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Are two-prong outlets up to code and legal?
Monday, April 6, 2020
Existing ungrounded two-prong receptacle outlets are allowed to remain in place by the National Electrical Code [NEC 406.4(D)(2)], and they can also be replaced with another two-prong receptacle at locations where a ground connection does not exist, if you want. But, while two-slot receptacles are reasonably safe when used correctly, three-slot (grounded) receptacles are ultimately safer and better for avoiding a shock or electrical fire. If you are able to upgrade to a grounded or GFCI receptacle, it’s definitely a good idea. That’s why the code was changed 50 years ago to require them for new construction.
And here’s an additional problem: lots of electric appliances used today have cords with three prongs. Using an adapter, like the one shown connected to the top half of the receptacle pictured above, is not a safe solution to the dilemma. Theoretically, if the metal ring at the two-slot side of the adapter is connected to the securing screw for the receptacle cover plate, then the ground slot is connected to a ground. But that is almost never the case and most people don’t even bother connecting it—with the result that an appliance that requires grounding to be safe, such as a refrigerator or washing machine, is ungrounded.
Even worse is a defect we sometimes see in older homes, where the old ungrounded receptacle is changed out for a three-slot receptacle but there is no ground connection made. A three-light circuit tester, like the one shown below, is used by many home inspectors to check for this safety defect. Two orange lights means the circuit is grounded, and one orange lights indicates lack of ground. Unfortunately, this little tester does not detect what is called a “false ground,” a condition in which the ground slot is connected to the neutral wire in the circuit—which is also unsafe. Detecting a false ground requires a more sophisticated electronic testing device.
There are three safe and code-approved ways to repair an ungrounded three-slot receptacle:
- Run a ground wire to the new three-slot receptacle. This is often the most difficult and expensive solution.
- Install a GFCI (Ground Fault Circuit Interrupter) receptacle. It’s the kind with two small push-buttons in the center. A GFCI shock-protection device is considered an acceptable alternative to a ground connection, but the receptacle cover plate must have a small sticker (provided in the box with the receptacle) attached that says “NO GROUND PROVIDED.”
- Replace it with a two-slot receptacle, which is still manufactured and available on the shelf at many hardware stores. If not, they can special-order it for you. Since having just one three-slot receptacle in each room is adequate for most homes, this solution is satisfactory for many of the ungrounded three-slot receptacles.
Many appliances require a ground connection to operate properly and have a manufacturer’s sticker, like the one shown below on side of a fluorescent ceiling fixture, that states “FIXTURE MUST BE GROUNDED for safety and proper operation.”
Also, see our blog posts Can you plug a surge protector into a two prong outlet? and How can I tell if the electric receptacle outlets are grounded?
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To learn more about electrical wiring, devices, and receptacles, see these other blog posts:
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