to have 3 wires connected to it, Use the needle nose pliers to form a small hook the exposed copper ends of all the wires. Otherwise, cut 8" pieces of black, white and bare / green wires from the unused portion of the roll to be used as "pigtails". Carefully strip both ends of the pigtails as outlined above. Gather all of the "hot" wires (blank or red usually) and the 8" black pigtail. Twist them together and spin a properly sized wire nut securely over the top. No exposed copper should be seen extending from the wirenut. Fold the group towards the back of the box, with the pigtail sticking out to the front of the box. Use the needle nose pliers to form a small hook the exposed copper end of pigtail. This lone black wire represents the bundle of blacks, and will be easier with which to work. Repeat this procedure for the remaining wires. If you have a metal box, you'll need to cut an extra bare / green wire pigtail to ground the box.


Look at the outlet. On the side of the outlet, you will see screws. The screws will be darker on one side than the other... Usually, brass for the dark side, and silver for the lighter side. On the back of the outlet, you will see 2 or 4 sets of small round holes near the screws. These are the "back wire" points.
Wrap the hook of the wires the screw terminals of the outlet. It provides a significantly superior connection than back wiring, and no electrician uses them on his own house because of it. If you insist on back wiring, insert the tip of the black wire into one of the holes nearest the dark screws and push it in as far as it will go. You may need to use the needle nose pliers to push the wire in, as these can be really stiff sometimes. The wire should go nearly the full 1.5 cm (5/8") in. Repeat this with the white wire into a hole near the lighter colored screws.
On one end of the outlet will be a green screw. Put the hook you made in the ground wire clockwise around the green screw. Then tighten the screw until it is secure... This should be tight.

 
That completes wiring of the outlet end of the circuit... gently push all the wires back into the electrical box, screw the outlet into place, and put the cover on it.

 
Go to the electric panel end of the circuit. Double-check that the power is as turned off, BUT NEVER TRUST THAT IT IS OFF. Treat all exposed wires and conductive metal as though it is live. Put the rubber mat down and stand on it while you do your work, and bend the wires out away from the panel while preparing them, so that your hands are not working close to potentially live circuits.

 
Locate the grounding post. This is a long bar of screw clamps that will have existing exposed copper and green (ground) wires clamped to it. Often, it will also have white wires clamped to it.

 
Cut the ground wire to length so that it comfortably reaches the grounding post after following a path out of the way of other wires, typically following right-angles across the bottom of the panel and up to the grounding post. Don't cut it too short, but don't leave too much slack either. If the ground wire has a green jacket, strip 1.5cm (5/8") of the jacket from the end of the wire.


Find an unused terminal on this grounding bar, unscrew it part way, insert the ground wire, and then tighten the screw back down onto the exposed copper until the wire is secure.
Locate the neutral bar if there is one. This is similar to the grounding post, except that it will have only white wires hooked into it. In many cases, the neutral bar and ground bar is the same. If this is the case, both the ground wire and the white neutral wire may be terminated to the same grounding bar.


Cut the white neutral wire to length, then strip 1.5cm (5/8") of the jacket off and bind it to the neutral binding post the same way as you did for the ground wire. Place only one wire per terminal.

 
Locate the open slot in the electrical panel that you want to install this circuit into. Note that there is a conductive bar that sticks out on one side, and a plastic tab on the other.
Being careful to not touch anything conductive, determine the length of wire needed to reach this slot easily, also following a path around the outside of the panel. Cut the wire to length.
Locate the single binding screw on the new circuit breaker. Don't put the breaker in place yet, but take a look at how there is a slot for the tab in the panel to fit into, and there is another slot where the conductive bar will fit.

 
Strip 1.5cm (5/8") of the end of the black wire, insert it into the breaker, and bind it tightly to the breaker.
Make sure that your new breaker is switched off.
Standing on the rubber mat, place one hand at your side or behind your back... This is not a tasteless joke, but is actually a safety measure. Working with two hands is dangerous because if you ever touch anything that is hot, current can run in one arm, through your heart, and back out the other arm. One hand is all you need, so keep the other out of the way.
Using your remaining hand, slide the slot in the breaker over the tab in the electrical panel. Then firmly push the other end of the breaker in over the electrical contact until it is seated in line with the other breakers.

 
Locate the place on the panel cover where this new breaker needs to be exposed. There is very likely a metal tab that needs to be broken out of the panel so the new breaker can stick out from it. Break out this metal tab and put the cover back on the panel.


Turn the main breaker back on, and check that electrical devices still function. If any breaker immediately trips, it probably indicates that you created a short circuit. In this case, you will need to either shut all the power off and retrace your steps to find it, or call in an electrician.
Turn the new circuit on and make sure it doesn't immediately trip, the same as in the previous step.

 
Plug a lamp into your new circuit to test it. Odds are that it will now work just as it should. Smile because you just saved yourself $300 or more!

Tips


This same procedure can be used to create a 20 amp circuit if (and only if) you substitute a 20 amp breaker, 12 gauge wire, and a 20 amp outlet in combination. Do not substitute one of these parts without substituting ALL of them.
Apply for a permit for this work in your town's building or code enforcement office.
Have your work inspected. That $300 you saved is peanuts if you lose all your possessions or a loved one to an electrical fire.


Warnings


If you aren't fully aware of the safety requirements of electrical work, don't do this. Mistakes are literally deadly in this kind of work.
Inside an electrical panel, EVEN WHEN THE MAIN BREAKER IS OFF, deadly high voltage currents can be exposed. This is true by design in many cases, so DO NOT assume you are safe just because you have a new well maintained panel.
If you see red or black wires clamped to the grounding post or to the neutral binding post, DO NOT PROCEED. This indicates non-standard and potentially dangerous existing wiring. It is best to close the panel back up and hire a professional electrician to advise you on it or do the work.
Do not use 20 amp breakers with #14 gauge or smaller wire. This creates a fire hazard as #14 is rated for 15 amps max.
Do not use 15 amp breakers with 20 amp outlets. 20 Amp outlets look different than 15 amp outlets, and use of a 20 amp outlet indicates to future users that there are 20 amps of power available. This will not be true with a 15 amp breaker (this applies in commercial and industrial buildings only as residential buildings do not need 20 amp outlets even if on 20 amp circuits).


Things You'll Need


A 15 Amp circuit breaker
14 gauge "2-wire with ground" wire of sufficient length to reach where you want the outlet
A 15 amp rated electrical outlet
An installed outlet box, ready for the outlet and wire
A path, whether in conduit or other approved method for the wire to run from the box back to an electrical panel
One open slot in the electrical panel for the new circuit to be installed
Wire strippers
Needle nose pliers
For long runs, electrical "fish-tape" may be required
Rubber soled shoes, ideally with a rubber floor mat.