One of the problems that comes with owning with an older home is that the three-prong cords on many modern electrical devices will not plug into pre-1960 two-slot receptacles. One way to deal with it is to use an “adapter” like the one shown above, which allows you to plug in your three-prong cord, but does not actually provide the required safety of a connection to ground that is the purpose of the third prong. Investors who remodel older homes for resale know that those two-slot relics turn off today’s homebuyers, so they routinely upgrade all the receptacles in the home to three-slots with shiny new cover plates.

    Ethical remodelers recognize that the third slot adds necessary shock protection for the homeowner. If they change-out to three-slot receptacles, the new ones need a ground wire run to each receptacle or, as an alternative, protected with a GFCI-device.

  But those options are expensive. The cheap-and-dirty solution is to install the new receptacles with no ground connection at all. This is easily detected by a three-light plug tester available at any hardware store, like the one shown below. When only the center orange light goes on, that means the circuit is ungrounded.

    Many inspectors rely on a three-light tester for verifying that a receptacle is correctly wired. Unfortunately, there is a way to trick a three-light tester into confirming that a receptacle is grounded when it actually is not. It is termed a false ground, although electricians routinely call it a “bootleg ground” or “cheated ground.” When upgrading to a three-slot receptacle in a two-wire system without a ground wire, if you use a short “jumper” wire to connect the ground screw at the side of the receptacle to the adjacent neutral screw, the connection will deceive a three-light tester. This is because the tester can recognize that the new ground slot will accept the flow of electricity, but cannot determine if the ground and neutral are traveling along the same path.

    This wiring configuration can cause electrical shock, or damage equipment that utilizes a ground while operating. The electric shock potential is due to the fact that the ground prong in a cord is connected to the metal frame of the appliance. With a false ground, the frame becomes connected to the neutral instead, and any connection of the frame to a grounded object will result in current flow. If that connection is a person, there is the possibility of a fatal shock.

    Two different $300 plug-in receptacle circuit analyzers (Ideal Suretest 61-165 and  Amprobe INSP-3) will indicate the presence of a false ground. We prefer the Amprobe, shown below, but both are good. A simpler, although more time-consuming, test method is to open a couple of receptacles and check the wire connections for that jumper wire when examining three-slot receptacles in a pre-1960 house—after shutting off the breaker, of course.

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  To learn more about electrical wiring, devices, and receptacles, see these other blog posts:

 • What is the difference between what trips a GFCI (ground fault) receptacle and a circuit breaker?

• Why is an opening in the wall around the side of an electrical receptacle outlet a safety defect?  

• When was GFCI-protection for kitchen dishwasher receptacle outlet first required? 

• When should I replace electric receptacle outlets? 

• What are "self-contained" electrical receptacle outlets and switches?

• What is the difference between an electrical receptacle, an outlet, and a plug?

• Does a washing machine receptacle outlet require GFCI protection?

• What is the building code requirement for receptacle outlets at stairs and stair landings?

• What is a "backstab" receptacle outlet? 

• Why are some electric receptacle outlets upside down (ground slot up) in a house?   

• What is the height requirement for an electric receptacle outlet? 

• Where are GFCI receptacle outlets required?

• Does a home inspector remove receptacle outlet cover plates?

• When was the current receptacle/outlet spacing of 12-feet first required? 

• When was the three-slot (grounding) outlet/receptacle first required? 

• Why does painting an electric receptacle (outlet) make it unsafe?

• Why are electrical outlets and plugs polarized? 

• How many electrical receptacles (outlets) are required in a hallway?  

• Is a house required to have outdoor electric receptacle outlets?

• How I can tell if a receptacle outlet is tamper resistant?

• How can adding wood paneling or a wainscot create an electrical safety hazard?

• How far apart should kitchen counter receptacles be spaced?  

• What is reversed polarity at an outlet/receptacle? Why is it dangerous? 

• How can I tell if the electric receptacle outlets are grounded? 

• How far apart should the electrical receptacles be placed?

• What are the most common problems/defects found with electric receptacle outlets during a home inspection?

    Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.