Okay, I didn’t really do this, but there are plenty of people who have! This blog talks about electrical circuits and why some are 120-volts and others are 240-volt.
Electricity comes into houses through two “hot” wires. By convention, one is called black and one is called red, although in real life, both are often black. We also bring in a neutral wire, but it doesn’t carry any electricity into the house. It is a path back to the ground through the transformer at the street.
Houses have 240 volts available, and yet most of the household circuits are 120 volts. Each of the two hot wires coming into the house carries 120 volts. When we make a circuit from the black wire to the white wire, it creates a pressure of 120 volts. Additionally, a circuit from the red wire to the white wire also creates a pressure of 120 volts.
We can create a pressure of 240 volts by making a circuit between the black and red wires. Remember when we blogged awhile back about Tesla’s alternating circuits? The theory is in practice here with electricity. The two 120 volt wires alternate their current in a stable fashion and 240 volts is achieved.
So, if most household circuits run on 120 volts, why do we need the capability to pull 240 volts? It just depends on what you want to do. Most small household appliances are designed to run on 120 volts. Large appliances such as stoves, water heaters, and central air conditioners usually run on 240 volts. The larger pressure allows us to do more electrical work without large current flows. Although we could design these appliances to run on 120 volts, we’d have to use very large wires to safely carry the large currents. That is expensive and inefficient.
It boils down to what is most practical. In North America, we use the 120/240-volt system. In Great Britain, for example, they use a 240-volt system. Even their small appliances are designed to run on 240 volts, and all the circuits in their homes are wired for 240 volts. You probably know someone who’s traveled abroad and fried their hair dryer or electric razor. Now you know why!