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Old house electrical ground wiring: this article answers basic questions about residential ground wiring & electrical grounding safety in older homes. Readers of this article should also be sure to see our main article on electrical grounding at ELECTRICAL GROUND SYSTEM INSPECTION. This article explains the more broad topic of electrical grounding. Also review SAFETY HAZARDS & SAFE ELECTRICAL INSPECTION PROCEDURES for Inspectors examining Residential Electrical Systems and Local Electrical Grounding for safety procedures during inspection of the grounding system.
Sketch at page top courtesy of Carson Dunlop Associates.
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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 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.)
Do Older Homes Have Proper & Safe Electrical Ground Wiring?
Often an older building has poor or no working local electrical ground, relying instead on the incoming neutral wire from the electrical service.
Or the building's main electrical ground may have relied on connection to a metal water pipe connected to a well; we've found building ground wires connected to a metal water pipe which used to run out of the building and into earth (possibly a pretty effective ground) but where the metal piping exiting the building had been replaced with a newer plastic water line between the well and the building. In other words the local ground was completely ineffective.
Modern electrical grounding at residential properties requires use of one or more grounding electrodes connected by an un-spliced wire between the electrode and the ground and neutral bus in the main electrical panel.
Bare aluminum electrical ground wires are sometimes found to have corroded entirely through where the wire touched a damp foundation wall. We also find that the ground wire between the electrical panel and a building water pipe or grounding electrode has become separated, loose, spliced, or lost entirely, as shown in our photo.
Two Slot Electrical Receptacles with No Ground
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. This leaves you with no protection against shocks from defective fixtures or appliances using that outlet. At the very least, you need to install polarized outlets. You cannot and 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.
An older home may have electrical service that is inadequate or even unsafe. It can be confusing, as well. If you are unsure about your home’s wiring, have a professional check it out. See False Ground at Receptacles and False Neutral Connections for examples of how wiring mistakes on un-grounded or even grounded electrical circuits can be dangerous.
Other Electrical Ground Wiring Problems in Older Homes
Here are a few things to consider when inspecting the electrical system in an older home.
Warning: this list of electrical wiring defects and safety concerns in older homes is incomplete. Contact Us to suggest corrections, changes, or to add additional items.
Please see KNOB & TUBE WIRING for a detailed discussion of the identification, inspection, and repair of this electrical wiring system.
Knob and tube electrical of wiring has been installed in homes from the 1920s right up into the 1970's in some jurisdictions.
Knob and tube electrical wiring may be functional in a home and it was in its original concept a safe wiring method, separating the two conductors in air (see our photo at left) and using durable ceramic insulating knobs and tubes to mount the wire.
Knob and tube electrical wiring may not need to be replaced, but it certainly deserves careful inspection and possibly replacement or repair, because knob and tube systems lack an electrical ground (less safe), may have damaged insulation (less safe), or may have been improperly modified or extended (unsafe).
Loose taped wires, old wire damaged because it’s exposed, and multiple wires slipping off a single terminal screw may seem like minor problems, but are not.
See Electrical Circuits, shorts for more about short circuits, how they happen, how they are corrected.
For an example of installing an additional electrical receptacle, see Electrical Outlet-how to add.
"Polarity" in an electrical receptacle and on the device that plugs into or connects to it means that we're making sure that we connect the "hot" or "live" side of the electrical circuit to the connection point in the appliance or device that was intended to be "hot" or "live".
Carson Dunlop's sketches show why it's important to respect polarity when connecting an electrical receptacle, a lamp or any other appliance.
Never clip or file down the prongs on a grounded or polarized plug in order to force it to fit into an older electrical receptacle. The risk is that your plug will be installed with reversed polarity - connecting the "hot" side of the electrical circuit to the normally neutral-wired side of the appliance. We've found appliances (a coffee maker) that simply burned up when connected in this fashion.
Go to the heart of the problem: Test and upgrade your electrical circuit system.
See ELECTRICAL GROUND SYSTEM INSPECTION for details about how to inspect the electrical grounding system at a building. Also, see details about electrical grounding at Electrical Circuits, shorts, and at Electrical Wiring in Old Houses and at Electricity Basics - how it works.
Watch out: Safety Warning: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death.
Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by setting a circuit breaker to OFF or removing a fuse. See SAFETY for ELECTRICAL INSPECTORS and Electrical Wiring Books & Guides
Elizabeth Sluder contributed to the original text of this article. Readers of this article should see ELECTRICAL GROUND SYSTEM INSPECTION and also see ELECTRICAL DEFINITIONS. This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Critique and content suggestions are invited.
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