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Two-Wire electrical circuit questions & answers, FAQs:
Questions & answes about how to wire an electrical receptacle ("outlet" or "wall plug") or light fixture when there are just two wires (hot and neutral) but no ground wire. Questions & answers about using AFCIs and GFCIs on two-wire circuits.
This article series 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 seriesalso 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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I'm changing out 2 prong receptacles to two prong + ground receptacles on a two wire system. The boxes are metal. Is it acceptable to screw a bare wire to the box with a self tapping screw and hook to the ground screw? Do I need to check to make sure the box is grounded, if so, what is the best method? - Ben 10/9/12
Photo above/left shows a grounded receptacle (far left) and an un-grounded receptacle (at right in the same photo).
[Click to enlarge any image]
Watch out: no, what you propose is improper and unsafe even though it would "appear" to work. To add a grounding conductor or "ground wire" to a two-wire circuit you need to add a physical wire. The dangers of using the existing metal box and BX or armored cable for the ground path (I know that it's tempting) are several:
That path, which relies on numerous parts that can often be loose, is unreliable: the path is from the new grounded receptacle's internal grounding connector through a rivet to a metal strap on the body of the receptacle, through mounting screws through the receptacle's mounting ears, through a threaded hole in the metal receptacle box, through a metal BX connector which itself relies on at least four parts to be secured to the metal box, through a set screw from that connector into the armored cable, and thorugh god knows how many more sets of these parts down the entire remainder of the electrical circuit.
That path also is not intended to carry current, and should it do so in an emergency, someone touching the BX exterior could be electrocuted.
Finally, the receptacle manufacturer provides a ground screw on the receptacle that is intended to be connected by copper wire to a ground wire, parts and codes being ignored if you try using the box and its wire as the ground path.
On an ungrounded electrical circvuit you should install only two-prong, ungrounded receptacles - that is code compliant and that also lets users know that there is no reliable electrical ground present.
I have changed several receptacles in my 1994 home, but this time when removing the receptacle from the wall I see a third white wire attached to the side of the old receptacle. Can you explain to me what this third neutral wire is? - DW 6/12/12
DW, it is just too dangerous to claim to know what wiring connections someone has made in a building that is unseen and untested.
It would be common for an additional white wire connected to an electrical receptacle to be carrying the neutral line to another receptacle downstream. In other words the incoming neutral is connected to one terminal and the outgoing neutral is connected to a second screw that is electrically common with the first.
Check for a second hot wire also present in the same box.
At the end of a circuit, I'm only using 2 of the 4 screws on a conventional plug. What should I do with the 2 unused screws? Should they be screwed all the way in? Or left partially unscrewed? Or does it matter? - Chris Rasko 7/8/12
Regarding the un-used screw terminals on an electrical receptacle, you should simply screw them all the way in and leave them alone.
Don't remove the screws - it's not necessary, they are deliberately hard to remove completely, and they could be needed in some future wiring change.
Watch out: in some older installations the metal junction box is so tight that an extended, un-used wiring screw may be rather close to contacting the metal sides of the box. This can be particularly dangerous (risk of a short circuit) if down the road the receptacle becomes a bit loose in the box. I would screw the un-used screws all the way in to reduce this risk. I've also seen cautious electricians wrap the whole receptacle sides with electrical tape before pushing it back into a small box. One wonders if at that point, if we're that worried, we ought not to be installing a larger junction box.
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 started installing a box-extender on a receptacle in my kitchen because I'm tiling my backsplash and need to raise the outlet above the tile. However, the top screw connecting the outlet and box wouldn't hold. I spent way too much time bent double under my cabinets trying to get it to bite, but when I finally gave up and pulled it out it was stripped at the tip (which was as far as it'd go in). I'm sorry to bother you with triviality, but I'm new to home renos and don't know what to do. Advice? - Julia 1/29/13
Iif the problem is the screw itself is stripped, simply purchase a replacement screw or a handfull of them from your elecrical supplier. These screws are a standard thread and length, but longer versions are available at any hardware store.
For the case you describe, if the stripped problem is the mounting hole you'll need to either enlarge and tap the hole for tne next size larger screw, or purcase a clip-on adapter that slips over the stripped ear through which the original hole passed.
Taking care to move electrical wires out of the way of your drill bit, in a metal electrical box you can drill out the 6/32 screw opening to tap and accept an 8/32 screw.
For photos and step by step details on how to repair stripped electrical outlet mounting screws, see OUTLET BOX SCREW REPAIR.
(Aug 3, 2014) JR said:
I believe that the NEC (at least at one time in the past if not currently) allows replacing a 2-wire ungrounded receptacle with a 3-prong GFCI receptacle and leaving it ungrounded. The reasoning was the the GFCI circuitry would trip from the unbalanced hot-neutral current flow, obviating the need for a grounding wire.
I think it is not a perfect solution, but it may be an improvement over a std 2-prong outlet, and no one makes 2-prong GFCI outlets.
(May 5, 2015) vcr said:
can you wired GFI to a 2 conductors cable
JR yes, as we describe at INSTALL AFCI or GFCI on 2-WIRE CIRCUIT - I agree that a GFCI can add some safety features to an ungrounded circuit.
The risks of the approach you describe are several, such as providing a false indication that a safety feature is present when it is not, and other hazards not all of which do I list here.
When you test a GFCI using its test button an internal circuit exercises the trip mechanism.
When you test a GFCI using an external tester the tester creates a short to ground - the real ground - which doesn't exist in the case you describe. So we won't really know if the GFCI is going to protect the circuit nor under which conditions.
You are right that no one makes 2-prong GFCI receptacles, though there are certainly 2-prong standard receptacles available.
Generally you never want to install a 3-pronged electrical receptacle on a 2-wire circuit because it gives a false visual indication that a ground is present and permits the plugging in of grounded plugs from appliances that expect that ground to be there for safety - it's not present.
Perhaps placing the GFCI and AFCI protection back in the panel would be a better approach.
Yes you physically could wire up a GFCI receptacle to a two-wire circuit that does not have a ground. But there are some serious issues:
1. you cannot test the operation using the test and reset button as no ground is present
2. installing a 3-prong electrical receptacle on a 2 wire circuit is for other reasons unsafe and probably not permitted where you live. Its design suggests that a ground is present when one is not: a condition that is innately risky since some appliances require a ground for safe operation.
In my OPINION A better approach would be to put a GFCI breaker in the panel serving the circuit and to use only 2-prong electrical outlets.
(Nov 10, 2014) TJ said:
My daughter recently purchased a home built in the late 1960s. ALmost all outlets in the house are 2 prong.
Upon further investigation at several outlet boxes, I found that the wiring, although old (it's that old silver colored cable) it does actually have 3 wires , black,white and copper.
Looking in the outlet boxes, I can see that they actually took the ground wires and twisted them together.
These are all metal boxes btw.
I also checked a couple of the ceiling light boxes and found the same. Metal boxes, 3 wire cables, with the grounds twisted together.
Of these boxes I checked, some are grounded via a connection to these twisted together ground wires, and some are not.
I used a meter and checked from the hot leg, to the ground and it checks out in all cases.
next I went to the main breaker panel to see how that end of the circuits was and what I found was that the ground wire in each of these older cables (there are 4 or 5 of them total, leaving the breaker panel) are all actually 'grounded' to the cable connectors on the box, except for one of them, which is appropriately grounded to the ground bar in the breaker panel. Not sure why this was done this way, unless it was a left over from the original,old fuse panel and they didn't want to or couldn't extend this ground wire and attach to
So, a couple of questions.....
1- does anyone know why this was done this way (ie. i'm talking about the ground wire being attached to the cable connector where it enters the box, instead of the ground bar
2- is this considered an appropriate ground (thinking the ground wire is connected to the cable connector, which is on the box)?
3- I have no idea why this was done this way as the cable is 3 wire(hot,neutral,ground). The ground is there, but not
used in the fashion I would expect it to be
4- TO convert these two prong outlets to 'safe' 3 prong, can I just pigtail at each box the two ground wires in each cable and attach to the ground screw on the new 3-prong outlets AND ground to a ground screw on each box?
(Nov 10, 2014) TJ said:
Correction to prior post... house was build in late 1950s
So it sounds as if there is a proper ground wire but it was not connected to the receptacles themselves; one simply needs to make that connection when installing new, grounded receptacles. Don't forget to confirm that the ground wire circuit is complete back to the panel and to the required earthing connections at the building.
(Feb 6, 2015) Stan Muse said:
I have a two wire house. Why can't you just jumper the ground wire to the neutral wire on the 3 prong outlet? This provides a path back to the main panel for the ground. A three prong tester tests okay when this is done.
Because jumping the neutral to ground is
- can shock or even kill someone.
It may not be obvious to a normal person who's not an electrician, but the neutral wire in an electrical circuit carries current. If you then place that current on the grounding conductor or ground wire you are making the ground system live. Someone then touches a pipe, a metallic armored electrical cable jacket, the screw in a receptacle cover, or anything else connected to the grounding system and also touches ground and they get zapped.
Your tester may not indicate a problem but that's because it's not as smart as a GFCI, AFCI, or your local electrician.
(Feb 21, 2015) OldZeb said:
Avoid These Unsafe Practices When Wiring a 2-Wire (no-ground) Receptacle Circuit
Do connect the black wire to brass colored screw, white (neutral) wire to the white colored screw
Perhaps that sentence should be moved out of the UNSAFE PRACTICES paragraph for clarity.
Thank you OldZeb,
Good suggestion, we will edit the article accordingly.
(Feb 22, 2015) nathan10 said:
I recently extended the existing outlet to get a new outlet behind the wall mounted tv. The issue is that I have three prong outlet and have used the BX metallic conduit 3-wire to connect to the the existing outlet. However, when I opened the existing outlet, it only had two wires (black and white). There is a third wire that I see in the box but it seems to be Orange color and it is not connected. I connected the new outlet wires to the existing outlet (black to black and white to white) and then connected the green wire to the ground screw on the old outlet. Not sure if that is okay or not? But the new outlet does work fine. I can't seem to find any concrete answer on the Orange color wire (some sites say it could be high voltage line) so I didn't want to risk connecting green wire to that. have you seen this type of configuration? the house is not old, built in 2000.
We give details about electrical wire color codes for the US, UK and other countries
at ELECTRICAL WIRING COLOR CODES
There you'll see that in the U.S. orange is an alternate color for red=live additional phase (eg 240V), or for excepted voltage = a wire that remains live when others in that electrical box are off.
On an older 2 wire (hot and neutral only) electrical circuit without a ground, you should not install grounded electrical receptacles as doing so gives a false and unsafe suggestion that the electrical receptacle is safely grounded when in fact it is not. We discuss this in the article above.
Also do not use the metal jacket of the BX armored cable itself as a ground path as that too is unsafe.
For a home built in 2000 it is strange to find an ungrounded circuit, and improper. It is possible that someone used the wrong wire colours and that in your house the orange was supposed to be used as a ground - a mistake easily tested using a DMM or VOM in the hands of an electrician. if this is the case I have different advice.
1. Your electrician could label each orange wire in each box using green tape to show its a grounding conductor.
2. Watch out. Indicators that improper or amateur electrical wiring was done mean that there may be other improper and unsave wiring details that could electrocute someone or cause a fire. Therefore a more careful building wiring survey by a licensed electrician may be indeed needed,
(Mar 5, 2015) Leon said:
this old motor has two wiring post. The wires are old and I can't tell which are white or black. The top post has two wires connected and the other post has one wire connected. I tried to wire it to the electrical outlet on the wall but when I turned the motor off, it would trip the breaker.
Leon, if the motor trips the breaker I suspect either it's wired improperly or there is an internal short in the motor itself.
(May 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!
Thanks for the good question. I have posted a detailed reply along with a repeat of your question at ELECTRICAL WALL PLUG ADAPTERS
(June 11, 2015) Ben said:
Part of my home is 2-wire going to bedrooms and bathrooms. The bathrooms have GFCI installed in them. I had an electrician come in to see about making sure all circuits were GFCI protected. He suggested using AFCI circuit breakers instead of GFCIs at the bedroom outlets. Do AFCI circuit breakers work on 2-wire? Anything I should know about things that would not be protected with GFCI? (previous owner put 3-prong outlets in during remodel even though it is 2-wire circuit). Thanks!
Both AFCI and GFCI breakers will "work" in that in some unsafe conditions the device will trip off.
And GFCI devices are permitted on two-wire circuits by the U.S. NEC, as we describe at INSTALL AFCI or GFCI on 2-WIRE CIRCUIT .
However there are some concerns worth thinking about:
1. you cannot use the normal test buttons on a GFCI that depend on making an internal short to ground - as there's no ground
Also see AFCI GFCI TESTING & SAFETY
2. you are installing a 3-prong electrical plug receptacle or "outlet" onto a circuit where no ground is present. This is unsafe in that the appearance of the device suggests to future occupants that a ground is present when it is not, and because some devices may be unsafe when their design expects a ground to be present. In my opinion it's also an electrical code violation. That's why you can still buy and install 2-wire (ungrounded) electrical receptacles for installation on the circuit such as the one you describe.
What you can do is install the proper 2-wire, ungrounded receptacles and provide GFCI protection at the panel for the circuit that feeds those areas.
Depending on where the circuits are in use, some municipalities may require AFCI protection in the panel, for example for bedrooms,
See AFCIs ARC FAULT CIRCUIT INTERRUPTERS
and GFCI protection for high shock-risk areas such as kitchen, bathrooms, garage, basement.
See AFCI GFCI TESTING & SAFETY
Ask your local electrical inspector if she / he agrees with that approach. Keep us posted.
(June 28, 2015) Jason said:
Thanks for the great article. I have one quick question. I am [reading] many articles about running a line from an existing outlet when adding a new outlet, what about "tapping" into an existing line? For example, say you have a hot line running 2 feet above the floor, horizontally across the entire wall, can you add an outlet from that line?
Jason it's common to tap into an existing circuit to add a receptacle. However if your two-wire circuit is knob and tube wiring most jurisdictions do not permit extending or "tapping into" such circuits for extension. Instead you'll want to run a new circuit to that area - a desirable improvement both to avoid overloading an older circuit and also to provide electrical grounding required for many modern appliances.
(Aug 1, 2015) Hugh Gilmartin said:
Have just installed 2 AFCI breakers. When I energize the breakers they both trip. I have verified that the neutrals are not crossed. What gives?
Hugh as you may read at our article on AFCI breakers AFCIs ARC FAULT CIRCUIT INTERRUPTERS
- see - inspectapedia.com/electric/Arc_Fault_Circuit_Breaker_Interruptors_AFCI.php
nuisance tripping can be a problem, particularly if the breakers are using a shared neutral circuit.
I also had trouble with a coffee maker that kept tripping the AFCI. Take a look at that article and let us know if questions remain.
(Oct 5, 2015) vin said:
I have a question, i have a two wire (no ground) where there was a light before, i want to put a plug instead, i already bought a receptacle 20 amps and its has the ground green screw, should i put the outlet or buy a different receptacle?
I'm worried, Vin: a mistake in DIY wiring can kill someone or burn down the house.
Check to see if you're permitted to do your own wiring where you live, and be sure that proper permits and safety inspections are completed regardless of who does the work.
Check that you can put a 20A reptacle on the circuit: it may be a 15A circuit.
If a proper ground path is available in the junction box you may be able to properly hook up the receptacle if it fits in the box without overcrowding.
(Jan 10, 2016) Ray said:
I am installing an antique wall sconce that has just a black and an white wire coming from it. The box in the wall has a white and black wire coming out. There is no ground wire on either. Do I need to add a ground wire or is it safe to install with just the two wires
Your fixture will be safer if connected to a working ground wire (grounding conductor). If no ground is available, it depends: what does the manufacturer say in their product installation instructions?
(Feb 16, 2016) Anonymous said:
Is it OK not to have a ground or is that the nuetral (white)
On a TWO-WIRE (un-grounded) electrical circuit found in older homes, the wires are black (hot) and white (neutral) in standard simplest wiring.
The question of "OK" is another matter. A circuit without electrical grounding is notably less safe than one with a modern ground wire properly connected.
(Apr 24, 2016) Anonymous said:
.i have a blue and white wire is the .blue negative?
Anon you don't say in what country you live: wiring colour codes vary in different parts of the world. Please see ELECTRICAL WIRING COLOR CODES
(May 1, 2016) Joshua said:
Thank you for all this detailed information. My question may be ridiculous but what if I add a compasator to the ground screw to absorb a short? I guess I just wonder if that energy would return to the system or what granted I find a compasator with the ability to absorb the current.
I'm doubtful that you can buy and add an electrical device at each point where there is an electrical switch or receptacle or device that could provide that local protection from fire or shock in any economical manner nor one that would be approved. However the closest you might get would be to take a look at how GFCIs work on un-grounded electrical circuits.
(May 8, 2016) Elektro Man with strong current flowing said:
What if the 2 wires are the same colour?Does it matter which one is left or right?No earth by the way.
Yes Elektro, it matters a lot. While the AC circuit may appear to "work" with wires reversed you risk damaging equipment or shocking someone. An electrician or EE using a DMM or VOM can determine which is the current carrying wire.
[Sketch above provided courtesy of Carson Dunlop Associates, a Toronto inspection & education firm.]
2016/06/04 Chris said:
How can you wire a plug with no.colours colours on the wire
Good question, Chris. An electrician using a DMM or VOM would check each wire to identify which was the hot and which the neutral wire. Then s/he'd know to connect hot to brass coloured screw and neutral to white colured screw on the receptacle or switch. I usually also add a piece of black tape to the "hot" wire and/or a bit of white tape to the neutral wire to make it easier for the next guy.
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