Building Electrical Service Equipment PDF

Building Electrical Service Equipment  Building Electrical Service Equipment It provides illumination or lighting, and any other facilities required for the building or structure to be occupied for its intended purpose. Building Electrical Service Equipment  Building Electrical...

Building Electrical Service Equipment  Building Electrical Service Equipment It provides illumination or lighting, and any other facilities required for the building or structure to be occupied for its intended purpose. Building Electrical Service Equipment  Building Electrical Service Equipment Service Entrance Conductors Service Entrance Switchboards Panelboard Building Transformer Service Entrance Conductor  Service Drop Overhead wires extended from a pole-mounted distribution transformer to the building’s service entrance. Service Lateral Underground (buried) service entrance conductors. Service entrance conductors must be insulated (covered with nonconducting material) except the neutral, which may be bare in overhead installations. The service entrance neutral can be bare copper in a conduit (a tube or trough for protecting electrical wiring) or cable. Copper cable is a group of two or more copper wires bundled together in a single sheath or jacket. Electrical Conduit Copper Wire Service Entrance Service Entrance Equipment Receive the service entrance conductors. The service equipment includes a method of measuring power (metering equipment), a method of cutting off power (main disconnect or switch gear), and overcurrent protection devices (circuit breakers or fuses) that protect the service entrance conductors.  ELECTRIC METER An instrument that is used by the utility company to measure and record electrical energy consumed. Examples of Electric Meter Feed-through meter Used in building services rated up to 400 A. A small electric motor with a speed that is proportional to the power consumed. C/T (Current-transformer) Used for services rated above 400 A. Housed in an enclosure called a C/T cabinet that is part of the service entrance equipment.  Service Disconnect A required part of the service entrance equipment that allows electrical service from the utility company to be switched off so that power is disconnected to the building installation. A set of fuses or a circuit breaker that protects the service entrance conductors. Switchboard A switchboard is a key component in an electrical distribution system used in commercial and industrial facilities. It divides electrical power into branch circuits and provides protection for each circuit with circuit breakers or fuses. Switchboards can disconnect circuits manually or automatically and are typically floor-mounted with high current capacities (1200-6000 amperes) and operate at voltages below 600 volts. They are accessed from both the front and rear of the cabinet. Switchboard Panelboards One or more metal cabinets or cutout enclosure placed in or against a wall or partition that is accessible from the front that serve as a single unit, including buses, automatic overcurrent protection devices (fuses or circuit breakers). It is equipped with or without switches for the control of light, heat, and power circuits. A typical panelboard consists of a sheet metal box, called a cabinet, and a cover that encloses and conceals the panelboard interior to limit access to power distribution components. Building Transformers A transformer is a static device. The word ‘transformer’ comes from the word ‘transform’. Transformers are used in transmitting and distributing power from the power plant to a substation. Building transformers are rated in kilo-volt-amperes (kVA).  Every transformer comes with a nameplate that typically identifies: Primary and Required Rated kVA Impedance secondary voltage clearances  Step-up Transformers Step-down Transformers A transformer in which voltage across A transformer in which voltage across secondary is greater than primary voltage. secondary is lesser than primary voltage. The number of turns in the secondary coil is The number of turns in the secondary coil is greater than in the primary coil. less than in the primary coil. It delivers higher voltage than the source. It delivers lower voltage than the source. Step-up Transformers Step-down Transformers Classification of Transformers As per the cooling system VENTILATED DRY-TYPE TRANSFORMER LIQUID-IMMERSION TRANSFORMER HAS ITS CORE AND COILS IN A GASEOUS OR DRY COMPOUND. HAS ITS CORE AND COILS IMMERSED IN AN DRY-TYPE DISTRIBUTION TRANSFORMERS INSULTATING LIQUID. ARE USUALLY FOUND INSIDE LARGER COMMERCIAL/INDUSTRIAL FACILITIES AND ARE GENERALLY OWNED BY THE FACILITY.  Liquid-immersion transformer Ventilated dry-type transformer As per phase Single-Phase Transformer A type of transformer which consists of only one pair of the transformer coils or windings, i.e., one primary winding and one secondary winding, and is used for transforming the single-phase alternating voltage to the desired value. Three-Phase Transformer A transformer consists of three pairs of transformer windings placed in a three-section iron core, where each section contains a pair of a primary winding and a secondary winding and is used to step-up or step down the three-phase alternating voltage. Types of Three-Phase Transformer  Types of Three-Phase Transformer Delta-connected Wye-connected Delta-wye (Δ-Y) Transformer Transformer Transformer The delta (Δ) connection in transformers involves connecting The star (Y) connection in An electrical device that converts the windings in a series to form a transformers involves three three-phase power without a triangle, with each winding independent windings neutral wire into three-phase power connected head to toe. connected at a common point, with a neutral wire. There is no common point for all the neutral or star point. Various transformer configurations phases. This configuration provides This configuration forms a Y- are available, including wye-wye (Y- only a single voltage level, shape, with the center point Y), delta-delta (Δ-Δ), and wye-delta specifically the phase-to-phase acting as the common return (Y-Δ), allowing flexibility in power voltage. for the neutral conductor. distribution and voltage To obtain other voltage levels, step- transformation. up or step-down transformers are required. Delta-connected Transformer Wye-connected Transformer (Y) Delta-wye (Δ-Y) Transformer  As per core Core Type Shell Type Transformer Transformer In a core-type transformer, the Consists of one central limb and two magnetic circuit consists of two outer limbs. Both primary and vertical sections called limbs and two secondary windings are placed on the horizontal sections called yokes. The central limb. The function of the two primary and secondary windings are outer limbs is to complete the path of divided and placed on each limb to low reluctance for magnetic flux. minimize leakage flux. The major advantage of the shell type One key advantage of this design is transformer is that it gives better that it allows for easier dismantling, support against the electromagnetic making repair and maintenance more forces between the current carrying convenient. conductors.  Overcurrent Protection: Fuses and Circuit Breakers  Overcurrent Protection (OCP) Device A protective device, such as a circuit breaker or fuse, safeguards the building's electrical service or individual circuits from excessive current flows. It prevents circuit components from overheating by interrupting the current when it reaches a level that could cause dangerous temperature increases in conductors, thereby reducing the risk of fire or damage. Fuses and Circuit Breaker Automatic overcurrent protection devices, such as circuit breakers, are designed to open a circuit if the current flowing through it exceeds its rated capacity in amps. This action prevents damage and potential hazards by interrupting the current flow when it exceeds the device's rating. Types of Overcurrent Protection Devices Circuit Breakers An overcurrent protection device, such as a circuit breaker, serves two main purposes: 1. Manual Switching: It can be manually opened and closed to control the circuit. 2. Automatic Protection: It automatically "trips off" to open the circuit when the current exceeds its rating, instantly interrupting current flow. After tripping, it can be reset, allowing electricity to flow again if the current remains within the circuit's rating. These devices are classified by their voltage rating (maximum voltage they can handle) and current- carrying capacity (amperage). The voltage rating should not be exceeded by the electrical circuit being protected. They protect the ungrounded (hot) conductors and come in different types: - Single Pole (SP): Protects a single ungrounded conductor. - Two Pole (2P): Protects two ungrounded conductors, typically used in 240 V circuits. - Three Pole (3P): Protects three ungrounded conductors, used in three-phase circuits. Thermal-magnetic Type The most popular type of circuit breaker is the thermal circuit breaker. It features a bimetallic strip that bends when heated by the power loss caused by excessive current flow. As the current increases, the strip heats up and bends, eventually triggering a release mechanism that opens the contacts and interrupts the circuit. This design allows the circuit breaker to handle brief overloads, such as those encountered during motor startup, without tripping immediately. The delay in tripping is due to the time required for the heat to cause significant damage, providing a buffer against nuisance tripping while still ensuring safety. Fuses An overcurrent protection device that consists of a strip of metal with a low melting temperature. Under normal operation, electricity flows through the metal strip. However, when its current rating is exceeded, the metal strip heats up and melts and the circuit is opened, thereby interrupting current flow. In this case, it is said that the fuse has “blown.” A new fuse of the same rating must replace a blown fuse, which is discarded. Three Basic Types of Fuses  Plug Fuses Screw into sockets much like a lamp. They are rated from 5 A to 30 A.  Edison-base Plug Fuse Has threads similar to an ordinary incandescent lamp base. Interchangeable regardless of rating, allowing a 30 A fuse to improperly protect a 20 A circuit. This interchangeability makes Edison fuses unsafe, so they are no longer allowed in new and retrofit installations.  Type S Plug Fuses Have bases of different sizes that match the fuse rating to the circuit rating. Allowed in new and retrofit installations.  Cartridge Fuses Cylindrical in shape and available in two types: ferrule-contact type and knife-blade type. Allowed in new and retrofit installations.  Ferrule-contact Type Have round copper contacts at their end and are rated up to 60 A.  Knife-blade Type Has flat blades sticking out at each end.  Time Delay Fuses Can handle an overload for a fraction of a second without blowing. Desirable on circuits serving electric motors such as air conditioners and machinery because motors draw much more current at startup than during normal operation. Circuit breakers are often preferred over fuses because they can be easily reset after tripping, whereas fuses need to be replaced. However, circuit breakers can deteriorate over time and may lose sensitivity with each trip. To maintain optimal overcurrent protection, they should be periodically replaced. Overcurrent protection devices are typically installed in enclosures like switchboards, panelboards, motor control centers, or individual enclosures to ensure safety and proper operation of electrical systems. Adequate overcurrent protection is the single-most important safety feature in any electrical circuit as it safeguards conductors and equipment. Although an OCP device safeguards against overheating and fire, it does not protect an occupant from electrical shock.  OCP Device Ratings Have two current ratings: overcurrent and amperes interrupting current.  Overcurrent Rating The highest amperage that an overcurrent protection (OCP) device can carry continuously without overheating is known as its rated continuous current. If the current flowing through the device exceeds this rating for a significant period, the OCP device will open (trip) to protect the circuit from damage caused by excessive current.  Interrupting Rating Overcurrent protection (OCP) devices must have an interrupting rating that is adequate for the maximum possible fault current (short-circuit current) they might encounter. If an OCP device is not rated to interrupt at the available fault current, it risks exploding while trying to clear the fault. This can result in severe damage to downstream equipment and pose significant hazards to occupants and property.