The Filipino Electrical Engineer

IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems

The objectives of electrical system protection and coordination are to prevent injury to personnel, to minimize damage to the system components, and to limit the extent and duration of service interruption whenever equipment failure, human error, or adverse natural events occur on any portion of the system. The circumstances causing system malfunction are usually unpredictable, though sound design and preventive maintenance can reduce the likelihood of their happening. The electrical system, therefore, should be designed and maintained in such a way as to protect itself automatically.

Prevention of human injury is the most important objective of electrical system protection. Interrupting devices should have adequate interrupting capability and energized parts should be sufficiently enclosed or isolated so as not to expose personnel to explosion, fire, arcing, or shock. Safety has priority over service continuity, equipment damage, or economics.

These fundamental principles of safety have always been adhered to by responsible engineers engaged in the design and operation of electrical systems. ANSI/NFPA 70-1984 [4]1 (National Electrical Code [NEC]) and state and local codes have prescribed practices intended to enhance the safety of electrical systems. In recent years an increased concern about safety has led to many studies resulting in detailed recommendations and regulations relating to electrical systems. Prominent among these are the regulations of the Occupational Safety and Health Administration (OSHA) of the United States Department of Labor. Engineers engaged in the design and operation of electrical system protection should familiarize themselves with the most recent OSHA regulations and all other applicable codes and regulations relating to human safety.

Abstract : The problems of system grounding, that is, connection to ground of neutral, of the corner of the delta, or of the midtap of one phase, are covered. The advantages and disadvantages of grounded vs. ungrounded systems are discussed. Information is given on how to ground the system, where the system should be grounded, and how to select equipment for the ground of the neutral circuits. Connecting the frames and enclosures of electric apparatus, such as motors, switchgear, transformers, buses, cables, conduits, building frames, and portable equipment, to a ground system is addressed. The fundamentals of making the interconnection of a ground conductor system between electric equipment and the ground rods, water pipes, etc., are outlined. The problems of static electricity— how it is generated, what processes may produce it, how it is measured, and what should be done to prevent its generation or to drain the static charges to earth to prevent sparking—are treated. Methods of protecting structures against the effects of lightning are also covered. Obtaining a low-resistance connection to earth, use of ground rods, connections to water pipes, etc., are discussed. A separate chapter on electronic equipment is included.

Keywords: connection to earth, electronic equipment grounding, equipment grounding, lightning protection, static protection, system grounding