Conventional duplex receptacles have two places to plug-in devices. As shown in
the illustration, newer receptacles have a half-round hole that receives the grounding
plug on an electrical cord. A contact leads from this hole to a green grounding
screw that should be connected to the house ground (metal conduit or a green wire)
to provide protection against shock when an appliance is plugged in. It's always
best to check with a licensed and qualified electrician, like an Excellent Electrician,
if you're not sure about your type of electrical system.
Some receptacles in older homes don't have grounding plugs-they have only the paired
slots. If your home's receptacles are like these, you've probably discovered grounding
adapters, those little plugs that convert the end of a three-pronged plug to two
Outdoor receptacles are mounted with special covers that seal the weather out (standard
types are not safe for outdoor use). A ground-fault circuit interrupter, also called a GFI or GFCI, shuts off a circuit
instantly if it senses a hazardous short.