Amperage, also called current, is the amount of electrical energy flowing through an appliance at any given time. This measurement is expressed in units called amperes, often shortened to amps. When electricians speak of the electricity flowing in and out of your home, they may be referring to voltage, amperage or wattage depending on the circumstances. Of the three, amperage is the one you may experience first when you plug in a faulty lamp or flip the wrong switch.

Understanding amperage may require a crash course in electrical engineering, wiseGEEK style. Electricity is to home electrical circuits as water is to home plumbing systems. Electricity is brought in to the home through power lines ultimately connected to a generator. In a standard US home system, this incoming electricity is limited to 110 volts. In other countries, it may be closer to 230 volts. Voltage is roughly the equivalent of how much water can fit in a pipe. Volts don't flow by themselves -- they are drawn from a high point (the line outside the house) to a low point (the toaster) once the circuit is completed by the toaster's switch. Voltage is mostly a measurement of 'potential' energy available, not necessarily how much is actually used.

This is where amperage comes in. The toaster, or any other electrical product, needs a certain amount of electrical energy to perform its job. It draws that amount of electricity from the 'river' of volts in the line. A small electrical appliance like a toaster usually needs less power than a larger appliance such as a refrigerator or power saw. In electrical terms, these appliances work at different amperage rates. A large electric motor may draw 100 amps, while a small heating element may draw only 10 amps. Both tap into the same 110 voltage line, but their amperage needs are noticeably different.

Amperage must be controlled in order to protect the electrical lines from overheating or short-circuiting. This is why electricians use fuses and breakers. A 30 amp fuse, for example, will allow smaller appliances to run on the line it protects, but if an electric clothes dryer pulls 60 amps, a metal filament in the fuse will melt and break the circuit immediately. Breaker switches also control amperage through circuit breaking. Larger electrical devices often have their own circuits with higher capacity fuses or breaker switches to avoid such overloads.

The general rule of thumb for homeowners is the higher the amperage, the more an appliance will cost to run. There is always a trade-off between power and economy when it comes to electrical devices. If economizing on the monthly utility is a priority, then select products with lower amperage. If power and speed are important, then look for products with higher amperage. The utility company bills customers based on total wattage used, which is calculated by multiplying amperage by voltage. Wattage is the basic measuring unit of electrical power, so customers are usually charged by the watt or kilowatt. This is why it is important to turn off electrical devices when they are not needed. Extra amperage means a higher amount of billable wattage hours.