Although polarized outlets and plugs were introduced in the 1880s, they were not popular at first and did not become standard until the mid-20th century. The earliest National Electric Code (NEC) that we can find that references polarized receptacles is the 1962 edition, which required outlets to be both grounding (3-prong) and polarized. We occasionally see an unpolarized outlet still in place in a vintage home with ungrounded 2-slot receptacles—like the battered, burnt, and ready-for-retirement one shown below.
To learn more, see our blog post Why are electrical outlets and plugs polarized?
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To learn more about electrical wiring, devices, and receptacles, see these other blog posts:
• What is the difference between what trips a GFCI (ground fault) receptacle and a circuit breaker?
• What is the code requirement for GFCI protection for receptacles near a wet bar sink?
• What is the requirement for a service receptacle outlet for heating, air conditioning, and refrigeration (HACR) equipment?
• Why is an opening in the wall around the side of an electrical receptacle outlet a safety defect?
• When was GFCI-protection for kitchen dishwasher receptacle outlet first required?
• What is allowable voltage range at a wall receptacle outlet in a house?
• When should I replace electric receptacle outlets?
• Does an electric receptacle outlet in a storage shed require GFCI protection?
• What are "self-contained" electrical receptacle outlets and switches?
• What is the difference between an electrical receptacle, an outlet, and a plug?
• Does a washing machine receptacle outlet require GFCI protection?
• What is the building code requirement for receptacle outlets at stairs and stair landings?
• Can I remove a 240-volt range receptacle and hard-wire the range?
• What is a "backstab" receptacle outlet?
• Why are some electric receptacle outlets upside down (ground slot up) in a house?
• What is the height requirement for an electric receptacle outlet?
• Where are GFCI receptacle outlets required?
• When were GFCI receptacle outlets first required?
• Does a home inspector remove receptacle outlet cover plates?
• What is the minimum height for an exterior receptacle outlet?
• When was the current receptacle/outlet spacing of 12-feet first required?
• When was the three-slot (grounding) outlet/receptacle first required?
• Why does painting an electric receptacle (outlet) make it unsafe?
• How many electrical receptacles (outlets) are required in a hallway?
• What problems does having too many electric receptacle outlets on a single circuit cause?
• Is a house required to have outdoor electric receptacle outlets?
• How I can tell if a receptacle outlet is tamper resistant?
• Why is there a GFCI breaker in the electric panel for the bathroom shower light and exhaust fan?
• What is a false ground, bootleg ground, or cheated ground receptacle?
oblems/defects found with electric receptacle outlets during a home inspection?
Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.