4.2: The Basics of Electricity

Operating an electrical switch is like turning on a water faucet. Behind the faucet (or switch) there is a source of water (or electricity), a way to transport it, and pressure to make it flow. The faucet's water source is a reservoir or pumping station. A pump provides enough pressure for the water to flow through the pipes. The switch's electrical source is a power generating station. A generator provides the pressure (voltage) for the electrical current to travel through electrical conductors, or wires.

Electricity is the flow of an atom’s electrons through a conductor; caused by a force (voltage) placed on the conductor. Electrons are the outer particles of an atom that contain a negative charge. When electrons flow through a conductor, the flow is called electric current. Electricity is produced in a generating plant. When electricity leaves a power plant, its voltage is increased in order to transmit it over long distances. The high-voltage power travels along transmission lines to a substation, then distributed through more lines to service drops that step down the voltage to levels between 240 and 480 volts. Voltage is the fundamental force or pressure that causes electricity to flow through a conductor and is measured in volts (V). Voltage is synonymous with electrical pressure. The more voltage present, the more force or pressure is pushing the electricity. An overhead power line uses high voltage (thousands of volts) to carry electricity over large distances, from generating stations to our communities and then to our homes and businesses.

Current is the flow of electrons from a source of voltage through a conductor and is measured in amperes (Amps). If the current flows back and forth (a cycle) through a conductor, it is called alternating current (AC). In each cycle the electrons flow first in one direction, then the other. In the United States, the normal rate is 60 cycles per second [or 60 Hertz (Hz)]. If current flows in one direction only (battery operated/cordless tools), it is called direct current (DC).

AC is most widely used because it is possible to step up or step down (i.e., increase or decrease) the voltage through a transformer. For example, when voltage from an overhead power line is run through a pole-mounted transformer, it can be stepped down to normal household voltage. Resistance is anything that impedes (blocks) the flow of electricity through a conductor and is measured in Ohms.

The term "ground" refers to a conductive body, usually the earth. "Grounding" a tool or electrical system means intentionally creating a low-resistance path to the earth. When properly done, current from a short or from lightning follows this path, thus preventing the buildup of voltages that would otherwise result in electrical shock, injury and even death.

An Arc Flash Hazard is defined as a source of possible injury or damage to health associated with the release of energy caused by an electric arc. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur. Arc flash can be caused by dust, dropping tools, accidental touching, condensation, material failure, corrosion, and faulty installation. Three factors determine the severity of an arc flash injury: proximity of the worker to the hazard, temperature, time for circuit to break. Typical results from an arc flash include: burns (Non-FR clothing can burn onto skin), fire (could spread rapidly through building), flying objects (often molten metal), blast pressure (upwards of 2000 lbs./ft²), sound blast (noise can reach 140 dB – as loud as a handgun), and heat (upwards of 35,000 degrees F).