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False electrical ground inspection & detection: this article answers basic questions about false grounds and their related safety concerns. Readers of this article should also be sure to see ELECTRICAL GROUND SYSTEM INSPECTION where we describe the more broad topic of electrical grounding, and also review Safety Hazards and Safe Electrical Inspection Procedures for Inspectors examining Residential Electrical Systems and Local Electrical Grounding for safety procedures during inspection of the grounding system. Page top photo is courtesy of Jim P. Simmons - Mr. Electric.
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Our photo at left shows a home wired with knob-and-tube circuitry. A knob and tube circuit does not include a grounding conductor or "ground wire" so any receptacles or other devices powered by such a circuit will normally lack the added safety of electrical grounding.
But electrical wiring errors combined with hasty inspection and testing may lead an inspector or homeowner to think that a device such as an electrical receptacle on such a circuit is "grounded" when it is not. Here we provide photos and discussion of such a case.
Older homes often have electrical receptacles and fixtures that are ungrounded, and many local codes do not require that they be rewired so they're grounded. Still, grounding is worth adding to your system because it adds protection against electrical shock. Grounding provides a third path for electricity to travel along, so if there is a leak of any sort, it will flow into the earth rather than into the body of a person who touches a defective fixture, appliance, or tool.
An electrical system is grounded with a local grounding rod driven at least 8 feet into the ground outside the house or by connecting to a cold water pipe. Each individual branch circuit must be grounded as well, either with a separate wire that leads to the neutral bar of the service panel or with metal sheathing that runs without a break from each outlet to the panel. (In theory, electrical outlets can be grounded individually, but this is impractical.)
In some older homes we find incorrectly installed "grounded" electrical outlets that have the opening for the grounded plug ground connector, but the electrical system has no ground path present. If you are replacing an electrical receptacle on an ungrounded circuit you should use two-slot non-grounded electrical receptacles.
But worse than installing a "grounded-type" electrical receptacle on an electrical circuit where no ground is present, is the dangerous step that a few amateurs take of connecting the receptacle's ground screw to the neutral or white wire in the circuit.
Jim Simmons is a professional and licensed electrician who studies electrical field failures and unsafe electrical wiring. His photos at left and below show an improperly wired electrical circuit that provides a "false ground" by making a connection from the neutral wire to the ground screw. This connection may make it appear that the circuit is "grounded" since a test that connects the hot side of the receptacle to the ground port will show current flowing, but this is incorrect.
Not only does a "false ground" electrical receptacle lack an actual safe alternative path to earth through a separate ground path or grounding conductor, but worse, the "ground" connection, by being wired to the neutral side of the circuit, can cause dangerous electrical shock as well as damage to equipment plugged into such an electrical outlet.
A safer repair would be to install new electrical wiring that provided a ground path along with grounded electrical receptacles.
Mr. Simmons wrote "A simple $7 tester will test this outlet as OK. The Ideal tester I use clearly shows FG on the display, or False Ground. I have seen it many times over the years but this is the first time I got good pictures of it. You can see the copper jumper from the ground terminal to the neutral."
See ELECTRICAL GROUND SYSTEM INSPECTION for details about how to inspect the electrical grounding system at a building.
Ungrounded "two prong" Electrical Outlets - Two Slot Electrical Receptacles with No Ground
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