What Are The Electric Points In Usa?

This article provides an overview of the types of electrical outlets and plugs used in the United States. Understanding the different plug types and shapes, voltages, and safety features can help homeowners better utilize and safely interact with the electrical system in their houses. We’ll cover the history and evolution of electrical systems in American homes, the standard outlet types and shapes, voltage and frequency, and safety mechanisms built into the outlets. Smart outlets and other specialty outlets will also be discussed. By the end, readers will have a deeper understanding of the standardized electrical system in the US and how to use it effectively in their homes.

History of Electricity in the US

The development of electricity in the United States began in the late 19th century with the commercialization of electric lighting and the invention of the electric motor. Early electrical systems used direct current (DC) transmitted over short distances. The invention of the transformer enabled the use of alternating current (AC) for long distance transmission. The “war of the currents” between DC and AC systems eventually led to AC becoming the standard for generating and transmitting electricity.

The earliest electrical outlets and plugs date back to the 1880s and were very simple designs intended for lighting. Some of the earliest plugs had just two flat metal contacts on the male end and screw-terminal connections on the female end. These basic plugs and outlets eventually evolved into more complex designs with multiple contacts for handling higher voltages needed for appliances and electric motors. The early systems were also very unsafe with exposed contacts that could deliver dangerous shocks.

During the early 20th century, standardized plug and outlet designs started emerging, like the parallel blade “Type A” plug. Safety features also improved with the development of polarized and grounded plugs. This helped pave the way for electricity to be adopted in American homes and businesses for lighting, appliances, and power tools.

Common Household Plug Types

Most electric plugs used in homes and businesses in the United States follow standards set by NEMA, the National Electrical Manufacturers Association. The most common plug types are:

  • NEMA 1 – Two parallel flat blades, no grounding pin. Used for small appliances like lamps, radios, and phone chargers.
  • NEMA 5-15 – Two flat parallel blades and a round grounding pin below. Used for most 120V household outlets. Referred to as a 2-prong (no ground) or 3-prong (with ground) plug.
  • NEMA 5-20 – Similar to NEMA 5-15 but with one vertical blade turned 90 degrees. Used for 20 amp appliances like large air conditioners.
  • NEMA 6-15 – Two flat blades at an angle and a round ground pin below. Used for 240V appliances like clothes dryers.
  • NEMA 6-20 – Similar to NEMA 6-15 but with a T-shaped neutral blade instead of flat. Used for heavy 240V appliances.
  • NEMA 10-30 – Two flat blades, a U-shaped neutral, and round ground pin. Used for old 240V stove/oven outlets.

The most common is the NEMA 5-15 which comes in 2-prong and 3-prong versions. 3-prong is considered safer as it grounds the appliance to prevent electric shock in case of malfunction. Building codes now require 3-prong grounded outlets in most new construction.

Polarized and Grounded Plugs

Polarized plugs have one prong that is wider than the other, which allows the plug to be inserted into an outlet only one way. The purpose of polarization is to prevent electric shock. Polarized plugs ensure that the current travels in the correct direction through electrical devices.

The wider prong on the plug connects to the wider slot on the outlet, which is neutrally charged. The narrower prong connects to the “hot” side that carries electricity. If the plug were to be reversed, the “hot” and neutral connections would be flipped, which could damage appliances and potentially cause shocks. Polarization ensures the plug can only go in the correct way.

Grounded plugs have a third prong below the two vertical prongs. This third prong connects the appliance to ground, providing a safe path for excess electric charges to flow to the ground instead of through a person’s body. Grounding protects people from electrical shock in the event of a short circuit or other malfunction.

Outlet Shapes and Orientations

There are several standard outlet shapes and orientations used for residential and commercial wiring in the United States. These standards are defined by NEMA (National Electrical Manufacturers Association) for plugs, receptacles, and connectors.

The most common NEMA outlet is NEMA 5-15 which has two vertical slots for the two poles (line and neutral) and a round grounding hole below. There are also NEMA 5-20 outlets which add a horizontal slot for 20 amps instead of 15 amps. For special 240 volt circuits like stoves and dryers, NEMA 6-15 and NEMA 6-20 use a T-shaped slot instead.

NEMA 10-30 and 14-30 are high-amperage configurations used for electric ranges and dryers. They have angled neutral and hot slots along with a U-shaped grounding slot. These are often installed vertically to differentiate them from typical household outlets.

For commercial and industrial wiring, NEMA L-series outlets like L5-15 and L6-20 utilize twist-locking connectors instead of typical slots. This prevents cords from vibrating loose.

The orientation of outlets also provides visual cues about the circuit type. Most standard outlets are installed with the ground prong down. However outlets with the ground prong facing up indicate they are controlled by a wall switch. Upside down outlets are also sometimes used to indicate a 240 volt circuit.

Voltage and Frequency

The standard voltage and frequency of electricity in the United States is 120 volts at 60Hz (hertz, or cycles per second). This means that the electrical outlets in American homes supply electricity at 120 volts, and the current alternates direction 60 times per second.

The 120 volt standard was established in North America in the late 19th century by Thomas Edison as part of his effort to establish safe and widespread electrical service through direct current. However, as alternating current, championed by Nikola Tesla and George Westinghouse, became prevalent in the early 20th century, the standard voltage was kept at 120V for compatibility but the frequency was changed to 60Hz.

This 120V/60Hz system provides a good balance between safety and transmission efficiency for residential and commercial use. Higher voltages like 240V are more efficient for transmitting large amounts of power over long distances, which is why they are used for high power applications like clothes dryers or electric ranges. But 120V minimizes the risk of dangerous electrical shocks while still providing adequate power for most home and office devices.

The 60Hz frequency was chosen partly for convenience based on existing AC generators designed to run at that speed. But there are also technical reasons why 60Hz works well – higher frequencies can cause inductive losses in motors while lower frequencies can cause issues like flickering lights.

So the 120V/60Hz system became the standard for the US electric grid and allows compatible devices to be plugged in anywhere in the country. Though large appliances may require 240V, regular outlets supply 120V/60Hz power to meet most home electricity needs safely and efficiently.

Safety Features

Electricity can be dangerous, so outlets and plugs in the US contain safety features to prevent electrocution and fires. Some key safety features include:


Outlet covers are plastic shutters that block access to the slots when nothing is plugged in. This prevents kids from sticking fingers or objects into the sockets. The shutters only open when equal pressure is applied to both shutters, like when inserting a plug.

Tamper Resistance

Tamper resistant (TR) outlets have a built-in shutter system to prevent inserting foreign objects into the slots. The shutters won’t open unless the proper prongs of a plug press them down at the same time. TR outlets are now required in all new home construction in the US.

GFCI Protection

A GFCI (ground fault circuit interrupter) outlet monitors electricity flow and detects dangerous “leaks.” If it senses a problem, it cuts off power in as little as 1/40th of a second to prevent shock. GFCIs are required in bathrooms, kitchens, basements, garages and other areas at risk of electric shock.

Special Outlets

In addition to standard household outlets, there are some special outlet types designed for specific purposes:

Weatherproof Outlets

Weatherproof outlets are designed for outdoor use. They feature covers that seal over the outlet when it’s not in use, protecting it from moisture, dirt, and debris. The outlets themselves are also sealed to prevent water from getting inside.

Tamper Resistant Outlets

Tamper resistant outlets have a built-in shutter system that prevents foreign objects from being inserted into the slots. This helps protect children from sticking items like paperclips into the outlet which could cause electric shocks and burns.

Timer Outlets

Timer outlets allow you to program an outlet to turn on and off at set times. This allows you to control lamps, holiday lights, and other plugged in devices automatically at scheduled times.

Smart Outlets

In recent years, smart outlets have become increasingly popular in the United States. Smart outlets allow users to control and monitor devices plugged into them using a smartphone app or voice control through a virtual assistant like Amazon Alexa or Google Assistant. Some of the key features of smart outlets include:

Remote Control

Smart outlets can be turned on or off remotely using an app on your phone, even if you’re away from home. This allows you to control devices plugged into the smart outlet from anywhere. For example, you can turn on a lamp or small appliance before arriving home.

Energy Monitoring

Many smart outlets have built-in energy monitoring that tracks how much electricity a plugged-in device is using. This allows you to identify high energy-consumption devices and adjust usage to be more energy efficient. The app will display real-time energy usage and some outlets even allow you to set budgets and get alerts.

With their advanced connectivity and monitoring capabilities, smart outlets are becoming a staple in many modern American homes. They provide added convenience, security, and energy savings.


In summary, the US has standardized on 120V electricity at 60Hz frequency. The most common plug types are two-prong polarized NEMA 1, three-prong grounded NEMA 5, and NEMA 14 for special equipment. Outlet orientation and shape also follows standards, with vertical slots for 120V and horizontal slots for 240V. Safety has improved over the years with the addition of ground pins, safety shutters, and GFCI outlets near water. While the core standards remain consistent, new smart outlets and USB charging ports have also emerged. Overall, standardization of the electrical system in the US has provided compatibility, safety, and reliability for consumers.

Adhering to electrical standards is crucial for protecting consumers. The established standards ensure that electrical devices and outlets are compatible throughout the country. They also incorporate important safety features to prevent electrocution and fires. As electricity is an essential utility in every home and business, maintaining uniform standards allows the electrical grid and devices to work seamlessly and safely across the nation.

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