No, houses do not typically have DC current. The electricity that powers homes and businesses in the United States and many other countries is AC (alternating current). DC (direct current) electricity is used in some applications, but the power that comes from electric utilities to homes and businesses is AC.
AC vs DC Current
AC and DC refer to two different types of electrical current:
- AC stands for alternating current. The current switches direction back and forth periodically. AC electricity allows voltage to be increased or decreased easily with transformers. This allows efficient transmission over long distances.
- DC stands for direct current. The current flows in one constant direction. Batteries provide DC electricity. So do solar panels, fuel cells, and car alternators.
Here are some key differences between AC and DC current:
| AC (Alternating Current) | DC (Direct Current) |
|---|---|
| Periodically reverses direction | Flows in one direction |
| Used for power transmission and in homes/businesses | Used in batteries, solar panels, cars |
| Can be stepped up/down in voltage with transformer | Voltage cannot easily be changed |
As you can see, AC and DC have quite different characteristics. Next we’ll look at why AC is used for powering buildings.
Why Houses Use AC Instead of DC
When electricity generation and distribution systems were first being developed in the late 1800s and early 1900s, there was a well-known battle between Thomas Edison and Nikola Tesla and George Westinghouse.
Edison and DC Power
Thomas Edison championed the use of DC for electricity distribution. At the time, electricity generation was done locally using DC generators rather than centrally with AC generators. Edison came up with a DC power distribution system to bring power to homes and businesses near his Pearl Street generating station in Manhattan in 1882.
Tesla, Westinghouse and AC Power
Nikola Tesla and George Westinghouse believed that AC was better for power transmission over long distances. Tesla invented the AC induction motor and transformer, allowing efficient transmission and stepping voltage up and down.
Westinghouse acquired Tesla’s patents and promoted AC distribution instead of Edison’s DC system. AC could be transmitted over much greater distances than DC and allows for easy voltage conversion.
AC System Wins Out
By the early 1900s, AC became the favored method for generating and transmitting electricity. Westinghouse and Tesla won the “War of the Currents” over Edison’s DC system. AC allowed centralized generation at power plants using efficient AC generators. The voltage could be stepped up for efficient transmission over long distances. Then it could be stepped back down for safe use in homes and businesses.
Here are some key reasons why AC became dominant over DC for power systems:
- AC voltage can be easily increased or decreased with a transformer. This allows long distance transmission at high voltage.
- AC generators, motors and other equipment were technologically superior to early DC versions.
- AC allowed for universal standards to be set for voltage and frequency across large areas.
- Central AC generator plants had economies of scale over small local DC generators.
This AC system became known as the electrical grid that we still use today. The grid delivers AC power to homes, businesses, schools, factories, and everywhere else that needs electricity.
When DC Electricity Is Used
While AC provides the vast majority of our electricity, DC is still used in some applications:
Batteries and Portable Devices
All batteries provide DC power. This allows portable electronics like laptops, phones, flashlights and more to be used anywhere. Batteries are charged using AC power from the grid, which is then converted to DC.
Vehicles
Cars, trucks, buses and other vehicles mostly run on DC power. The alternator charges the battery and electrical system at 12 or 24 volts DC. Hybrid and electric vehicles have larger battery packs providing 300+ volts DC.
Solar PV Systems
Photovoltaic solar panels generate DC electricity when exposed to sunlight. This allows solar to charge batteries, power DC appliances, or be inverted to AC for use in a building.
Backup Power Supplies
Uninterruptable power supply (UPS) systems provide backup DC power from batteries in the event of blackouts. The DC can power critical equipment like computers until AC power is restored.
Electronics
Many electronic devices and circuits run on low voltage DC provided by AC adapters or batteries. DC-DC converters are used to step-up or step-down the DC voltage as needed.
HVDC Transmission
While AC dominates long distance transmission, high voltage DC (HVDC) lines are occasionally used for efficiency over extremely long distances. Undersea cables also utilize HVDC.
So in summary, while our wall outlets provide AC power to homes and buildings, DC electricity still plays an important role in many applications. Both AC and DC have their advantages, and modern electrical systems utilize both forms extremely well.
Conclusion
Houses do not have DC current. The electricity delivered over the electrical grid to homes and businesses is AC power. However, DC power is still used in many devices and applications through batteries, solar panels, vehicles, electronics, and HVDC transmission lines. The “War of the Currents” over 100 years ago settled the AC vs DC debate in favor of AC for power distribution. This allows homes and businesses to enjoy the many benefits of AC electrical service.
