Layout

• An electrical outlet provides three kinds of electrical connections. The first, called hot, is the source of the electricity. The second, neutral, is the electricity's return path back to the household circuit breaker box and ground. The third, ground, is an independent return path provided for safety.
  
  

NEMA 1-15

• The original socket style for American homes, NEMA 1-15, provided hot and neutral as two thin, parallel connections. It didn't have a ground connection. On the early version, the two connections were the same size, so the plug could be inserted in either of two ways. This is unsafe, as plugging the neutral blade into the hot connection exposed people using metal fans, toasters and other appliances to a shock hazard.
  
  

Polarized Connection

• The later, polarized version of the NEMA 1-15 made the neutral connection wider. This means a polarized, two-blade plug can be inserted only the correct way, reducing the shock hazard. All electric appliances are now sold with the polarized plug.
  
  

NEMA 5-15

• The current standard outlet type, the NEMA 5-15, adds a third, round connection for a ground. This outlet also has the wider neutral connector. The spacing for hot and neutral connections is the same as for the 1-15 outlet, so you can use either two-blade or three-connector plugs in it. Smaller, well-insulated appliances use the two-blade plug; larger appliances such as washing machines and refrigerators have the grounded plug.
  
  

GFI

• A GFI outlet is a standard NEMA 5-15 outlet with an electronic detector built in. If the detector sees an imbalance between hot and neutral of five thousandths of an amp, it trips a switch that cuts the power. This prevents current from flowing through an improper path to ground, such as a person. GFI outlets are required in new home electrical outlets within 6 feet of a water source, such as a bathroom or kitchen.