GFCI wiring details, back view (C) Daniel FriedmanBackwiring Electrical Receptacles (wall plugs)
Some back-wired electrical devices perform well, but some older ones may be unsafe
     

  • BACK-WIRED ELECTRICAL DEVICES - CONTENTS: how to back wire an electrical rceptacle (outlet) safely & which types of back-wired receptacles are unsafe. Some back-wired devices perform poorly in the field and risk circuit failure, overheating, or fire. Others may be fine. The distinction is described in this article.
  • POST a QUESTION or READ FAQs about how to install and wire electrical outlets or receptacles in buildings.
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Backwired electrical receptacles:

Using the back-wire or push-in type connection points on an electrical receptacle or switch may be just fine, or it may not be reliable nor safe, depending on the age and type of back-wire connector provided.

Here we describe the types of backwire connectors used on electrical receptacles and light switches and we explain the safety and performance questions that may arise.

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Back-Wired Electrical Devices: receptacles & switches

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Receptacle 20A backwired clamp type (C) D FriedmanThis article explains receptacle types, receptacle grounding, connecting wires to the right receptacle terminal screws, electrical wire size, electrical wire color codes, and special receptacles for un-grounded circuits.

Details about how to wire up an electrical receptacle are at CONNECTION DETAILS - where to connect black, white, red, green, ground wires.

Modern back-wired electrical devices like receptacles and light switches use a clamp-type screw and plate that permits very good contact between the electrical connector on the device and the wire - as shown in our photograph at left.

With wires stripped to the proper length, not nicked, and with the screw tightened, these are, in our OPINION, good electrical connections.

Older electrical receptacles and light switches and some lower-cost modern products use a spring-clip type contact that presses the mere edge of a metal spring or clip inside the device against the edge of a wire that is pushed into the device through a hole on the device back.

These devices provide less electrical contact area between the device electrical connector and the wire surface than the clamp type connector, but are code-permitted and may work acceptably provided that the devices are not re-used. That is, in our OPINION, if you remove and reinsert wires in such devices the spring may be weakened and the connection less reliable.

Back wired electrical receptacle (C) Daniel FriedmanStill older receptacles and switches (shown at left, no longer sold in the U.S. or Canada) used a hole diameter on the device back that would accept either No. 12 or No. 14 copper wire to be connected by a push-in back-wired connection method.

Not only did these devices sport a limited electrical contact between the wire and the connector (just the edge of a flat spring in contact with the edge of a round wire), but worse, if a device was back-wired using No. 12 wire and later re-used with smaller diameter No. 14 wire, the contact spring, having been bent open by the No. 12 wire, performed poorly against a No. 14 wire later inserted into the same opening.

In our OPINION these older devices were less reliable, less safe, and should not be used by backwiring. The devices would perform acceptably, however, if the screw connectors on the device side were used to connect the wires.

Reader Question: Is it safe to plug a 10-Amp A/C into an outlet that is back wired?

is it safe to plug in an ac unit that runs 10 amps , into outlet that is backed wired, i had read that you don't like this method, the outlet is on third floor and is on a 15 amp breaker - Johnny B 5/2/12

Reply: Comparing Three Types of Backwired Receptacles: 20-A Clamp Type & 15-ASpring Type & Clamp Type Backwiring Devices

Johnny, that's an interesting question and one I'm scared to answer - by online posting one cannot assure the electrical safety of your building.

Here we will illustrate three different types of electrical receptacles that can be wired from their back-side.

Our photo (left) illustrates a spec-grade 20-Amp, 125V rated electrical receptacle that looks as if it is "back-wired" - in fact while a wire can be wrapped around the terminal screws on this device, the screw is intended to be used to tighten a rectangular brass plate against a square metal nut (silver in color) that makes a very strong and positive connection over a good area of wire surface. This receptacle is marked on its back surface as CU Wire Only - copper only. [Click images to see enlarged details.]

That said, I agree that older, spring-type back-wired electrical connections (shown at below left) are not as reliable as connections made under a screw or clamp, as the total contact area between the back-wire spring edge and the wire surface is minimal.

Nevertheless, on a 15-A circuit using 15-A devices such as receptacles, the circuit and its devices are rated and intended to be able to support the 10-amp load you describe, so long as the sum of all of the items plugged into that electrical circuit don't overload it.

Contractor-grade 15-A spring-type-connector back-wired electrical receptacles (below left) provide a single opening at each of the four terminals (two neutral wires, two hot wires) on the back of the receptacle (red arrow). The yellow arrow points to a release spring that will allow removal of the wire, but we prefer not to re-use this type of back-wired receptacle. Tightening the screw at the main wire terminal (blue arrow) has nothing to do with the spring-clamp that is securing the back-wired terminal wire.

Back wired electrical receptacle (C) Daniel Friedman Back wired electrical receptacle (C) Daniel Friedman

Some newer heavy-duty 15-A back-wired electrical receptacles (above right) o not rely on a simple spring-edge to contact the electrical wire, as we illustrate in our second photo (above right). Rather, when the wire is inserted into a receiving hole on the back of the receptacle (either of the two red arrows).

When the terminal screw is tightened (blue arrow) that actually snugs up a clamp that contacts a much larger surface area of the back-wired wire. That's a more secure connection mechanically. On this receptacle, instead on a single back terminal accepting a single wire, there are a pair of back terminal openings at each of the four terminal screws.

Follow-up:

Thank you for responding, my town home was built in 1999, not sure if that is considered newer or older, lights do dim though when i use 10 amp vacuum . - Johnny B.

Reply:

Backwiring electrical receptacles is a permitted installation and might be found in a 1999 home - but as we show above, there are two different approaches, the second of which is a better quality installation and is in our opinion more reliable.

Reader Question: what's the difference between "line" and "load" terminal screws on electrical receptacles? How do I hook up a quad of four receptacles to an existing circuit?

GFCI wiring details, back view (C) Daniel FriedmanWhat is the difference between the load and line terminal screws on a 15 or a 20 amp receptacle? How do i wire 4 more receptacles to an existing receptacle in a room? - Anon

Reply: how to wire line and load terminals on receptacles (outlets)

Anon: the line and load electrical wire connections are important to get right on certain electrical devices such as GFCIs and AFCIs. Our photograph (left) illustrates the line and load markings on the back of a GFCI electrical receptacle.

Looking at the side or back of the molded case of this and other electrical devices such as AFCIs, you will see that one pair of terminals will be marked "line" and the other "load".

Which wires connect to the "Line" terminals:

The Line terminals (green arrows in photo at left) on an electrical receptacle are for the incoming hot wire - the terminal marked LINE is connected to the incoming power source or the "hot" wire (typically black or red in insulation color) that connects to the brass colored screw (marked "Black" or "Noir) at the lower left " in our photo.

And the incoming neutral (white) wire from the electrical panel connects to the "Line" and "White" or "Blanc" terminal marked at the lower right in our photo

Which wires connect to the "Load" terminals"

The Load terminals (red arrows near the top of our photo at left) on an electrical receptacle are for the outgoing wires. These wires feed electrical receptacles that are located "downstream"(farther from the electrical panel) from the device. The outgoing hot or black wire (red arrow, above left in our photo) connects to the terminal marked "Load" or "Charge" and "Black" or "Noir". The outgoing white, neutral wire, connects to the terminal marked "Load" or "Charge" and "White" or "Blanc" in our photograph.

Re-stating, terminals marked LOAD on a GFCI or AFCI are intended to be used to feed other devices (such as receptacle) that are wired "downstream" from the one being worked-on. In a string of electrical receptacles wired in series, incoming electrical power flows in to the first GFCI/AFCI receptacle and is connected to the LINE terminal. The LOAD terminals of that device are connected to hot and neutral wires that subsequently are connected to the next electrical receptacle in the series.

To hook up a quad of electrical receptacles you'll need a larger junction box. And often we wire two separate electrical circuits to the box, placing one pair of receptacles on one circuit and the other on the second circuit - that approach allows us to plug more devices into the wall at that location with less chance of overloading a single electrical circuit in the building.

Watch out: while a conventional receptacle may work with the line and load terminals reversed, a GFCI or AFCI will be unsafe if wired with that mistake, and those devices will not work properly nor test properly in all circumstances. For example, if you connect the incoming "hot" wire and neutral wire to the "load" terminals on a GFCI, and if you connect wires leading to downstream electrical receptacles to the "line" terminals (these are the incorrect connections), then pushing the test button on the GFCI will not activate that device's internal trip mechanism.

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.

Reply:

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.

  1. If the incoming ground wire from the feed circuit was left long enough, it can be run continuously, connected to a grounding screw that connects the wire to the metal junction box (skip this step if plastic junction boxes are in use), on to the ground screw terminal at each electrical receptacle, and ending with a ground clamp crimp connector that ties the incoming ground to the ground wire of the outgoing wire that continues to the next junction box.
  2. If the incoming ground wire is not long enough to run as above, then an additional length of ground wire is pigtailed to the incoming ground and makes the other connections I've described above.

Electrical receptacle mounting strap and screw are not a ground (C) D FriedmanIn sum, all of the grounds are tied together in the box: the incoming ground, outgoing ground, and ground wires to each of the 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.

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.

Question: how to wire up a pair of receptacles in one electrical box

Quad plex electrical receptacle wiring (C) Daniel FriedmanI would like to wire 2 single plug ins to one live wire..how do i do that? - Channing

Reply:

Channing, re Hooking up a Pair of Receptacles in One Electrical Box:

If your two plug ins (two electrical receptacles) are located in the same electrical box (we call this a "quad" electrical receptacle installation since each individual receptacle provides connections for two wall plugs), you'll want to wire the hot and neutral to one pair of screws on the first receptacle, and use short black and white jumper wires to connect the the proper terminals on the first receptacle to the second one in the same box.

That's a perfectly acceptable use of the second pair of screw terminals you see on the receptacles.

The ground wire can be continuous, tying the two ground screws on the receptacles together and onwards to the circuit ground.

However a better practice when wiring up a quad-plex of electrical receptacles is to place left and right or upper and lower receptacles on separate electrical circuits - thus reducing the chances of overloading the circuit when many things are connected simultaneously. There are two approaches: you can wire the left and right duplex receptacles each to different individual electrical circuits, or you can wire the upper and lower half of the pair of duplex receptacles to different electrical circuits.

Wiring a Split Receptacle to Two Different Electrical Circuits

Electrical receptacle split receptacle wiring (C) Daniel FriedmanIf you choose to wire the upper and lower duplex receptacle openings to different circuits, we call this the "split receptacle" wiring method, because we are splitting the individual duplex receptacle upper and lower connectors onto two different circuits.

Our photo (left) shows an electrical receptacle that is being wired to a single circuit. The white neutral wire is connected to the silver screw (left side of our photo).

If we were wiring this electrical "outlet" as a split receptacle, we'd want to feed the upper and lower halves of the device from two different electrical circuits.

To do so we'd have to break away the "breakaway" connecting tab pointed to by our orange arrow.

Daisy Chaining Receptacles in Separate Electrical Boxes

If your two receptacles are in different locations and thus in different electrical boxes, your circuit that wires the second or "downstream" receptacle can be powered by those same extra terminal screws on the first or "upstream" receptacle. You'll need to run a wire from the first receptacle through the wall into the second electrical box of course.

Wiring Electrical Receptacles on a Single Circuit In Parallel

In some jurisdictions electricians to not "daisy chain" receptacles in the same box together by using the second pair of screws on each one. Rather the circuit enters the box and using twist-on connectors, short pig-tail wires are connected to each receptacle at the proper screws. This approach requires a larger electrical box as it will contain more connections, connectors, and so needs more room.

 

 

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