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Last updated: August 6, 2019

What Does Ampere Mean?

An ampere (A), often shortened to “amp,” is a unit of measurement used to describe the strength of an electric current. A single amp represents a current flow rate of one coulomb per second through a circuit or other system. (A coulomb is a unit that describes the strength of an electric charge.) The ampere is one of the seven SI base units through which all other units of measurement are defined.

The ampere is an important concept in occupational health and safety practices related to electrical safety. It represents the amount of electrical charge that flows through a particular point over a specific duration, which makes it useful for describing the amount of energy to which a worker would be exposed if he or she came into direct or indirect contact with an energy source. A worker may die from exposure to 1/10th of an amp (current flow through his or her body) lasting only two seconds.

Safeopedia Explains Ampere

In the popular imagination, it is the amount of voltage in an electrical source that determines whether it is dangerous to humans. Modern electrical safety signs are marked with a lightning bolt and some version of the words “Danger: Electrical Hazard.” However, most people expect to see the words “Danger: High Voltage” instead. In truth, it is the electrical current—measured in amperes, not volts—that is most responsible for harm. While a certain voltage is necessary to move current through the body (due to the high resistance of dry skin), it is exposure to current that causes electric shock, and the severity of the shock depends on the magnitude of its current.

An understanding of the current-amps produced by an electrical system is also important for understanding the potential strength (measured in joules) of any arc flashes that system could produce. The strength of an arc flash is determined by the strength of the current (number of amps) produced in the event of a ground fault, as well as distance from the flash source and duration of exposure to the flash. According to OSHA, arc flashes are responsible for 80% of electrical injuries in the United States.

Between 2015 and 2016, 181 American workers experienced electrocution injuries, the majority of which were fatal. This high death rate underlines how exposure to only a small amount of current is sufficient to cause a fatality. At 1 milliamp (mA, one one-thousandth of an ampere), an individual will only feel a tingling sensation, but death becomes possible at 50-150 mA (likely at between 1.0 - 4.3 A) and is probable at 10 A. All major occupational safety authorities prescribe personal protective and training requirements to prevent worker exposure to harmful levels of current flow.


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