Lecture 3.pdf ,
- 1. UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR ELECTRONICS ENGINEERING DEPARTMENT ELE-410 INDUSTRIAL ELECTRONICS LECTURE # 03 BY DR. ADAM KHAN 1
- 2. • Text Book: Electric Motors and Control Systems • By Frank D Petruzella 2nd Edition Chapter 1: Safety in the Workplace 2
- 3. Grounding—Lockout—Codes • Grounding and Bonding • “Grounding” is the intentional connection of a current carrying conductor to the earth. • Unintentional or accidental grounding is considered a fault in electrical wiring systems or circuits. • For AC premises wiring systems in buildings and similar structures, this ground connection is made on the premise side of the service equipment and the supply source, such as a utility transformer 3
- 4. Grounding and Bonding (Contd…) • The prime reasons for grounding are: • To limit the voltage surges caused by lightning, utility system operations, or accidental contact with higher-voltage lines. • To provide a ground reference that stabilizes the voltage under normal operating conditions. • To facilitate the operation of overcurrent devices such as circuit breakers, fuses, and relays under ground-fault conditions. • “Bonding” is the permanent joining together of metal parts that aren’t intended to carry current during normal operation (an electrical conductive path that can safely carry current under ground- fault conditions) 4
- 5. Grounding and Bonding (Contd…) • The prime reasons for bonding are: • To establish an effective path for fault current that facilitates the operation of overcurrent protective devices. • To minimize shock hazard to people by providing a low-impedance path to ground. Bonding limits the touch voltage when non-current-carrying metal parts are unintentionally energized by a ground fault. • The Code requires all metal used in the construction of a wiring system to be bonded to, or connected to, the ground system. 5
- 6. Grounding and Bonding (Contd…) • Figure 1-9 illustrates the ground- fault current path required to ensure that overcurrent devices operate to open the circuit. • The main bonding jumper is used to provide the connection between the grounded service conductor and the equipment grounding conductor at the service. 6
- 7. Grounding and Bonding (Contd…) • A grounding system has two distinct parts: • System grounding is the electrical connection of one of the current carrying conductors of the electrical system to the ground. • Equipment grounding is the electrical connection of all the metal parts that do not carry current to ground. • Conductors that form parts of the grounding system include the following: • Grounded conductor is a conductor that has been intentionally grounded. • Grounding electrode conductor is a conductor used to connect the equipment grounding conductor or the grounded conductor 7
- 8. Grounding and Bonding (Contd…) • Equipment grounding conductor (EGC) is an electrical conductor that provides a low-impedance ground path between electrical equipment and enclosures within the distribution system. • Effectively grounding the motor frame forces it to take the same zero potential as the earth, thus preventing injuries and damages. 8
- 9. GFCI • A ground fault is defined as an unintentional, electrically conducting connection between an ungrounded conductor of an electric circuit and the normally noncurrent-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth. • The ground-fault circuit interrupter (GFCI) is a device that can sense small ground-fault currents. • The GFCI is fast acting; the unit will shut off the current or interrupt the circuit within 1/40 second after its sensor detects a leakage as small as 5 milliamperes (mA). • Most circuits are protected against overcurrent by 15 ampere or larger fuses or circuit breakers. 9
- 10. GFCI (Contd…) • The device compares the amount of current in the ungrounded (hot) conductor with the amount of current in the grounded (neutral) conductor. • Under normal operating conditions, the two will be equal in value. • If the current in the neutral conductor becomes less than the current in the hot conductor, a ground-fault condition exists. • The amount of current that is missing is returned to the source by the ground-fault path. • Whenever the ground-fault current exceeds approximately 5 mA, the device automatically opens the circuit to the receptacle. 10
- 11. Lockout and Tagout • Electrical “lockout” is the process of removing the source of electrical power and installing a lock, which prevents the power from being turned ON. • Electrical “tagout” is the process of placing a danger tag on the source of electrical power, which indicates that the equipment may not be operated until the danger tag is removed. • Electrical lockout and tagout is used when servicing electrical equipment 11
- 12. Lockout and Tagout (Contd..) • The following are the basic steps in a lockout procedure: • Prepare for machinery shutdown: Document all lockout procedures in a plant safety manual. This manual should be available to all employees and outside contractors working on the premises. • Machinery or equipment shutdown: Stop all running equipment by using the controls at or near the machine. • Machinery or equipment isolation: Disconnect the switch (do not operate if the switch is still under load). • Lockout and tagout application: Lock the disconnect switch in the OFF position. Some switch boxes contain fuses, and these should be removed as part of the lockout process. • Tag the lock with the signature of the individual performing the repair and the date and time of the repair. 12
- 13. Lockout and Tagout (Contd..) • basic steps in a lockout procedure: • Release of stored energy: All sources of energy that have the potential to unexpectedly start up, energize, or release must be identified and locked, blocked, or released. • Capacitors retain their charge for a considerable period of time after having been disconnected from the power source. • Verification of isolation: Use a voltage test to determine that voltage is present at the line side of the switch or breaker. • Ensure that your voltmeter is working properly by performing the “live-dead-live” check before each use: • Lockout/tagout removal: Remove tags and locks when the work is completed. Each individual must remove his or her own lock and tag. 13
- 14. Electrical Codes and Standards • OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION (OSHA) • In 1970, Congress created a regulatory agency known as the Occupational Safety and Health Administration (OSHA). • The purpose of OSHA is to assure safe and healthful working conditions for working men and women by authorizing enforcement of standards developed under the Act. • OSHA’s electrical standards are designed to protect employees exposed to dangers such as electric shock, electrocution, fires, and explosions. 14
- 15. Electrical Codes and Standards (Contd..) • NATIONAL ELECTRICAL CODE (NEC) • The National Electrical Code (NEC) comprises a set of rules that, when properly applied, are intended to provide a safe installation of electrical wiring and equipment. • The NEC is the most widely adopted code in the world. • An “Article” of the Code covers a specific subject. For example, Article 430 of the NEC covers motors and all associated branch circuits, overcurrent protection, overload, and so on. • The installation of motor-control centers is covered in Article 409, and air-conditioning equipment is covered in Article 440. 15
- 16. Electrical Codes and Standards (Contd..) • Article 430 on motors is the longest article in the Code. • One of the reasons for this is that the characteristics of a motor load are quite different from heating or incandescent lighting loads and so the method of protecting branch circuit conductors against excessive current is slightly different. • Non-motor branch circuits are protected against overload conditions. • Whereas motor branch circuits are protected against overload conditions as well as ground faults and short circuits. 16
- 17. Electrical Codes and Standards (Contd..) • The use of electrical equipment in hazardous locations increases the risk of fire or explosion. • Hazardous locations can contain gas, dust (e.g., grain, metal, wood, or coal), or flying fibers (textiles or wood products). • Articles 500 through 504 and 510 through 517 provide classification and installation standards for the use of electrical equipment in these locations. • Explosion-proof apparatus, dust ignition- proof equipment, and purged and pressurized equipment are examples of protection techniques that can be used in certain hazardous ( classified) locations. 17
- 18. Electrical Codes and Standards (Contd..) • NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) • The National Fire Protection Association (NFPA) develops codes governing construction practices in the building and electrical trades. • It is the world’s largest and most influential fire safety organization. • NFPA has published almost 300 codes and standards, including the National Electrical Code, with the mission of preventing the loss of life and property. 18
- 19. NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) (Contd..) • Fire prevention is a very important part of any safety program. • It is important to know where your fire extinguishers are located and how to use them. • Icons found on the fire extinguisher indicate the types of fire the unit is intended to be used on. 19
- 20. NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) (Contd..) • In case of an electrical fire, the following procedures should be followed: • Trigger the nearest fire alarm to alert all personnel in the workplace as well as the fire department. • If possible, disconnect the electric power source. • Use a carbon dioxide or dry-powder fire extinguisher to put out the fire. Under no circumstances use water, as the stream of water may conduct electricity through your body and give you a severe shock. • Ensure that all persons leave the danger area in an orderly fashion. • Do not re enter the premises unless advised to do so. 20
- 21. NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) (Contd..) • There are four classes of fires, categorized according to the kind of material that is burning: • Class A fires are those fueled by materials that, when they burn, leave a residue in the form of ash, such as paper, wood, cloth, rubber, and certain plastics. • Class B fires involve flammable liquids and gases, such as gasoline, paint thinner, kitchen grease, propane, and acetylene. • Class C fires involve energized electrical wiring or equipment such as motors and panel boxes. • Class D fires involve combustible metals such as magnesium, titanium, zirconium, sodium, and potassium. 21
- 22. Electrical Codes and Standards (Contd..) • NATIONALLY RECOGNIZED TESTING LABORATORY (NRTL) • Article 100 of the NEC defines the terms “labeled” and “listed,” which are both related with product evaluation. • Labeled or listed indicates the piece of electrical equipment or material has been tested and evaluated. • In accordance with OSHA Safety Standards, a Nationally Recognized Testing Laboratory (NRTL) must test electrical products for conformity to national codes and standards before they can be listed or labeled • Pakistan National Accreditation Council, Ministry of Science and Technology, Government of Pakistan • http://pnac.gov.pk/TestingCalibrationLaboratoies 22
- 23. Pakistan National Accreditation Council • Pakistan National Accreditation accredited first laboratory in 2004. Since then, the PNAC Laboratory Accreditation Scheme accredits laboratories that conduct tests in the following field of Testing: • Microbiological • Chemical • Food • Construction and Construction Products • Electrical • Environmental • Textiles • Petrochemicals • Pharmaceuticals 23 http://pnac.gov.pk/TCLA
- 24. Pakistan National Accreditation Council • PNAC accreditation covers a broad range of calibration activities. Calibration laboratories support the activities of other accredited testing laboratories, as well as provide accurate measurement and traceability to the manufacturing sector, engineering sector, construction sector, and equipment makers. • Temperature • Pressure, Vacuum and Flow • Optical • Electrical Calibration • Radiological Calibration • Magnetics • Acoustics 24 http://pnac.gov.pk/TCLA
- 25. Electrical Codes and Standards (Contd..) • NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION (NEMA) • The National Electrical Manufacturers Association NEMA) is a group that defines and recommends safety standards for electrical equipment. • Standards established by NEMA assist users in proper selection of industrial control equipment. • As an example, NEMA standards provide practical information concerning the rating, testing, performance, and manufacture of motor control devices such as enclosures, contactors, and starters. 25
- 26. Electrical Codes and Standards (Contd..) • INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC) • The International Electrotechnical Commission (IEC) is a Europe-based organization made up of national committees from more than 60 countries. • There are basically two major mechanical and electrical standards for motors: • NEMA in North America and IEC in most of the rest of the world. • NEMA standards tend to be more conservative—allowing more room for “design interpretation while IEC standards tend to be more specific designed with less over current tolerance. • As an example, a NEMA-rated motor starter will typically be larger than its IEC counterpart. 26
- 27. Electrical Codes and Standards (Contd..) • INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS (IEEE) • The Institute of Electrical and Electronics Engineers (IEEE) is a technical professional association whose primary goal is to foster and establish technical developments and advancements in electrical and electronic standards. • Through its technical publishing, conferences, and consensus-based standards activities, the IEEE produces more than 30 percent of the world’s published literature in electrical and electronic engineering. 27