Electrical Grounding 101

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  • Beginner

A fundamental aspect of electrical engineering, electrical grounding is the manner in which an electrical circuit is attached to the earth or the ground. The connection made with the earth is vital, for it uses the ground as a conductor. The earth is so comparatively large, any excess current traveling through a circuit is absorbed by dirt, water, rocks, and everything else that comprises it. In a real-world application, without a ground, a circuit would be potentially dangerous should an exposed metal part end up with a dangerous voltage in respect to ground, with current flowing through a grounded individual to complete its circuit.

How a Basic Circuit Works

Outlet box

A circuit is essentially a loop. Electrons in the form of current travel this loop. Various loads plugged into outlets or lights are connected to the circuit and receive power from it. Electrical current leaves the power source through the hot wire (in a home, the main circuit panel), travels to each receptacle, and returns through the neutral wire. Since the early 1960s, the code has required circuits to be properly grounded. In basic home circuits, this adds a third wire, the ground wire, that is there to ensure a return path for any current that is unable to complete its circuit. If there were only two wires (a hot and a neutral) connecting a light fixture to a circuit, the hot wire could end up inadvertently charging the metal box that contained it should a wire become loose. Simply changing the light bulb attached to it would be dangerous, for you would receive a shock through your body from the stored charge. You would become, in effect, the ground. In other words, the current, needing a place to go, would go through you to complete its circuit.

How a Grounding Wire Works

Spools of copper wire

To avoid this occurrence, every circuit is required to have a grounding wire attached to it. For safety purposes, grounding wires run the length of a home circuit and attach to every receptacle along the way, from light fixture to switch to the outlet. Should the wiring at any of those points become frayed or otherwise damaged, the individual ground would dispel any chance of electric shock. Of course, the grounding wire all links up and goes to the same place. At the point where electric power comes into your home, there is a grounding rod that is mostly buried in the ground. Ultimately, this is where excess current conducts. The main circuit panel is grounded, as is the power meter. The earth, then, is the final destination for any rogue current that is not safely contained in the circuit loop.

Electrical grounding is a basic principle of electrical engineering and home circuitry wiring, but it is also used to protect people and property from a lightning strike. Commonly called a lightning rod, it is really a grounding rod. Since lightning is an electrical charge in the air trying to complete its path to earth, the lightning rod provides the lightning bolt with the easiest path through which to complete its circuit back to earth, away from areas of the house that would otherwise absorb it. At sea, a boat must have a grounding rod to protect its instruments from shorting and to prevent the onboard metal from becoming conducive.

Although electrical grounding involves knowledge of circuitry, its basic definition is just what its name implies. By using the earth as a conductor of electricity, grounding ensures that metal devices, other conducting substances or, more importantly, people, do not become the path for current to escape.