Every country has different rules regarding distribution of electricity for appliances and lighting. International Electrotechnical Commission (IEC) publishes the standard of voltage, frequency and plug types for domestic appliances. According to IEC, following standard of voltage and frequency is maintained in USA.

CountryPlug TypePlug StandardResidential VoltageFrequency
United States of America (USA)A, B* NEMA 1-15P

* NEMA 5-15P

Plug Type

Type A and Type B are used in Central and North America. The Type A electrical plug (or flat blade attachment plug) is an ungrounded plug with two flat parallel pins. The Type B electrical plug has two flat parallel pins and a round grounding (or earth) pin. The earth pin is longer than the other two so that the device is grounded before the power is connected. Type B plugs are rated at 15 amps.

A_3d_plug_l Plug Type A

B_3d_plug_l Plug Type B

The pins on Type A and Type B plugs have a hole near the tip that fits into ‘bumps’ found on the contact wipers of some sockets, so that the pins are gripped more tightly allowing for better contact and also to prevent the plug from slipping out of the socket. Some sockets have spring-action blades that grip the sides of the pins, making the holes obsolete.

Plug TypesPin NumberGroundingAmp RatingVoltage RatingSocket
Type A2 pinsNot grounded15A100-127VSocket compatible with type A
Type B3 pinsGrounded15A100-127Socket compatible with type A and type B

Plug Standard

Standards of Power plugs and receptacles used in USA are set by National Electrical Manufacturers Association (NEMA).  In USA, NEMA 1-15 P and NEMA 5-15 P standards are used. According to NEMA nomenclature, NEMA 1 devices are two wire non-grounding devices rated for 125V maximum.  NEMA 1-15P plugs have two parallel flat blades, 14 inch (6.35 mm) wide, 0.06 inches (1.524 mm) thick, 582332 inch (15.875–18.256 mm) long, and spaced 12 inch (12.7 mm) apart.

All NEMA 5 devices are three-wire grounding devices (hot-neutral-ground) rated for 125 V maximum, with the 5–15, 5–20 and 5–30 being grounded versions of the 1–15, 1–20 and 1–30, respectively. The addition is a 316-inch (4.763 mm) diameter round or U-shaped ground pin, 18 in (3.175 mm) longer than the power blades (so the device is grounded before the power is connected) and located below them by 14 in (6.35 mm) edge-to-edge or 1532 in (11.91 mm) center-to-center.


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