Module 1: Building Electrical Systems PDF

Module 1: Building Electrical Systems Topic 3: Electrical Systems in Buildings An electrical system, within the context of a building, is a network of conductors and equipment designed to carry, distribute, and convert electrical power safely from the point of delivery or generation to the various...

Module 1: Building Electrical Systems Topic 3: Electrical Systems in Buildings An electrical system, within the context of a building, is a network of conductors and equipment designed to carry, distribute, and convert electrical power safely from the point of delivery or generation to the various loads around the building that consume the electrical energy. Basics of Electricity Distribution  Earthing (or grounding) systems and bonding  Electric wiring  Industrial installations  Lighting controls  Light sources, Lamps, Lighting design  Telecommunication installations The basics of electrical installations are:  Lighting – providing illumination both inside and outside of the buildings.  Exhaust fans – providing ventilation both inside and outside of the buildings.  Use of portable and non-portable electrical machines or appliances and their wiring network, including sub-main wiring, cable, overhead lines, etc. including control panels and switches. Transmission and Distribution Transmission lines, transformers, substations, and other equipment have voltages 100 kV (or 100,000 Volts) and above. Types of Electric Power Distribution Systems According to the nature of the supply  AC Distribution System  Primary Distribution System  Secondary Distribution System  DC Distribution System According to a type of construction  Overhead system  Underground system TYPES OF ELECTRICAL SERVICE IN THE PHILIPPINES. There are two main types of residential electrical service in the Philippines. MANILA AND CITIES: Three-wire 120/240V Systems. In Manila, Iloilo City, and other large Philippine cities, residences are supplied with 240-volt, alternating current, 60- cycle power using two wire service drop to the residence. Power from the utility transformer to the residence arrives through three wires, two 120 V AC load (“hot”) wires and a single neutral. Circuits in residence are generally wired to supply 240 V AC to outlets using the two 120 VAC load wires, much the same as a heavy appliance (dryer, hot water heater etc.) would be supplied in the U.S. All small and large appliances sold in the Philippines are designed to use 240 V AC, 60 cycle (Hz). However, it is possible to wire in 120 VAC circuits and outlets by using only one of the load wires and a neutral one. These 120 V outlets are seen in hotels, some condos and other places that expect American visitors. Visitors must keep in mind that the Philippines uses the same style of wall outlets as you see in America, but that the outlet is supplying 240 V, not 120 V. Plugging a 120 V appliance into a 240 V outlet will generally destroy the appliance. OUTSIDE OF BIG CITIES: Two-wire 240V Systems Areas outside of the old established cities were electrified later and used a different and more economical system using a two-wire service drop to the residence. This consists of one 240 VAC load wire and one neutral wire. 120 VAC cannot be supplied by this type of system unless the property owner, at his own expense and with the cooperation of the utility company, installs his own transformer at the utility pole, a transformer having a secondary winding which can supply 120 VAC. Single-Phase Power Supply In a Single-Phase Power Supply, the power is distributed using only two wires called Phase and neutral. Since AC Power takes the shape of a sinusoidal wave, the voltage in a single-phase supply peaks at 900 during the positive cycle and again at 2700 during the negative cycle. Single-phase connections are designed for household supplies and residential homes. This is because most appliances, such as televisions, lights, fans, refrigerators, and so on, require only a small amount of electricity to function. Usually, the single-phase voltage is 230V and the frequency is 60Hz in the Philippines. Three-Phase Power Supply A Three-Phase Power Supply consists of three power wires (or the three phases). Additionally, depending on the type of the circuit (which there are two types: Star and Delta), and can be with 4th wire as neutral wire. In a three-phase power supply system, each AC Power Signal is 1200 out of phase with each other. Three-phase electric power (3-phase), is a type of alternating current that is commonly used in power generation, transmission, and distribution. Thick wires on tall transmission towers carry high-voltage electricity from power plants to local communities. It is a type of polyphase system that uses three wires (or four if a neutral return wire is used) and is the most common method used by electrical grids around the world to transfer power. As a result, three-phase power is preferable for high-tension power loads and it can carry up to 415V. Thinner wires on smaller towers or electric poles carry much lower voltage power to homes, businesses and other load centers. Distribution Voltages  Primary: 4.16kV, 13.8kV, 34.5kV, 69kV  Secondary: 110/115V, 220/230V Home Electrical Systems A home’s electrical system includes incoming power lines, an electric meter, a service panel, subpanels, household wiring, electrical boxes, receptacles (outlets), switches, and, of course, the appliances, lights, and equipment that put the power to work. Other electrical systems in a house include wiring for home entertainment, such as cable television, home theaters, and audio systems, not to mention wiring for home communications such as telephones, security systems, doorbells, and intercoms. Protection Devices in Electrical Installations Protection devices or protective devices for electrical circuits accomplish two main functions namely consistency as well as protection. Protection is assured through detaching power supply in a circuit through overcurrent protection, which removes fire hazards and electrocution. Designers must take time to know the different protection devices for circuits. Protection devices used to protect circuits from extreme voltages or currents. What is a Protective Device? A device used to protect equipment, machinery, components and devices, in electrical and electronic circuit, against short circuit, over current and earth fault, is called as protective devices. Types of Protective Devices 1. Fuse Wire or Fuse 2. MCB – Miniature circuit breaker 3. ELCB – Earth Leakage Circuit Breaker 4. ELCB & MCB 5. Earthing or Grounding 6. Ground-Fault Circuit Interrupter (GFCI) Fuse Wire or Fuse A fuse is a device that protects electrical systems against potentially dangerous power surges and excessive temperatures. When subjected to extreme conditions, the fuse will blow or burn out. Unlike a circuit breaker, a fuse cannot be reset. It must be replaced. Cartridge Fuses Blade Fuse Fuse Boxes A fuse box is a metal box that contains screw-in fuses and cartridge fuses. Cartridge fuses normally manufactured in the range of 2A. to 100A. Fuse box is smaller than the electrical service panels found in most old homes today. Miniature Circuit Breaker (MCB) A circuit breaker is one kind of electrical switch used to guard an electrical circuit against short circuit otherwise an overload which will cause by excess current supply. The basic function of a circuit breaker is to stop the flow of current once a fault has occurred. Not like a fuse, a circuit breaker can be operated either automatically or manually to restart regular operation. Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A. Residential Commercial and Industrial 1P - Single pole switch of circuit breaker: Only one connecting plug, it can only break one phase line, this switch is only suitable for controlling one-phase live wire. 2P - Two pole switch of circuit breaker: Two connecting plugs, one is connected to the phase line and the other is connected to the zero line. 3P - Three pole switch of circuit breaker: Three connecting plugs, which are connected to the live wires. This switch is suitable for controlling three-phase 380V circuit. 4P - Four pole switch of circuit breaker: Four connecting plugs, three are connected to the live wires and the remaining is connected to the zero line. This switch is suitable for controlling three-phase four-wire system circuit. 1P+N - Single pole switch with zero terminal (the zero line doesn’t break) 3P+N - Three pole switches with zero terminal (the zero line doesn’t break) Molded Case Circuit Breaker (MCCB) or Power Circuit Breaker (PCB) It is another type of electrical protection device that is used when the load current exceeds the limit of a miniature circuit breaker. The MCCB protects against overload, and short circuit faults and is also used for switching the circuits. It can be used for higher current rating and fault levels in domestic applications. The wide current ratings and high breaking capacity in MCCB find their use in industrial applications. MCCB can be used for protection of capacitor banks, generator protection, and main electric feeder distribution. It offers adequate protection whenever an application requires discrimination, adjustable overload setting, or earth fault protection. MCCB is available from 100 A and higher up to 100 kA. Residual Current Device (RCD) The RCD-residual current device (or) RCCB-residual current circuit breaker is a safety device that notices a problem in your home power supply and then turns OFF in 10-15 milliseconds to stop electric shock. A residual current device does not give safety against short circuits or overload in the circuit, so we cannot change a fuse instead of an RCD. RCD have become mandatory components installed in every household switchboard and in every new installation. They are often confused with overcurrent circuit breakers, but their operation and functions are completely different. Professionals distinguish three types of RCDs based on the differential current they can handle. These are, respectively:  High-sensitivity residual current devices (up to 30 mA), which are used in kitchens, bathrooms, workshops, studios, etc. – where the risk of fire caused by a faulty installation or appliance is quite high;  Medium-sensitivity residual current devices (from 30 to 500 mA), which are ideal for protecting general-purpose circuits in residential buildings or on construction sites;  Low-sensitivity residual current devices (from 500 mA up), which are used for circuits with high leak current and as main circuit breakers for the entire home electrical installation. Earth Leakage Circuit Breaker (ELCB) An ELCB is one kind of safety device used for installing an electrical device with high earth impedance to avoid shock. These devices identify small stray voltages of the electrical device on the metal enclosures and intrude the circuit if a dangerous voltage is identified. The main purpose of the Earth leakage circuit breaker (ELCB) is to stop damage to humans & animals due to electric shock. Ground Fault Circuit Interrupter (GFCI) A ground fault circuit interrupter (GFCI) can help prevent electrocution. If a person’s body starts to receive a shock, the GFCI senses this and cuts off the power before he/she can get injured. GFCIs are generally installed where electrical circuits may accidentally come into contact with water. They are most often found in kitchens, bath and laundry rooms, or even out-of-doors or in the garage where electric power tools might be used. Earthing or Grounding Working on home electrical systems can be justifiably intimidating. Home wiring can be dangerous, depending upon the type. Standard-voltage electrical wiring, which serves electrical outlets, lights, and appliances must be handled carefully to avoid shock or electrocution. But, if you follow expert instructions and turn off the power to circuits and devices before working on them, you can do this type of work safely. One of the keys to safely working on an electrical system is to ensure that all circuits are properly grounded. Electrical current travels in a continuous closed path from the source (your home’s electrical panel) through a device that uses the power, such as a light, and then back to the source. But if the electricity doesn’t have to flow through wires for the return trip to the source. It can return to the source through any conductor—including a person. The conductor just has to contact the earth directly or touch a conductive material (such a water or metal) that goes to the earth. If you accidentally become the conducting link in an electrically live circuit, you’ll get a shock—or worse. Grounding is an integral part of any properly operating electrical system. In residence, grounding protects the occupants by providing a safe pathway for unwanted electricity that might otherwise create a hazard. Electricity always takes the easiest flow path to earth. A ground is a low-resistance conducting connection between electrical circuits, equipment, and the earth. Grounding is used to provide a safe path for a fault current to flow. A complete ground path must be maintained when installing switches, light fixtures, appliances, and receptacles. In a properly grounded system, the unwanted current flow blows fuses or trips circuit breakers. Once a fuse is blown or a circuit breaker is tripped, the circuit is open, and no additional current will flow. The grounding system is a basic part of any electrical installation, and aims to: - Limit the potential difference between metallic masses and ground. - Make sure the protection devices operate. - Eliminate or reduce the risk posed by a fault in the electrical equipment used. System and Equipment Grounding Safety Grounding is usually done at two levels: system grounding and equipment grounding. The system ground is a special circuit designed to protect the entire distribution system of a residence. Equipment ground is essentially a circuit designed to protect individual components of an electrical system. Grounded conductors are used to providing a path to the ground for system and equipment grounds. A grounded conductor is one that has been grounded on purpose. Grounded conductors are typically identified with green or green and yellow markings and may be installed as bare conductors. The two most popular methods used for grounding an electrical system are electrode grounding and water pipe grounding. Other grounding methods use a concrete- encased electrode or a ground ring, both of which are less common in residential wiring systems. Electrode Grounding An electrode is a long metal rod used for grounding that makes contact with the earth. When no satisfactory grounding electrode is readily available, the common practice is to drive one or more metal rods (connected in parallel) into the ground. The electrode and circuit must provide a flow path to the earth with less than 25Ω of resistance. Water Pipe Grounding A water pipe ground uses the underground metal pipe that supplies a residence with water and is typically the best electrical ground for a residential electrical system. Water pipes work well as grounds because the large surface area of the pipe is in contact with the earth, as it connects the municipal water main to the water distribution system in residence. This large surface area reduces resistance and allows any unwanted electricity to easily pass through the pipe to the earth. When a water pipe is used for grounding, the water pipe run must never be interrupted by a plastic fitting or have an open section of plumbing. Equipment Grounding Equipment grounding's main purpose is to protect individual electrical devices. Equipment grounding safely grounds any devices or appliances attached to an electrical system or plugged into receptacles inside a home. For example, when a refrigerator has not been properly grounded, the electrical current caused by a short will seek the easiest path to earth. Unfortunately, the human body is an electrical conductor and allows current to reach the earth by traveling through the body (electric shock). Proper equipment grounding protects the body by harmlessly conducting unwanted electricity to the ground. Grounding Small Appliances Small appliances are easily incorporated into a grounded system. Most small electrical appliances are designed with three-prong grounded plugs that match a standard three- prong grounded receptacle. The U-shaped blade of the plug and the U-shaped hole in the receptacle are the ground connections. The U-shaped blade of a plug is longer than the current-carrying blades. The added length ensures a strong ground connection while the plug is being inserted or removed from a receptacle. The ground wire is connected to all receptacles and metal boxes to provide a continuous pathway for short-circuit current. The ground wire may be connected to each box using a pigtail, screw, or ground clip.  Three-Prong Grounded Receptacle and Three-Prong Grounded Plug Grounding Wire Grounding wires are primarily in place to protect the outlet and surrounding area in case of an overload or power surge. If a transient charge (the technical term for an overload) happens to pass through that outlet, the grounding wire is there to redirect the charge into itself, or “to ground.” The outlet is able to send the electricity harmlessly away without it presenting any safety hazard or damaging other wires. Alternate Source of Electricity Diesel Generator is the most widely used alternative source of power in facilities today. Its ability to provide continuous power as long as it has a supply of fuel makes it well- suited for providing both long- and short-term backup power. It is useful that supply electrical power during a power outage and prevent discontinuity of daily activities or disruption of business operations. Having an emergency generator will allow you to keep the necessary appliances running in your home, commercial and industrial operations. Most generator-based systems are designed to automatically provide power to designated loads in the event of an interruption in service. When power is lost, the generator automatically starts. Once the generator comes up to speed, a switch automatically transfers the load from utility power to the output of the generator. Depending on the size of the generator, this transfer typically takes place in 30 seconds or less. Once utility company power is restored, the load is transferred back and the generator shuts down. While generator systems are very reliable, they are not maintenance-free. If the systems are to perform as needed, when needed, they must have regularly scheduled maintenance. Portable Standby Generator Standby (Backup) Commercial and Industrial Generator (Outdoor) Standby (Backup) Commercial and Industrial Generator (Indoor)