Chapter 5 - Electrical System Grounding and Bonding

Abstract

When working on electrical installations, the earth is one of the best safety devices. One may not think of the earth as a device, but when one ground electrical circuits to the earth, it provides protection by diverting dangerous current away into the ground. For this simple reason, in the language of electricians the term “ground” literally means earth. A “ground” is a conductive connection between an electrical circuit or a piece of equipment and the earth or another type of conductive material that is used in place of the earth. Both OSHA and the NEC have very specific requirements for utilizing grounding to reduce the risk of injury. The rationale for these requirements is simple—all electrical installations have to provide a means of transferring electrical current in the event of a circuit fault to reduce potential shock hazards. Grounding protects against shock hazards posed by fault currents. An electrical fault occurs when current flows through an abnormal or unintended path. For example, if the insulation in a conductor is damaged, the means of containing and directing the electrical current running through it will be compromised and ineffective. A fault current is several times greater than the current that normally flows through a circuit, because it is essentially electricity running wild instead of flowing in a controlled manner. Electricity always follows the path of least resistance, and that path could be you if a fault occurs within electrical equipment or components that have not been grounded.