What is Electrical Ground or Earth?
Electric ground, or earth in the U.K. and elsewhere, is the system of wiring a third wire in a circuit to carry away electrical current in the event of certain anomalies. Many modern devices now include a ground wire for safety reasons. While it does not eliminate the risk of electric shock, it does reduce the risk.
In a typical AC circuit one wire is designated as "hot". It has a ready supply of current to be drawn upon. A second wire called "common" or "neutral" completes the circuit and returns the current back to the service panel.
In this two wire scenario, if a fault occurs, such as a wire inside the device coming in contact with the housing, the user could complete a circuit to ground if they touch the housing. The electrical current could then travel through the hot wire, into the device, through the housing, through the user and into the ground. The result being an electric shock, possibly deadly, to the user.
To protect against this type of shock hazard, typically, the housing of a device is connected to a ground wire. This provides a "low-resistance" return path for electrical current. The key is that it be low-resistance. If the user had a lower resistance path to ground, then they would still receive a shock.
An often misunderstood element of the ground wire is that it actually carries current to the ground. In reality, most households are wired such that the ground wire and the common wire are joined together at the service panel. While most homes do have some sort of contact to ground, such as a ground rod or making use of plumbing pipes, the connection of ground to the common wire in the service panel is much more likely to carry and errant current.