Electricity and electrically operated devices are an integral part of our lives, and yet many of us have only a vague understanding of how electricity works. While virtually everyone uses amps, volts and watts every day, most of us don't know what these terms mean. But you don't need to be an electrical engineer to understand the basics.
What's a Watt?
A watt is a unit of power. Power is a measure of energy/time. A watt is equal to one joule (the basic unit of energy) per second. Any electrical device will draw a given number of watts, which will vary depending on the amount of power the device requires. A big electric saw will use more energy in a given period of time than a small hand-held drill. It requires more power and, therefore, has a higher wattage.
Amps and Volts
The most common analogy used in describing electricity is water current. You can think of voltage as water pressure. Amperage is akin to the amount of water flowing at that pressure. If you double the voltage but amperage remains fixed, twice as much electricity will move through the circuit in a given period of time. If you double the amperage, and the voltage remains the same, this will also double the amount of electricity that flows through in a given time interval. Either of these will double the power, which is energy per unit time, measured in watts.
Relationship between Watts, Amps and Volts
There is a simple relationship between watts, amps and volts. W=AV. That means the wattage is equal to the amperage times the voltage. In the U.S., voltage is approximately 120 volts for a standard electric outlet. This can vary, in a brownout, for example, in which a you experience reduction in the voltage supplied to households. If this occurs, an electric device will draw more amps in order to maintain the same power. This is one of the reasons circuit breakers exist: A tool, or the circuit that supplies the power, drawing more amps than it is designed for can overheat and present a fire hazard.
Watts Remain the Same
Most countries use a standard of 220 volts for electric outlets. The United States uses 120 volts. If you want to use your American-made electric devices in other countries, you'll need an adapter to reduce the voltage. But a tool designed for the American market will use the same number of watts as a non-American one. The amount of power required to make a drill do its job will not change from one country to another. So, since the voltage is lower in the U.S., the amperage will be higher. The wattage will remain approximately the same.
Wattages for Common Power Tools
Below are the most commonly used power tools with their typical amperage, based on the American standard of 120 volts, and the corresponding wattage. Remember that the wattage will be approximately the same outside the U.S., but the voltage will be higher, and the amperage lower.
Circular Saw: 12-15 amps / 1440 to1800 watts
Jigsaw: 4.5 -- 7 amps / 540 to 840 Watts
Reciprocating saw: 4- 12 amps / 480 to1440 watts
Hand-held drill 3.5 amps / 420 watts
Drill press: 4 to 12 amps / 480 to 1440 watts
Orbital disk sander: 3 to 4 amps / 360 to 480 watts
Router: 6 to 12 amps / 720 to 1440 watts
Table saw: 15 amp / 1800 watts
Bench grinder: 2 to 6 amps / 240 to 720 watts
Small angle grinder: 7 to 10 amps / 840 to 1200 watts
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