Amperage is a term often used by electricians, and means electrical current, measured in amperes, or amps. The ampere is the SI unit for electrical current, or the amount of electrical charge that flows through a conductor in a given time. One ampere is a charge of one coulomb — about 6.241 X 1018 electrons — per second flowing past a given point. Electrical devices are rated according to their amperage, or the amount of current they typically draw from a mains supply when operating normally. When electricians speak of the electricity flowing in and out of a home, they may be referring to voltage, amperage or wattage depending on the circumstances, but when considering the effects of electric shock, it is the amperage, rather than the voltage, that is important.
Amps and Volts
Electricity is to home electrical circuits as water is to home plumbing systems. The voltage is roughly equivalent to the water pressure, and the amperage, or current, to the quantity of water that flows past a given point per second. At a given pressure, less water can get through a small pipe than a large one in a given time, so the size of the pipe can be regarded as equivalent to a measure of electrical resistance — a smaller pipe has higher resistance. The higher the electrical resistance of an appliance, the lower its current will be, and resistance is often dependent on the diameter of the wires.
Electricity is brought in to the home through power lines ultimately connected to a generator. To minimize energy loss through the resistance of the power lines, transformers are used to transmit the power at very high voltages. Before it reaches homes, however, additional transformers are used to reduce the voltage to a suitable value for domestic use, which is 110 volts in the USA, but 230 volts in Europe, for example. Voltage is a measurement of “potential” energy available, not necessarily how much is actually used.
This is where amperage comes in: an electrical appliance needs a certain amount of electrical energy to perform its job, and draws that amount of electricity from the “river” of volts in the line. A small device, such as 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 current ratings. A large electric motor may draw 100 amps of current, while a small heating element may draw only ten amps. Both tap into the same 110-volt line, but their current needs are noticeably different.
Watts are the units used to measure power consumption. A current of one amp at one volt uses one watt of power. The power used by a device is simply amps multiplied by volts, so an appliance rated at ten amps plugged in to a 110-volt supply will use 1,110 watts. Since watts are used by power companies to measure electricity consumed, and to charge customers, amperage is important in calculating the cost of running an electrical device. Typically, consumers will be charged by kilowatt-hours of power use — running a ten-amp device on a 110-volt supply for one hour will give a consumption of 1,110 watt-hours, or 1.11 kilowatt-hours.
The general rule of thumb for homeowners is the higher the current rating, 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 bills is a priority, then products with a lower amperage should be selected. If power and speed are more important, higher current rating products are generally best.
Amperage must be controlled in order to protect the electrical wires and circuits 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 current through circuit breaking. Larger electrical devices often have their own circuits with higher capacity fuses or breaker switches to avoid such overloads.
In the event of a person receiving an electric shock through carelessness or an electrical fault, it is the amount of current that flows through the body, and not the voltage, that determines the severity of the injuries caused, and the likelihood of a fatality. Many high school students will have experienced a shock of perhaps 50,000 volts from a Van de Graaf generator in the physics lab, but this produces an extremely small current, and is harmless. On the other hand, a 110-volt shock, with a current of just a small fraction of an amp, could well be fatal. A current of 0.1-0.2 amps flowing through a human body is usually lethal, due to its effects on the heart. Surprisingly, with prompt treatment, victims exposed to more than 0.2 amps may survive, as the severe muscle contractions induced can protect the heart from electrical interference.