Basic Electrical Concepts
Current is the flow of electrical energy. It flows through a wire similar to the way water flows through a hose. A small stream of water can flow easily through a small hose, while larger flows require larger hoses. The same is true for electrical current. A small amount of current can be carried by a thin wire, but a large amount of current requires heavier wire. Current is measured in amperes, often called amps.
Voltage is electrical pressure that causes current to flow. Voltage is measured in units called volts. Voltage pushes current through a wire the same way pressure pushes water through a hose. A wire connected to a voltage source is said to be energized or hot. However, there must be enough voltage to overcome the wire’s electrical resistance before current will flow.
Resistance is the opposition that a material presents to the flow of current. It is measured in units called ohms. Current can be passed easily through some materials. Copper wire, for example, has low electrical resistance, so current flows through it easily. A material that current can flow through easily is called a conductor. Other materials, such as rubber, have high electrical resistance and are called insulators. Current cannot easily flow through an insulator.
Electrical shock is the body’s physical reaction to a significant amount of current flowing through it. The severity of the shock depends on several factors. Three main factors are the amount of current flowing through the body, the length of time that the current flows and the path that the current takes.
1. Amount of current: The more current there is flowing through the body, the stronger and more dangerous the shock. The lighting and equipment circuits at construction sites, service buildings, substations, and transmission and distribution lines carry more than enough current to produce a fatal shock.
2. Amount of time: Even a relatively small amount of current flowing for a long enough period of time can seriously injure or even kill a shock victim. The more time the body has current flowing through it, the more severe the shock.
3. Current path: The third shock severity factor is the path that the current takes through the body. It is important to note that current will only flow if there is a complete path to follow.
• If a person touches an energized conductor with one hand and another part of the same circuit with another part of his or her body, the person becomes part of the circuit. In other words, a complete path for current flow is provided, and the person will receive a shock.
• The path that current takes through a person’s body can affect the severity of a shock because some parts of the body are more vulnerable to the effects of current flow than others.
• A relatively small amount of current flow through the heart is more dangerous than a larger amount of current flow that does not pass through the heart.
• In general, current will flow through all available paths, but most of the current will flow through the path of least resistance.
Different amounts of current have different effects on the human body, and the severity of these effects increases as the level of current increases. A very small amount of current may cause only a slight tingling sensation. Increased amounts of current can cause increasing pain; loss of muscle control; breathing difficulties; ventricular fibrillation, which is uncontrolled vibration of the heart muscle; and eventually death.
The most frightening aspect of these effects is that even the most severe bodily effect can be caused by current values that are much less than half an amp, and electrical equipment is often capable of supplying hundreds or thousands of amps.
About the Author: John Boyle is vice president of safety and quality for INTREN, an electric, gas and telecommunication construction company based in Union, Ill. Boyle has more than 28 years of experience, and has worked in nuclear and wind power generation and electric and gas distribution.