How to splice or extend wires as needed when wiring up an electrical receptacle (wall plug or outlet).
When wiring electrical circuits in a building it may be necessary to join or extend wires using a mechanical splice.
Here we discuss splices commonly made when wiring electrical receptacles (wall plugs or outlets) and switches.
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That's because the push-in terminals on some electrical outlets and switches are less reliable than the side screw terminals.
Studies have shown (Aronstein) that back-wired electrical receptacles whose wires are simply pushed into a round hole at the back of the receptacle have a very small contact area between the receptacle and the wire (just the very edge of a flat spring), and that this contact can be damaged, especially if the receptacle is re-used.
Watch out: On older versions of push-in terminals the hole for the wire would admit a #14 or a larger #12 wire. If an outlet was first wired with a #12 wire (which bends the contact spring farther open) and later re-wired to a #14 wire, the connection was particularly unreliable.
Some if not all newer electrical outlets with push-in terminals have been modified to use only the smaller #14 sized wire opening to prevent this failure. But we still prefer the increased contact area and increased contact security that comes from being able to tighten a screw.
A screw-terminal (upper left in the sketch) is a more reliable connection for wiring at an electrical outlet. Some newer electrical outlets have a back-wire push-in type terminal which uses a screw to securely pinch the wire in the receptacle - these are fine. The splice at lower left in the sketch depicts using a twist-on connector - the right way to make a wire splice inside of an electrical junction box.
See more electrical wiring splice instruction details at ELECTRICAL SPLICES, HOW TO MAKE
Reader Question: I don't have enough wire to lower receptacles on the wall
I recently moved into a 3 1/4 story home, and I have a basement that I am trying to finish with drywall. The room is down to the studs and the electrical receptacles are about 4' up the wall.
The Romex wiring is stapled, and there isn't enough wire to lower them. It is way to much work for me to replace all of the downstairs wiring right to the breaker box, so I'm wondering if it is possible to add onto the existing wires and attach wire screws or marrets within the walls before I start adding drywall, or whether I should add some kind of junction box to contain the marreted wires in between.
My building code stipulations would differ in some cases because I live in Canada, but I just want to do the job right, and I do not want to take the chance of having any fire hazards, as I also have small children. - Dave 2/10/12
Dave,. you are correct to be careful about moving outlets or any other device when the existing wires are too short. The temptation is to just splice on an extension and bury that in the wall or ceiling: an illegal, improper, unsafe as well as really aggravating approach.
The proper approach is to add a junction box at each splice - we never splice 120/240V wires without including them in a box. You can reduce the wiring work a little by using plastic boxes instead of steel - avoiding having to also connect the box to the ground wire.
The proper approach also means that you don't then bury any of these splice-boxes in the walls either. Each box has to be brought to the surface and covered.
The result is a lot of work and expense and an ugly wall with an extra junction box and blind cover all along the wall over each of the now moved or lowered electrical receptacles.
Frankly I figure that especially as you've already got the wall open to the studs, if there are more than one or two receptacles to be moved you'll probably find it is actually much less total work to re-wire the entire circuit, allowing proper lengths of wires for each box. You might carefully remove and re-route the existing wire lower in the wall or you might buy all new electrical wire - depending on the age and condition of the existing materials.
Watch out: when removing wire that appears to be in good condition, if you nick the insulation you've created a new hazard.
Reader Question: can I connect a pigtail from multiple hot, neutral, or ground wires over to a receptacle
I have 2 receptacles that are both side and back wired, 3 hot and 3 neutral wires. I eliminated one receptacle (capping the 3 wires together) but want to keep the other. Is it safe to just run a pigtail from the 3 wires to the receptacle? - Greg
When wiring multiple boxes in series, how do you connect both incoming and outgoing ground wires to the back of the receptacle? With 12 ga. wire, only one wire will fit under the green screw (and not very tightly, at that - there's no washer or clamp.) - Bob M.
Yes, Greg, that's a common practice. Be sure that your junction box is big enough to contain all of the wires and twist-on connectors.
Bob, similar to Greg's question, I see two approaches to hooking up the ground wire in junction boxes and at electrical receptacles.
Watch out: while the electrical receptacle ground may also be electrically connected to the metal strap that mounts the receptacle to the junction box (photo at left), and while the junction box may be metal, do not rely on the receptacle mounting screws and receptacle strap-to-box contact to serve as the grounding connection.
It's easy for the receptacle mounting screws to be deliberately left loose or to work loose - making that ground connection unreliable. Use a ground wire.
Reader Question: How do you connect 14-3 to 14-2 to a junction box - Moe.
Moe, twist on connectors are used to connect the incoming and outgoing hot, neutral, and ground wires, and a single pigtail length in that same twist-on connector can connect the ground to the local junction box.
Watch out: when mixing 14-3 and 14-2 wires on an electrical circuit.
If the 14-3 wires are the hot wires entering the box, and if only 14-2 is leaving the junction box, cap off the unused (typically the red) hot lead.
Do not just bond it together with the outgoing hot wire in the 14-2 group. Making that mistake would short two hot leads together, would be improper, unsafe, and a fire or shock risk.
Details about how to wire up an electrical receptacle are at ELECTRICAL RECEPTACLE CONNECTION DETAILS - where to connect black, white, red, green, ground wires .
This article series describes how to choose, locate, and wire an electrical receptacle in a home. Electrical receptacles (also called electrical outlets or "plugs" or "sockets") are simple devices that are easy to install, but there are details to get right if you want to be safe.
putting in more than outlet on along a 12ft wall - Mike Tucker
Mike, if your comment is a question of how to put in more than one outlet along a 12 foot wall, yes it's perfectly permitted to exceed the minimum number of receptacles along a wall.
The wiring system is unchanged except that in some cases I recommend installing two different circuits and alternating which outlet is served by which circuit. That avoids overloading one circuit if you are plugging in lots of devices in one area.
I have an existing outlet being used for lamps I wanna run one more outlet shares from the hot on is it okay? - Phantum 113 8/1/12
Usually, yes provided all safe and proper wiring code procedures are followed.
If the circuit is overloaded already, no.
If the circuit is knob and tube wiring, no - we don't extend knob and tube.
I’m attempting to wire two separate receptacles from one (line) wire, not in-line one after the other but effectively as a “Y” from a junction box with two load lines out (one to a north wall receptacle and the other to a south wall receptacle in my barn).
Using screw-on connectors, I connected the three black wires together; the three white wires together; and the three green wires to a pigtail screwed into the junction box. One receptacle works fine, but plugging anything into the other receptacle trips the circuit breaker. If this is not the correct wiring configuration within the junction box, what is the solution? - Robert 8/9/12
I agree that you've got a miswired connection and it sounds like a short somewhere, but no way can nor should someone risk killing you by pretending we can see what you did. There are plenty of possible snafus, such as overtightening a wire clamp that cuts into and shorts a wire.
Turns out the over tightened wire clamp cutting into a wire was the problem.
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I would like to wire in an outlet on the same wall where there is currently a light switch. Can I run wires from the light switch to power the outlet?The light switch is a 2 way switch. thank you. - Marv Walker 7/10/12
Well yes, maybe, sort-of.
Because a light switch is indeed switching a hot wire to the light, you've got power at the switch location. But depending on how the building is wired, you may not have an acceptable neutral wire, and in some still older circuits you may not have a safe ground wire.
Provided that you know how to work on electrical wiring without getting killed by electrocution, you (or your electrician) will open the switch box, carefully pull the switch assembly out enough to inspect for additional wires that may be present, and then use a VOM or DMM or even a simple neon tester to determine what wires are present.
To add a receptacle you need a proper hot, neutral and ground wire.
Watch out: if the "hot" wire in your light switch is on a 3-way circuit you may not always have power at your add-on receptacle.
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