Comparing grounded and un-grounded electrical receptacles (C) D Friedman 2-Wire (no ground) Electrical Outlet Installation Wiring Details
How to wire an electrical plug outlet or wall plug when no ground wire is present
     


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How to wire an electrical receptacle ("outlet" or "wall plug") when there are just two wires (hot and neutral) but no ground wire.

This article explains that when there is no safe grounding conductor or "ground wire" at an electrical receptacle location you need to choose the proper receptacle type and make the proper wire connections for safety.

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.

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How to Hook up an Electrical Receptacle (wall outlet) on a Two-Wire Electrical Circuit

Skecth of number of conductors in types of electrical circuits (C) Carson Dunlop Associates

Step 1: Recognize that the electrical circuit has just two wires and no electrical grounding conductor

In Carson Dunlop Associates' sketch at left the wire circuits shown at upper right and lower right are both two-wire electrical circuits where no ground wire is present. At right in the photo is the type of electrical receptacle to use on two-wire (no ground) circuits.

[Click to enlarge any image]

If no ground wire or ground path is provided, it is improper and unsafe to install a grounding (3-prong) electrical receptacle on that circuit.

Watch out: as you see in the two illustrations at the left of our sketch, a circuit with a ground wire will present a bare or green-insulated wire and there will be three wires (or more) present. The flexible metallic conduit exterior of BX cable, for example, is not a safe, usable pathway for electrical grounding.

We use the proper term electrical receptacle to describe the "wall plug" or "wall outlet" into which you will insert a two-prong or three prong plug to connect an appliance, lamp, etc. Technically in the electrical code, an "outlet" is any place in where you provide a junction box and electrical wires to which something can be connected: a light fixture or an electrical receptacle, for example.

Before doing any work on the switch, the power source must be turned off by setting a circuit breaker to OFF or removing a fuse.
See SAFETY for ELECTRICAL INSPECTORS

Step 2: buy the right type of electrical receptacle

Comparing grounded and un-grounded electrical receptacles (C) D FriedmanOur photo (left) shows a conventional grounded three-prong electrical receptacle - the round hole is the ground connection - at the left end of the picture closest to my thumb.

At right in the photo is an ungrounded electrical receptacle. This is the right device to install if no ground is present on the electrical circuit.

You don't want to "fool" a building occupant into thinking that a ground is present when there is not one, so you don't install a receptacle that has that third ground opening in its face.

Some older two-wire circuits which are covered with a flexible metal jacket ("BX" or "armored cable" wire) may provide a ground path by means of the cable jacket itself.

We don't rely on it, and in event of certain short circuits it's unsafe: the exposed metal sheathing of the wire becomes live, risking a shock.

Step 3: Wire the un-grounded electrical receptacle

So where do the wires go: to which screws on the electrical receptacle (shown just above) do we connect the black wire, white wire when there is no ground wire?

On a conventional 120-volt "two pronged" electrical outlet that accepts grounded plugs (two prongs plus the rounded center ground connector prong), your circuit will have three wires:

  • The white "neutral" wire - this wire is connected to the silver screw on the electrical receptacle, often labeled "neutral" . You can see our white neutral wire connected to a silver screw on the receptacle in our photo, below-left.
  • The black "hot" wire - this wire is fed from the circuit breaker to deliver power to the receptacle, and it connects to the brass or bronze-colored screw on the receptacle, often labeled "hot" or "live".

    You will see the hot black wire connected to the bronze or darker-colored screw on the receptacle shown at below right. The receptacle we used for these photos happens to be a 20-A rated device that permits the wire to be inserted straight into a clamp that is tightened against the wire by the screw.

    Also see BACKWIRED ELECTRICAL RECEPTACLES.
Wire strip gauge (C) D Friedman Electrical Outlet wire connections (C) D Friedman
  • The missing ground wire - since a two wire circuit has no ground wire, you should have chosen an electrical receptacle that does not include an opening for the ground prong on a wall plug. So the receptacle will also have no ground screw.

    if you had a ground wire you'd use a grounding receptacle and the ground wire connects to the green ground screw usually found on the bottom of the electrical receptacle (photo at left). You can also see our ground wire connected at the left side of our previous photo, above-left.

Color coding of wires to properly connect an electrical outlet (C) Carson Dunlop Associates

The illustration at left shows the typical wiring of an electrical outlet or "receptacle", courtesy of Carson Dunlop Associates.

But the typical wiring instructions for receptacles include a ground wire that may not be present on your circuit - as we explained just above.

Keep in mind that while a two-wire circuit may be permitted and "legal" in some jurisdictions it is not as safe as an electrical circuit (and receptacle) that has a grounding conductor.

Let's at least not make the un-grounded and two-wire circuit / electrical outlet even more dangerous by installing the wrong receptacle type. Installing a receptacle that includes a third opening for the wall plug's ground connector is dangerous if the circuit is not really grounded. Such as "false ground" means a false sense of safety that is not present.

Watch out: Electrical components in a building can easily cause an electrical shock, burn, or even death.

Click any image to see an enlarged, detailed view of electrical wiring details for "plugs" or electrical receptacles.

Step 4 - Mount the Electrical Receptacle in the Box & Install the Cover Plate

The electrical receptacle must be properly screwed to or mounted in the junction box, and the extra length connecting wires carefully pushed back into the junction box so as to avoid crimping, damage, etc.

An electrical receptacle cover plate must be installed over the finished receptacle. We like plastic cover plates better than metal as they reduce the chances of a cover plate becoming electrically "live" and thus unsafe.

Avoid These Unsafe Practices When Wiring a 2-Wire (no-ground) Receptacle Circuit

  • Do not use a 3-wire type grounded electrical receptacle on a 2-wire ungrounded circuit
  • Do not reverse polarity of the hot and neutral wires (discussed just below)
  • Do not extend or add circuits, wires, or devices to an existing two-wire knob and tube electrical circuit.
  • Watch out: while it is "legal" to add an electrical receptacle to an existing 2-wire circuit such as that shown at top right in our sketch above, it is not permitted to extend a knob-and-tube circuit (bottom right in the sketch) to add additional receptacles (or anything else) in most jurisdictions. You can replace an existing damaged 2-wire receptacle in either circuit type but you should not extend or add receptacles and wires to an existing knob and tube circuit.
Reversed polarity on an electrical outlet (C) Carson Dunlop Associates

The hot and neutral wires must be connected to the proper terminals on the electrical receptacle. The "hot" or "live" black wire (or red wire) is connected to the brass-colored screw terminal on the electrical receptacle, and the "neutral" white wire is connected to the silver-colored screw terminal on the electrical receptacle.

Carson Dunlop Associates' sketch points out that the white wire, i.e. the neutral wire, will be connected through the receptacle's internal parts to the wide slot on the receptacle face in order to assure that the neutral wire side of an appliance being plugged-in there is properly connected.

Watch out: Reversed polarity on an electrical outlet is dangerous. If you accidentally reverse these wires the device you plug in to the receptacle may "work" but it is unsafe and risks a short circuit, shock, or fire.

Some appliances and some electronic equipment may be damaged if left connected to a reversed-polarity electrical circuit.

  • Do NOT connect circuit wires to the wrong terminals on the receptacle. Readers have proposed jumping the neutral to ground, for example. Don't do that - it's unsafe and illega.

Can I Install a GFCI or AFCI Receptacle on a 2-Wire Electrical Circuit?

AFCI device image from the US CPSCGenerally, if installed on a 2-wire circuit that has no electrical ground conductor, a GFCI electrical receptacle will protect against a hot to neutral short or a hot to ground short at the receptacle but its internal test circuit cannot be used - that is, you can't easily test to know know that the receptacle is working.

Ground fault protection - GFCI's: The NEC also requires that only special ground fault circuit interrupter (GFCI) protected outlets can be installed in certain hazardous locations like kitchens, baths, garages, outdoors. A GFCI-protected electrical receptacle includes circuitry that turns the electric power off at the outlet quickly should a ground-fault (electricity flowing to earth, such as through your hand and down a water pipe) be detected. [4]

Arc fault protection - AFCI's: Beginning in 2002 the NEC also required arc fault protection for electrical outlets for bedrooms. [4]

AFCI's are similar to GFCI's discussed above, but they include an additional level of protection against fire by detecting small electrical arcing at a connection - a condition that can lead to overheating and fire.

As you can see from this US CPSC photo, you can add Arc fault protection to a home circuit by installing a special circuit breaker in the electrical panel.

By this means you can provide arc fault protection and thus improved fire safety for all electrical outlets on the circuit - for example in the building's bedrooms.

See GFCI PROTECTION,Testing GFCIs AFCIs

and AFCIs ARC FAULT CIRCUIT INTERRUPTERS for details about these devices.

Other Proposals for Adding a Ground to a 2-Wire Electrical Circuit

Reader Question:

I was reading your sections on grounding on older home as I am currently in the process of having several two-prong outlets upgraded. In my research, several people suggested it would be possible to ground to the box using a grounding screw.

I didn't go that route but was looking to see what your site had to say about the practice. I was disappointed to find out it wasn't even mentioned. Is there anything you can say, is it a safe practice? - Thanks. K.B. 8/5/13

Reply:

Thanks so much for the question - in the article above and elsewhere I have mentioned the problem of the missing ground wire on a two-wire circuit and also the problem of unreliable ground connections through the receptacle mounting strap screw - but your question helps me see that I must not have made the point clear and easy enough to find.

When you are replacing electrical receptacles ("outlets") in an existing two-wire (hot, neutral, no ground) circuit that is in good physical condition, the only recommended and code-approved solution (short of re-wiring) that I have found is to install new two-slot (no ground prong opening) electrical receptacles in the box. [I add that if the existing two-wire circuit is a knob-and-tube installation, it is also forbidden to extend or add devices (such as more electrical receptacle outlets or lighting outlets) to that circuit.]

I take it from your message that you already understand the danger of just placing a 3-prong receptacle into an ungrounded box, offering a "faux" ground that would be unsafe.

Why We Don't Just Connect the 3-Prong Receptacle Ground Screw to the Metal Junction Box

In other words, if the circuit wiring into the junction boxes in which you ask about converting from 2-prong to 3-prong receptacles does not include a ground wire, do not install 3-prong outlets and DO NOT rely on just grounding the box to a new 3-prong receptacle's ground screw.

Indeed, mechanically you can sometimes create a detectable ground via such a connection even when there is no ground wire if the box is metal and the incoming wiring is metal-clad BX cable. But the ground pathway back to the panel in that case is unsafe and unreliable for sat least these reasons:

1. Hot wire short: the exterior metal BX cable becomes electrically live in the event of a short circuit - a condition that could shock anyone happening to touch that cable exterior anywhere along its pathway, and a condition that in some cases could even start a building fire

2. Neutral wire short: similarly unsafe but more subtle is a short between the neutral wire and ground anywhere in the circuit. In this case the circuit appears to continue to "work" properly, in that lights light or a device is powered when plugged-in; but the BX exterior sheathing will be carrying the return circuit all of the time that the circuit is in use - potentially shocking someone, and again unreliable as I explain in the next point.

Working on an older home in which someone had done this I encountered exactly this situation - it's not just "theory". Turning off power to a circuit on which I was working, I tested to see that the hot wire was "dead" before touching anything. My helper, working in the same room, plugged in our shop vac to begin some cleanup, connecting the shop vack to a nearby receptacle that had a different hot wire entering it.

The box and BX cable I was working on became "live" (and shocking) when she turned on the vacuum cleaner! The BX cables from several circuits had some metal contact points in common and the neutral circuit was flowing through the BX not through the proper neutral wire (or part of the current was thus flowing).

3. Even if you didn't care about shocking someone or starting a fire, the "apparent ground" path in this case is unreliable because it passes through a great may often loose connections (metal clips that connect each segment of BX sheathing to each electrical box) - connectors that are not designed for nor intended for secure electrical contact to serve as a grounding conductor.

Adding individual, properly-wired new grounding conductors, electrodes, etc. to an existing 2-wire circuit?

If on the other hand, you are considering providing anew, separate local grounding conductor and local grounding electrode to which you connect a metal electrical box, other than a ground wire that passes all the way back to the main panel, that approach might be technically possible.

We need to research the code details further about inconsistent system grounding; an example that comes to mind is the code requirement that a separate branch panel in a detached garage is often connected both to a local grounding electrode at the garage and back to the system ground bus (and through it to the main building grounding electrode) back in the main panel.

In general I'm nervous about any home-brew wiring solutions that, even if they seem to "work", may be unreliable, may be confusing to an electrician working on the building in the future, and can certainly add confusion to troubleshooting.

Bottom line on Updating Receptacles on a 2-wire Circuit

  • Don't install a 3-prong receptacle on a 2-wire circuit
  • Don't rely on the BX metallic jacket to serve as a ground path back to the electrical panel
  • Don't rely on a "daisy-chained" ground system such as a grounding conductor wire screwed just to the box, a second ground wire screwed from the receptacle green ground screw then connected to another threaded junction box location, etc. Bond the grounding conductors together and where a metal box is installed, also include a wire that connects the box to the grounding conductor.
  • Code compliance: any alternative local ground installation used to provide a true grounding conductor for a 2-wire circuit would have to be code compliant throughout its design, rout, and components.
  • Costs of grounding vs re-wiring: It seems to me that the trouble, time, and cost of installing custom, properly-wired new ground pathways connecting to each individual electrical box in an old 2-wire powered circuit would be quite a bit more than if we simply ran a new 3-wire circuit throughout.

Please let me know if I've misunderstood your question or the nature of your proposed 2-wire circuit grounding solution.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Critique and content suggestions are invited. Credit is given to content editors and contributors.

Is it Safe to Use a 3-Prong Adapter to Connect a 3-Pronged Appliance or Equipment Cord to a 2-Prong Ungrounded Electrical Outlet?

3 prong to 2 prong plug adapters for 2 wire electrical circuits (C) Daniel FriedmanReader Question: can I plug my TV into an ungrounded circuit?

5/14/2015 Chris said:

Hi, I just moved into a "new" home and all the receptacles are two-wire with no ground. Reading this, I don't believe it is safe to plug-in an adapter that ads the ground through the screw on the faceplate. However, our TV has the ground wire plug so I cannot use it.

Is here any option short of re-wiring to safely use devices that need the ground plug? Can I cut the cord on my TV and convert the plug into a two-wire style and forget the ground? (Also, we rent for now so I don't own the home). Thank you great article!

Reply:

Chris:

Do not cut or modify the cord to your TV. Doing so is unsafe and may also void the device warranty.

You are correct that it is not a good idea to connect a grounded appliance to an un-grounded electrical circuit. It is possible that there is a ground path available - you won't know until an electrician has examined your wiring.

And there are certainly three-prong adapters sold to plug into 2-prong receptacles such as the handful of them that I photographed atop this bureau in New Zealand. The 3-prong to 2-prong plug adapter typically has a tab that connects to the receptacle face plate screw - a feature that both secures the adapter in place and gives hope to the fantasy that there is an actual ground connection.

In fact there may be:

  1. a ground path for example may be through the three-prong adapter to two prong adapter's grounding wire or tab (see the illustration at above left),
  2. through the receptacle cover faceplate screw,
  3. through the metal strap around the receptacle to which that screw attaches
  4. to the metal ears that mount the receptacle to a metal (if it's metal) electrical box,
  5. through the screw or clamp that actually connect the receptacle mounting strap ears to the electrical box
  6. through the electrical box through an armored cable box clamp that secures the cable to the box,
  7. through the armored cable to the main electrical panel,
  8. through any armored cable clamps, boxes and sections that interrupt the circuit anywhere in its route between where you are using the adapter and the electrical panel (there could be many of these)
  9. through another cable clamp to the electrical panel box,
  10. through the electrical panel box itself to its grounding bus (in the panel) and
  11. through the grounding bus to a ground conductor that ultimately
  12. connects to a water pipe or grounding electrode at the property.

I gave this litany of at least a dozen connections in this makeshift electrical ground pathway to explain that if you use the adapter, your TV will probably work, and it might even have a "sort of" electrical ground. But in an unsafe situation such as a short circuit there are two hazards with this un-approved grounding approach:

1. the passage of the stray or shorted electrical current to earth has to go through multiple, potentially loose, unreliable screws, clamps, and connections that means that it may not work at all.

2. the grounded current - when it occurs - is passing not through a safe, properly-installed, code-approved grounding conductor wire but through the armored cable and other components not designed to carry current and that are exposed to touch. I watched a home owner, insisting his electrical system was safe, lick his knuckles and, standing on a damp basement floor, touch between a gas pipe and the outside of a "BX" or armored cable. He was shocked and knocked to the floor.

In sum, your TV will work, and it may be fine, in fact everything may be fine, until something isn't.

So the best approach is to install a grounded electrical circuit in the area(s) most needed, as soon as you can have that done. In the mean time if you decide to just buy and use a 3-prong to 2-prong adapter your TV will work but won't be properly protected.

 

Continue reading at GROUND WIRE CONNECTIONS or select a topic from the More Reading links shown below.

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CONNECTION for 2-WIRE RECEPTACLE CIRCUIT at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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