The type of electrical current used in homes is Alternating Current (AC). AC is the standard electrical power for nearly all residential and commercial buildings globally. While the fundamental principles of AC are consistent, technical specifications vary geographically. In North America, the standard operates at 60 Hertz and a nominal voltage of 120 volts. This system was adopted due to AC’s efficient distribution capabilities over long distances.
Understanding Alternating Current
Alternating Current is defined by the periodic reversal of the electron flow’s direction within a conductor. Unlike Direct Current (DC), which maintains a constant, one-way flow, AC oscillates back and forth from positive to negative polarity. This constant change creates a sinusoidal waveform, which is the typical shape of the power supplied to homes.
The speed of this directional change is quantified by frequency, measured in Hertz (Hz). One Hertz represents one complete cycle—a full oscillation from one direction to the opposite and back—occurring every second. In North America, the standardized frequency is 60 Hz, meaning the current completes 60 full cycles per second.
Residential Power Specifications
North American residential power is standardized at a nominal voltage of 120 volts and a frequency of 60 Hertz. This 120-volt supply is routed to standard wall outlets for lighting and most smaller appliances. Voltage represents the electrical potential difference that drives the current.
A higher voltage of 240 volts is also supplied to the residence for larger, high-power appliances. Dedicated circuits power devices like electric clothes dryers, ovens, and central air conditioning units, which require more energy. The consistent 60 Hz frequency is maintained across both voltage levels, ensuring frequency-dependent equipment functions as designed.
The Efficiency Advantage of AC
AC was adopted as the standard for residential power due to its superior efficiency for long-distance transmission. Power loss during transmission is related to the current squared, meaning high current levels lead to significant energy waste. AC allows for the manipulation of voltage levels to minimize this loss.
The transformer is a passive electrical device that works only with AC, enabling the voltage to be easily increased or decreased. Utilities use transformers to “step up” the voltage to hundreds of thousands of volts for transmission, which dramatically lowers the current and minimizes power loss. The voltage is then “stepped down” multiple times until it reaches a safe, usable level for homes. This flexibility is a capability that Direct Current systems lacked, making AC the favored choice for wide-scale power distribution.
Power Delivery to the Home
The current’s journey begins after traveling through high-voltage transmission lines and being processed at a substation. It moves through distribution lines to a local neighborhood. A final distribution transformer, typically mounted on a utility pole or ground pad, performs the final step-down. This reduces the medium-voltage line power to the 120/240-volt level required by the home.
The power then travels via a service drop, connecting the utility equipment to the house. Next, the current passes through the electric meter, which records the household’s energy consumption for billing. Finally, the power enters the main breaker panel (service panel or load center). This panel serves as the central entry point, safely dividing the incoming power into individual circuits that run throughout the home.