|  | 4.1 | Basics of Electricity
| 4.1.9 | Purpose of grounding networking equipment
For AC and DC electrical systems, the flow of electrons is always from a negatively charged source to a positively charged source. However, for the controlled flow of electrons to occur, a complete circuit is required. Generally speaking, electrical current follows the path of least resistance. Because metals such as copper provide little resistance, they are frequently used as conductors for electrical current. Conversely, materials such as glass, rubber, and plastic provide more resistance. Therefore, they do not make good electrical conductors. Instead, these materials are frequently used as insulators. They are used on conductors to prevent shock, fires, and short circuits. Electrical power is usually delivered to a pole-mounted transformer. The transformer reduces the high voltages, used in the transmission, to the 120 or 240 volts used by typical consumer electrical appliances. Figure shows a familiar object, electricity as supplied through wall outlets in the US (other nations have different wall outlet configurations). The top two connectors supply power. The round connector on the bottom protects people and equipment from shocks and short circuits. This connector is called the safety ground connection. In electrical equipment where this is used, the safety ground wire is connected to any exposed metal part of the equipment. The motherboards and computing circuits in computing equipment are electrically connected to the chassis. This also connects them to the safety grounding wire, which is used to dissipate static electricity. The purpose of connecting the safety ground to exposed metal parts of the computing equipment is to prevent such metal parts from becoming energized with a hazardous voltage resulting from a wiring fault inside the device. An accidental connection between the hot wire and the chassis is an example of a wiring fault that could occur in a network device. If such a fault were to occur, the safety ground wire connected to the device would serve as a low resistance path to the earth ground. The safety ground connection provides a lower resistance path than your body. When properly installed, the low resistance path, provided by the safety ground wire, offers sufficiently low resistance and current carrying capacity to prevent the build up of hazardously high voltages. The circuit links directly to the hot connection to the earth. Whenever an electrical current is passed through this path into the ground, it causes protective devices such as circuit breakers and Ground Fault Circuit Interrupters (GFCIs) to activate. By interrupting the circuit, circuit breakers and GFCIs stop the flow of electrons, and reduce the hazard of electrical shock. The circuit breakers protect you and your house wiring, but further protection - often in the form of surge suppressors and Uninterrupted Power Supplies (UPS) - are required to protect computing and networking equipment.