There are several reasons you might consider upgrading or replacing outlets in your home. The most common is the need to replace old two-prong outlets with more powerful three-prong models.
Safety Note—Always use extreme caution when working with anything electrical. When working with wiring, always turn off the relevant circuit breakers and test the lines to make sure they're not live. In some places, you may need legal certification to complete advanced electrical projects.
International Note—This article discusses outlet types common to the USA, Canada, and Mexico. The basic principles apply to outlets of all kind, but details may vary by country.
The 2-Wire Ungrounded versus the 3-Wire Grounded Electrical Circuits
The old two pronged outlets provided 120 volts to your circuit from the black Hot line, with a return path through a Neutral line in order to complete the circuit to the main panel. Despite lacking a protective direct connection to the ground (Gnd), this became the adopted electrical system from the origin of distribution systems up to the early 1960s.
The problem with an ungrounded circuit is that when an appliance’s Hot line gets shorted out to its chassis due to a breakdown or some other malfunction, the chassis, which isn’t connected to anything at all, becomes live with a full potential of 120 volts.
This short in the system creates an unintended shift in a circuit still seeking the shortest path to earth, which your body would provide should it come in contact with its metal casing.
So in the early 1960s, it became obvious that a 3rd wire needed to be added to the electric cable to connect all the electrical boxes and the outlets’ casings within a circuit to a 3rd semi-circular female connector on the receptacles end while its direct connection to a ground bus bar inside the breaker panel’s end would now provide the easiest path to earth (or ground).
Should a short circuit then make an electric box or an appliance become live, the current would simply flow from its metal casing through the semi-circular male mating prong of the appliance’s plug which would connect it to this added Gnd wire, right down to the Gnd bus bar tripping the breaker and cutting off the power to the circuit.
This Gnd wires system, therefore, greatly reduces the risks of electrocution by connecting all the metal components within any circuit connected to a ground wire should a live wire be damaged, pinched, or otherwise caused to leak to a chassis or to Gnd.
Along with reducing the risks of electrocutions by providing a more direct and easy path to ground for stray currents, this grounded wiring system also provides tremendous protection for all your electric and electronic equipment from high-energy transient over-voltages or power surges that can sometimes be induced into your electrical system.
Questionable Alternatives Used with Ungrounded Circuit
Doing a complete re-wiring of a house can prove to be a very costly and frustrating undertaking, so if you own or if you’re planning on buying an older home, you should beforehand have a look at its electric panel to find out if the circuits all have the properly grounded wiring.
Although ungrounded installation can be possibly detected by going around the house and checking all the outlets with an outlet tester (Fig 1), you should be aware that the outlet tester is not infallible, especially when dealing with pirated outlets, and that even if it displays a positive result, it can easily be cheated by the Bootleg practices. There are also more ways to cheat the missing ground.
1 - With two-prong outlets installed over many years and the newer appliances coming up with three-prong plugs, many DIYers took the easy way out by simply cutting off the circular prong from the appliances’ cord in order to be able to plug it in.
A lot of extension cords also ended up that way, and while the modification seems to work, it simply makes people complacent in ignoring the risks involved in following such practices.
2 - In other situations, a two-wire circuit is simply cheated by installing three-prong receptacles without a proper connection to the ground just to make sure that any appliances with three-prong plugs can be used without removing the Gnd prong.
By disregarding the female Gnd connection the substitution looks good but it still leaves you with an ungrounded hazardous circuit and such practices are totally illegal.
Such a practice is prohibited by the NEC unless properly wired GFCI devices are used at the outlet or at the breaker panel to provide extra protection against electrocution.
3 - Also illegal is the bootleg outlet connection, as shown in figure 2, which is mainly practiced as a way to fool the inspectors who quickly check around with an outlet tester and take the tester readings for granted.
Since the outlet tester basically checks voltages between the Hot and Neutral, the Hot and Gnd, and the absence of voltage between the Neutral and the Gnd, it is not difficult to cheat by simply connecting the Gnd terminal to the Neutral terminal, making it look like the Gnd terminal is actually grounded.
But this is not what’s happening since the terminal is simply connected to the Neutral line’s return path while also connecting the Neutral to the conductive casings, appliances, or fixtures, thus creating a strong possibility of energizing the casing through the neutral current-carrying conductor.
The GFCI Receptacles and How They Work
There are certain devices that can prevent the risks of electrocution and called GFCI sensors which consist of a solid-state circuitry that constantly monitors the current flow in a circuit, comparing the current flowing through the “Hot” black wire with the current flowing back through the “Neutral” conductor.
When the GFCI detects a difference of 5 mA (0.005 A) or more between the two lines—created by a leak from the Hot line to the ground and known as a ground fault—the receptacle’s sensor activates the “ground trip,” opening the circuit.
The GFCI outlets look very much like the regular outlets except for the two buttons in the center used to test and reset the outlet, as well as a pilot light showing its status (see Fig. 3).
It should be noted, however, that used on any ungrounded installations, the GFCI receptacles should all be duly labeled as “No Equipment Ground,” for it does have some disadvantages.
Even when a circuit is missing a ground connection, GFCIs can detect the differences in current between the Hot and the Neutral line making the GFCI outlet an efficient system for preventing electrocution.
GFCIs will not do as well where transient over-voltages are induced from sudden impulses of high energy from lightning strikes, arcing, unfiltered electrical equipment, or other sources.
You should also be warned that a plug-in outlet tester will work differently when you use it to test an ungrounded GFCI outlet, and that ground fault can only be effectively tested with the “test button” on the receptacle itself.
Fixing Ungrounded Circuits
Just because you’ve installed GFCI receptacles all over the house doesn’t make the electrical system any more grounded, and although the GFCI outlet will sense the ground fault and trip it or shut it off, it will not protect your equipment or your electronics from transient over-voltages from the sudden impulses of energy induced into the circuit from various sources, one being from lightning strikes.
Rewiring is the only real option that can safely ground the outlets. If you’re considering it, the first step would be to consult with a certified electrician and make a list of all the implications that it might involve.
If the electrical is not grounded, it probably has an older panel much too small for today’s needs and will probably need to be replaced—especially if it has fuses. Then every cable that doesn’t have a ground wire will also need replacement, which implicates fishing cables through walls and ceilings.
Choosing the Right Receptacle for a Specific Use
While standard 15-amp receptacles are suitable for typical appliances such as lamps, TV monitors, small kitchen appliances (electric knife, hand blender, etc.), and other low-power accessories, 20-amp outlets should be installed wherever you have or plan on using heavy-duty or high power appliances and tools.
* Kitchens are required by code to have two 20-amp circuits on every countertop to power simple common appliances like toasters, blenders, microwave ovens, stand-mixers, etc. All counter surface outlets should also be GFCI protected.
* Bathrooms must also be wired with 20-amp GFCI receptacles (or a circuit breaker).
* Laundry room should be equipped with at least one 20-amp GFCI outlet dedicated to the washer, and every other 15 and 20-amp must also be GFCI protected.
* Living rooms, family rooms, and bedrooms should also be provided with 20-amp outlets near windows and wherever high-power devices, such as space heaters, air conditioning units, etc. are to be plugged into.
* Every 15 and 20-amp outlet in the basement, crawlspaces, garage, and outdoors should also be GFCI protected by code.
If you’re in the process of installing an outlet, either replacing an old one or adding a new one, you’ll have to make sure of your specific needs and what type of outlets you should use for the job. Here’s how to differentiate each different type-
A) The grounded 3-prong 15 Amps 120 volts outlet with a shorter slot for the “Hot” line, a longer one for the “Neutral” line, and a third semi-circular one for the ground wire is the most commonly used outlet around the house and should only be used with 14/2 wires and a 15 amps circuit breaker.
It should never be used, however, to plug in a space heater or other high-power devices, or a power bar loaded with too many devices such as a TV screen, AV units, a cable box, etc.
B) The 3-prong 20 Amps 125 volts receptacle basically has the same appearance as the 3-prongs 15 Amps, except for a longer slot that is shaped as a sideways “T” letter (see Fig. 4).
The outlet is designed to withstand a greater power consumption from appliances for up to 20 amps without heating up but must be wired up through a heavier 12 gauge wiring that can withstand the extra load.
Such outlets are better suited for washers, dishwashers, space heaters, and around the kitchen counters where you plug-in multiple appliances such as microwave ovens, toasters, etc.
C) While GFCI offers important safety protection against shock hazards and electrocution, there is another type of monitoring outlet called “Arc Fault Circuit Interrupter” or AFCI, which—although identical to the GFCI in appearance—provides protection from electrical fire hazards.
AFCIs are designed to detect arc faults within their circuit resulting from power leaks or shorts to ground caused by faulty wiring or defective appliances causing the circuitry to trip the AFCI’s internal contacts. Both of these types of receptacles should be chosen by amperage rating.
D) Modern receptacles are also available with a “tamper-resistant” device, as they are equipped with built-in barriers behind the slots that only open when the hot and the neutral prongs are inserted simultaneously into the receptacle.
Inserting an object into one of the prongs only is not possible with this type of outlet, making it safe and ideal in rooms with children.
Installation #1 - How to Add an Outlet to a Circuit
1.1 - Use a stud-finder to locate the stud closest to your chosen location for the new outlet. You can then run the stud-finder up and down to locate any noggings in the framing that might be in the way, as you may be required to drill through or notch to get the cable to the attic or to the basement.
1.2 - Locate the closest and the most practical outlet that you can get power from. Take into consideration that you should comply with the 80% circuit breaker load rule with the allocation of 1.5 amps per receptacle—a 20 amps circuit for example would allow for 80% of 20, which is 16 amps divided by 1.5 amps per outlet, which would allow 10.6 rounded off to 10 receptacles within the circuit.
1.3 - Trace out the outline of the electrical box on the wall right next to where it will be sitting against the stud unless you have a box with the mounting brackets that lets you install it anywhere on the wall.
1.4 - Using a keyhole saw, a utility knife, or a power tool such as a rotary tool, cut out the opening for the box.
1.5 - Install a junction box along the path of the cable you’ll be tapping from and secure it in place next to the cable.
1.6 - Cut the cable making sure each section is long enough to provide 6-inches or more inside the box once installed, removing some of its protective jacket and skinning the insulation at the ends.
1.7 - Get a length of cable of the proper gauge size for the new outlet and after preparing one end of the cable the same way as in step 1.6, install all three cables in the junction box, securing them with their respective cable connectors and connecting all the ground wires together to the box.
1.8 - Either working from the attic or from the basement, bring the new cable to the section of the wall where you want to install it and drill a hole through the wall plate or the sill plate and push the cable inside far enough to reach the opening of the outlet box.
Note - If there happens to be a nogging on the frame blocking the cable’s path toward the outlet opening, you will either have to drill through the nogging to get the wire through or notch from outside the drywall.
You only need a narrow slot—just long enough to create the necessary openings to let the cable out from one side of the nogging and back into the other side once an opening is created through the nogging by extracting some of the wood to create a concealed pathway to pass the cable through.
As one might expect, this particular process will also involve extra drywall repair later on.
1.9 - Catch the end of the cable next, pulling it in through the outlet opening, and again, remove some of the jacket and the insulation before installing it in the electrical box, connecting the base of the ground wire to the box.
1.10 - Push the electrical box into its opening and secure it in place. After choosing the right receptacle, connect the hot, the neutral, and the ground to it, then install it securely in the box.
1.11 - Return to the junction box and connect all the black wires together, then the same for the white and finally the ground wires. Place them all snuggly inside and secure the cover on the box.
1.12 - Switch the circuit breaker back on.
Installation #2 - How to Replace an Already Existing Receptacle
You could also have to replace a defective or damaged receptacle or simply upgrade it to a GFCI or AFCI outlet with the proper wiring already in place, but before you start working at it you must make sure that all power is removed from the line.
2.1 - Shut off the circuit breaker that is assigned to that circuit at the electric panel.
2.2 - Make sure that there is no longer any power flowing through the circuit by taking a voltage reading at the outlet, or plugging in a voltage or outlet tester, to confirm it.
2.3 - Remove the outlet cover and then the receptacle from the electrical box and disconnect all three wires going to the receptacle—the Hot, the Neutral, and the ground wires.
2.4 - Choose the right receptacle—if you’re fixing a 20 amps outlet, make sure to check the breaker rating for 20A and the wiring to be at least 12 gauge, and if it is a 20A circuit, choose a receptacle at 20A rating.
If it’s not a 20A circuit, however, but a 15A. DO NOT use a 20A receptacle at the outlet as this might mislead someone into trusting it to be 20 amps and use it to plug in larger appliances or tools and cause the wiring to heat up.
2.5 - Connect each of the three wires to the new receptacle and replace it inside the electrical box, securing it in place.
2.6 - If you’ve installed GFCI or an AFCI receptacle, press the test and then the reset button to make sure it all works perfectly. Put on the cover and screw it back in place.
For more information on electrical outlets, check out our pieces on how to add an electrical outlet next to a light switch or how to repair an electrical outlet.