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ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
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FIRE SAFETY Checklist, CPSC
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KNOB & TUBE WIRING
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LOW VOLTAGE BUILDING WIRING
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MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
MURRAY SIEMENS Recall
PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS
REMOTE ELECTRIC POWER, PHOTOVOLTAIC
RUST in ELECTRICAL PANELS
SAFETY for ELECTRICAL INSPECTORS
SE CABLE SIZES vs AMPS
SIEMENS MURRAY Recall
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
UNDERGROUND SERVICE LATERALS
VOLTS / AMPS MEASUREMENT EQUIP
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
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 and Safe Electrical Inspection Procedures for Inspectors examining Residential Electrical Systems and Local Electrical Grounding for safety procedures during inspection of the grounding system.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Sketch at page top courtesy of Carson Dunlop Associates.
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.)
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.
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.
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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