How Does Electricity Work in the Home?

Understanding Volts, Amps, and Watts

Construction worker looking at electrical wires

Mikael Vaisanen / Getty Images

Household electricity and its current flow can seem quite mysterious, since this electromagnetic force is entirely invisible. But it can be easier to understand if you compare it to water flowing through the plumbing pipes in your home. Although the analogy is not perfect, there are striking similarities in how these systems work.

Both water and electricity enter your home from the utility service lines and exit after being distributed throughout the house. Water flows through pipes and is used at faucets and other fixtures before existing via a drain system. Electricity flows through a network of wiring and is used by lights, appliances and other electrical devices; it, too, then "exits" the home by flowing back to ground.

Pressure Makes It Flow

Water flows throughout a home's supply piping because it is pressurized by the water company or by a well system. Once it is used at a fixture, it no longer has pressure and must rely on gravity to flow through the drain pipes. Therefore, all the water exiting the house through drains can be considered to have no pressure. Likewise, electricity has a specific pressure (voltage) that is regulated by the power company. This pressure allows the electrical current to flow through the wiring leading into the house and throughout the home's electrical system. Electricity is used by each electrical device or appliance. Anything unused returns to the electrical service entry point (and ultimately back onto the power grid) via neutral circuit wires. This return is considered to be without pressure, much like water going down the drains of your home.

Pressure = Voltage

Increasing water pressure in a plumbing pipe means the water flows through with greater force. The same is true with electrical wiring; more pressure means greater force. While water pressure is measured in pounds per square inch or psi, electrical pressure is measured in volts or voltage. All electrical devices are rated for specific voltages. Most devices and small appliances in a home are rated for about 120 volts, while high-voltage appliances, such as electric dryers, ranges, and many baseboard heaters, are rated for about 240 volts.

Flow = Amperage

Just as larger water pipes carry more flow, or a higher volume, of water, larger electrical wires can carry more electrical current. Electrical current is measured in amps or amperage. Along with voltage, all electrical components are rated for safe amperage levels. The circuit breakers in your home's breaker box each control the electrical flow in a separate circuit, and each has a specific amp ratings. Most general-use circuits are rated for 15 or 20 amps, while large-appliance circuits are rated for 30, 40, 50 or more amps. When you power too many appliances or lights by one circuit, you're effectively increasing the flow to the point of overload. This causes the breaker to trip and shut off the power to the circuit.

Voltage x Amperage = Watts

A watt is a measure of how much electricity is used by the electrical devices drawing power from a circuit. Watts are a function of both voltage (pressure) and amperage (flow, or current). Multiplying voltage and amperage gives the wattage.

For example, your microwave oven might be rated for a maximum of 10 amps, and it is plugged it into a 120-volt outlet. The maximum power draw of this appliance therefore, is 10 (amps) x 120 (volts) = 1,200 watts. That's how much electricity the microwave is using whenever it's running on high (other settings, like defrost, probably use fewer watts). In similar fashion, you can compute the available wattage of an entire circuit. A 15-amp, 120-volt household circuit has a maximum of 1,800 watts available (15 x 120). This means that all the light fixtures and plug-in appliances running at the same time can add up to no more than 1,800 watts before it overloads the circuits and trips a circuit breaker.

Conserving Electricity

As with water, where conservation means reducing the number of gallons consumed, conserving electricity is a matter of reducing the total amount of wattage consumed. Returning to our plumbing comparison, an energy-efficient light bulb can be likened to a low-flow shower head. Old shower heads had flows of 5 gallons per minute, but today's low-flow models use no more than 2.5 gallons per minute. Similarly, , where we once routinely used 60-watt incandescent bulbs, we now use may use 12- or 14-watt LED bulbs. And just as water use can be reduced by fixing faucets that leak, electrical consumption can be reduced by shutting off lights and appliances when you leave a room.

Conservation of energy, like conservation of water, involves reducing the quantity of electricity consumed, as measured in watts. This can be accomplished by using more efficient light bulbs and appliances that have lower wattage needs, or by limiting the time they are drawing power (such as by not running air conditioning constantly).