Grounding Protection (PEC2) - Monterola PDF

GROUNDING PROTECTION GROUNDING PROTECTION A ground is an electrical connection which may either be intentional or accidental between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth. The purpose of grounding a circuit is to fix permanently...

GROUNDING PROTECTION GROUNDING PROTECTION A ground is an electrical connection which may either be intentional or accidental between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth. The purpose of grounding a circuit is to fix permanently a zero voltage point in the system. The grounded line of a circuit should not be broken nor fused to maintain a solid and uninterrupted connection to the ground. Grounding could be accomplished in the following manner. 1. Connection to a buried cold water main. 2.Connection to a rod or group of rods. 3. Connection to a buried ground plate. THE PANELBOARD A panelboard is a single panel or group of panel units designed for assembly in the form of a single panel. This includes buses, automatic overcurrent protective devices, and with or without switches for the control of light, heat or power circuit. It is designed to be placed in a cabinet or cutout box placed in or against a wall or partition and accessible only from the front. Principles applied in installing panel board 1. The approach should be accessible and convenient. 2. The panelboard must be centrally located to shorten the home wiring runs. 3. It must be installed near the load center. As in most cases, panelboard is installed near the kitchen and the laundry where heavy loads are expected. MAIN- is the feeder interior wiring extending from service switch, generator bus, or converter bus to the main distribution. BRANCH CIRCUIT- is defined as the circuit conductors between the final overcurrent device protecting the circuit and the outlets. This means that the branch circuit is only the wiring between the circuit overcurrent protection device such as fuses or circuit breaker and the outlets. However, it is a common knowledge and practice that the branch circuit comprises the entire circuit including the outlet receptacles and other wiring devices. PROTECTION OF THE BRANCH CIRCUIT Any current in excess of the rated current capacity of the equipment or the rated ampacity of the conductor is called overcurrent. The causes of overcurrent are: 1.Overload in the equipment conductors. 2.Short circuit or ground fault As per PEC requirement, conductors shall be protected against overcurrent in accordance with their ampacities (Art. 4.5.1.3) Ampacity is the current- carrying capacity of an electric conductor.  THE CIRCUIT BREAKER AND THE FUSE A circuit breaker is an overcurrent protective device also designed to function as a switch. It is equipped with an automatic tripping device to protect the branch circuit from overload and ground fault. A fuse is also an overcurrent protective device with a circuit opening fusible element which opens when there is an overcurrent in the circuit. It is considered as the simplest and the most common circuit protective device used into the house wiring connection. Advantages of circuit breaker over a fuse 1. The circuit breaker acts as a switch aside from its being an overcurrent device. 2. When there is an overcurrent, the circuit breaker trips automatically and after correcting the fault, it is ready to be switched on again, unlike the fuse which has to be discarded and replaced after it is busted. Advantages of fuse over a circuit breaker 1. One of its major advantage is its reliability and stability. It can stay on its position for years and act when called on to act as designed, unlike the circuit breaker which requires proper maintenance and periodic testing to keep it into a tip-top condition. 2. The cost of a fuse is less than that of a circuit breaker. Standard Ampere Ratings of Fuses and Inverse time circuit breakers 15, 20, 25, 30, 40, 45, 60, 70, 80, 90, 100, 110, 125, 150, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000 and 6000 Fuses, circuit breakers or combinations shall not be connected in parallel. Exception: Circuit breakers or fuses, factory assembled in parallel, and approved as a unit. Position of Knife Switches a) Single-throw Knife Switches. Single-throw knife switches shall be so placed that gravity w not tend to close them. Single-throw knife switches, approved for use in the inverted positio shall be provided with a locking device that will ensure that the blades remain in the ope position when so set. B) Double-throw Knife Switches. Double-throw knife switches shall be permitted to be mounted so that the throw will be either vertical or horizontal. Where the throw is vertical, a locking device shall be provided to hold the blades in the open position when so set. RECEPTACLES AND WIRING DEVICES Receptacles and wiring devices provide essential electrical connections and power distribution in buildings. ELECTRICAL CONDUCTORS AND INSULATORS Electrical Conductors are substances that offer a very low resistance to current flow. Insulators are substances that offer a very high resistance to current flow. LIST OF SOME GOOD ELECTRICAL CONDUCTORS: SILVER, COPPER, ALUMINUM, NICKEL, BRASS, ZINC, PLATINUM, IRON, TIN, AND LEAD. LIST OF SOME INSULATING MATERIALS: RUBBER, PORCELAIN, VARNISH, SLATE, GLASS, MICA, LATEX, ASBESTOS, THERMOPLASTICS, PAPER, OILS, WAX, AND DRY AIR. WIRES AND CABLES Wires are those electrical conductors which are 8 mm2 (AWG no. 8 or smaller, while cables are those larger than the wires. They are either solid or stranded. Stranded wire- consists of a group of wires twisted to form metallic string. The total circular-mil area of a stranded wire is found by multiplying the circular mil area of each strand by the total number of strand. Cord is the term given to an insulated stranded wire. CIRCULAR MIL. This is the unit of cross section in the American wire gauge. The term "mil" means one- thousandth of an inch (0.001 in.). It is the area of a circular wire having a diameter of one mil. To find the number of circular mils in a circle of a given diameter, we have to square the number of mils in the diameter. Area in circular mil = (diameter in mils )2 1 inch = 1,000 mils MCM = 1,000 circular mils SQUARE MIL. It is the area of a square having its side equal to 1 mil. Square mil = (sides)2 = (1 mil)2 = (0.001 in.)2 = 1 x 10-6 in.2 Square mil = 0.7854 x circular mils DIFFERENT TYPES OF CABLES 1. Armored Cable. This type of cable, the type AC is a fabricated assembly of insulated conductors enclosed in flexible metal sheath. Armored cable is used in both exposed and concealed-work. 2. Metal Clad Cable. Cable of the type MC is a factory assembled cable of one or more conductors, each individually insulated and enclosed in a metallic sheath of interlocking tape, or a smooth or corrugated tube. This type is used specifically for services, feeders, branch circuits, either exposed or concealed and for indoor or outdoor work. 3. Mineral Insulated Cable. This type of cable, type MI, is a factory assembly of one or more conductors insulated with a highly compressed refractory mineral insulation and enclosed in liquid-tight and gas-tight continuous copper sheath. The type MI is used in dry, wet or continuously moist location as service, feeders or branch circuit. 4. Nonmetallic Sheathed Cable. Types NM and NMC are factory assembled two or more insulated conductors having a moisture- resistant outer sheath, flame retardant and non-metallic material. These types are used specifically for one or two dwelling not exceeding 3 storey buildings. 5. Shielded Nonmetallic Sheathed Cable. This type of cable, the type SNM, is a factory assembly of two or more insulated conductors in an extruded core or moisture-resistant and flame-retardant material, covered with an overlapping spiral metal tape. This type is used in hazardous locations and in cable trays or in raceways. 6. Service Entrance Cable. This is a single conductor or multiconductor assembly provided with or without an over-all covering, primarily used for services and of the types SE and USE. 7. Underground Feeder and Branch Circuit Cables. This type of cable, the type UF cable is a moisture-resistant cable used for underground, including direct burial in the ground, as feeder or branch circuit. 8. Power and Control Tray Cable. Type TC cable is a factory assembly of two or more insulated conductors with or without associated bare or covered grounding under a metallic sheath. This is used for installation in cable trays, raceways or where supported by a messenger wire. 9. Flat Cable Assemblies. This is an assembly of parallel conductors formed integrally with an insulating material web designed specifically for field installation in metal surface raceway. Cables of this type are the types FC. 10. Flat Conductor Cable. This type of cable, type FCC consists of three or more flat conductors placed edge to edge, separated and enclosed within an insulating assembly. This used for general purpose, appliance branch circuits and for individual branch circuits specifically on hard, smooth, continuous floor surfaces, etc. 11. Medium Voltage Cables. MV cable is a single or multiconductor solid dielectric insulated cable rated 2,001 volts or higher and is used for power systems up to 35,000 volts. The MV cables are of different types and characteristics. RACEWAYS Raceways are channels designed for holding wires, cables or bus-bars, which are either made of metal or insulating materials. The common types of raceways in household wiring are the a) conduits, b) connectors, and c) others. a) Conduits Conduits, pipes or tubings are the most common electrical raceway. According to the type of materials used, conduit maybe classified as either metallic such as steel pipes or nonmetallic such as PVC, and the like. According to its make, conduits maybe classified as: rigid metal, flexible metal, rigid nonmetal and flexible nonmetal. b) Connectors A connector is a metal sleeve usually made of copper that is slipped over and secured to the butted ends of conductors in making joint. A connector is also called a splicing sleeve. c) Other Raceways Aside from the conduits and connectors there are still numerous types and kinds of raceways, among these are the a) conduit couplings, elbows and other fittings; b) conduit supports, such as clamps, hangers, etc; c) cable trays, cablebus; d) metal raceways; e) nonmetal raceways. OUTLETS, RECEPTACLES and other WIRING DEVICES OUTLETS. An outlet is a point in the wiring system at which current is taken to supply utilization equipment. The kinds of outlets are: convenience outlet or attachment cap, lighting outlet, and receptacle outlet. A convenience outlet or attachment cap is a device which by insertion in a receptacle, establishes connection between the conductor of the flexible cord and the conductors connected permanently to the receptacle. A lighting outlet is an outlet intended for direct connection of a lamp holder, a lighting fixture, or a pendant cord terminating in a lamp holder. A receptacle outlet is an outlet where one or more receptacles are installed. TYPES OF WIRES A.TYPES T, TW, THW The most ordinary type of plastic insulated wire is the "type T". It may be used only in dry locations. Some manufactures no longer make the ordinary Type T, instead produce Type TW, which is identical in appearance, but may be used in wet or dry locations. Also available is Type THW, is similar to Type TW but withstand a greater degree of heat, and consequently has a higher ampacity rating in the larger sizes. B.TYPES THΗΝ, ΤΗWN These are comparatively new types of wire, consisting of the basic Type THH and THW but with less thermoplastic insulation, and with a final extruded jacket of nylon. Nylon has exceptional insulating qualities and great mechanical strength, all of which results in a wire which is smaller in diameter than ordinary Types T. TW, TW of corresponding size. С. ТУРЕ ХНHW In appearance, it resembles Types T. TW, THW but because of somewhat thinner layer of insulation, the over- all diameter is smaller. The insulation is "cross-linked synthetic polymer," which has an extraordinary properties as to insulating value, heat resistance, and moisture resistance. It may be used in dry or wet locations. While at present, it is an expensive wire, it would be no surprise if in due course of time, this one single type will replace all the many types and subtypes of Type T or R now recognized by the Code. D. RUBBER-COVERED WIRE It consists of copper conductor, tinned to make it easier to remove the insulation, and for easy soldering. Over the copper is a layer of rubber, the thickness of which depends on the size of the wire. Then follows an outer fabric braid which is saturated with moisture- and-fire-resistant compounds; if it is set on fire with a blowtorch, the flame dies out when the torch is removed. E. OTHER TYPES Other types such as the basic Type R, which is suitable for only in dry locations, is no longer being made. The most ordinary kind is Type RHW, which may be used for dry or wet locations. Types RH and RHH have insulation which withstands more heat and therefore have a higher ampacity in the larger size. They may be used only in dry locations. KINDS OF LOCATIONS DAMP LOCATION Partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subjected to moderate degree of moisture, such as some basements, some barns, and some cold-storage warehouses. DRY LOCATION A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction. WET LOCATION Installations underground or in concrete slabs or masonry in direct contact with the earth, and location subject to saturation with water or other liquids, such as vehicle washing areas, and locations exposed to weather and unprotected. HAZARDOUS (CLASSIFIED) LOCATIONS Locations where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. 1. Class I Locations. Class I locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures. a) Class I, Division 1. A Class I, Division 1 location is a location: I) in which ignitable concentrations of flammable gases or vapors can exist under normal operating conditions; or ii) in which ignitable concentrations of such gas vapors may exist frequently because of repair or maintenance operations or because of leakage; or iii) in which breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment. b)Class I, Division 2. A Class I, Division 2 location is a location: i) in which volatile flammable liquids or flammable gases are handled, processes, or used, but in which the liquids, vapors, or gases will normally be confines within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers ог systems, or in case of abnormal operation of equipment; or ii) in Class 1, Division 2 which ignitable concentrations of gases or vapors are normally or nonhazardous prevented by positive mechanical ventilation, and which might location become hazardous through failure or abnormal operation of the ventilating equipment; iii) that is adjacent to Class I, Division 1 location, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive ventilation from a source of clean air, and effective safeguards against ventilation failure are provided. 3. Class III Locations. Class III locations are those that are hazardous because of the presence of easily combustible fibers of flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures. a) Class III, Division 1. A Class III, Divisions 1 location is a location in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used. b) Class III, Division 2. A Class III, Division 2 location is a location in which easily ignitible fibers are stored or handled.