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This article answers basic questions about false grounds and their related safety concerns.
Readers of this article should also be sure to see GROUND SYSTEM INSPECTION where we discuss 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.
© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
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.)
Three Slot Electrical Receptacles with False Ground
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, and False-Neutral Electrical Circuits in Older Homes
Ungruonded "two prong" Electrical Outlets - Two Slot Electrical Receptacles with No Ground
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Our photo (left) shows a polarized electrical outlet that does not provide a ground connection for a grounded plug. You can see that the two slots are of different sizes. This is an un-grounded outlet. If your outlets have two slots that are the same size, then they are neither polarized nor grounded. These are non-polarized or un-polarized, un-grounded electrical receptacles. You should not install grounded electrical outlets on circuits where no ground path is actually present (such as knob and tube wiring). To provide a grounded outlet where no ground is present is dangerous. Some locations in your house- especially where the outlet and/or appliances may become wet- require ground-fault circuit-interrupter (GFCI) receptacles. Older, ungrounded circuits usually are protected by polarization, which is less effective than grounding but better than nothing. Grounded and polarized receptacles work only if they are wired correctly. |
False Neutral: Electrical Receptacle Wiring Connects Neutral Screw to Ground Path
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If you look closely at bottom connecting strap below the face the electrical outlet show above, just above our red (C) notice, you'll see a white-painted wire wrapped around the metal strap used to mount this connector in the electrical box.
Unlike the earlier "False Ground" case, this electrical receptacle was wired with a "false neutral" using bell wire or telephone wire. The receptacle was mounted in a metal junction box and wired with two-wire armored cable (BX) that contained a hot and neutral wire. But a fault in the neutral wiring in this building caused the receptacle to stop working. A previous owner or handyman "fixed" this problem by making a flimsy connection between the neutral screw on the receptacle and the receptacle's mounting ("ground") strap. Since the circuit wire was armored cable, a path to ground was provided by the metal jacket of the wire itself. But when the amateur electrician wired the receptacle as we found it, plugging anything into the receptacle completes a circuit from the hot side of the receptacle through the powered device (say a vacuum cleaner), back to the neutral side of the receptacle, and through that telephone wire off to the mounting strap which connects to the metal junction box and the BX metal jacket that completes a circuit to earth, rather than through the proper neutral wire. What happens when you use this unsafe electrical receptacle? Well when that vacuum cleaner is running the return current is traveling on the armored cable jacket - the metal "BX" exterior as well as other components in the electrical system become live. Just touching the "BX" wire jacket and grounding yourself, say to a radiator, can give a nasty shock - which is how the author discovered this erroneously wired device. |
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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
GROUND SYSTEM INSPECTION
Why Grounding is Needed
Gas Piping Ground Bond
Table of Ground Wire Sizes
False Ground at Receptacles
False Neutral Connections
Case History: Double Fault Leads to Loss of Power
Case History:Loss of Neutral Shocks Homeowner
Electrical Service Grounding Checklist
- Jim P. Simmons, Licensed Electrician, 360-705-4225 Mr. Electric, is a Licensed Master Electrician in Olympia, Washington. Contact Jim P. Simmons, Licensed Master Electrician, Mr. Electric, 1320 Dayton Street SE Olympia, WA 98501, Ph 360-705-4225, Fx 360-705-0130 mrelectricoly@msn.com
- Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
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