Textbook 1: Electrical Systems and Materials: Service and Utilization (Chapter 27 Summary) PDF

Textbook 1 Electrical Systems and Materials: Service and Utilization. Chapter 27 Summary 1239-1298 Chapter 27 Electrical Systems and Materials: Service vand Utilization Electric service is how electricity is brought into a building. 27.1 ELECTRIC SERVICE...

Textbook 1 Electrical Systems and Materials: Service and Utilization. Chapter 27 Summary 1239-1298 Chapter 27 Electrical Systems and Materials: Service vand Utilization Electric service is how electricity is brought into a building. 27.1 ELECTRIC SERVICE The Codes and Standards that apply to electric ser vice include: National Electrical Code (NEC): Provides rules for electrical installations. National Fire Protec tion Association; in particular, (Section 230 is key). National Electrical Safety Code: Covers safety for overhead and underground lines, grounding, and more. Utility Standards: Utilities have their own guidelines for connecting service to buildings. In the U.S., public utilities must provide service up to the edge of a private property. Connection Point: The utility connects their lines at or just beyond the property line. Types of Connections: Overhead Drop: Service comes from a utility pole above the ground. Underground Service: Service comes from underground lines to the building. Owner’s Cost: The property owner usually pays for the electrical work needed from the property line to their building. Sometimes, property owners can help decide how electricity is brought to their site, especially in large developments or if they’re willing to share costs for better service. Utilities often have programs to improve the look of their equipment. The way electricity is delivered to a building (overhead or underground) depends on: -Distance: How far the electricity needs to travel. - Ground Type: The kind of land or soil. -Cost Sharing: Whether the owner helps pay for the installation. - Power Needs: The amount of electricity required. -Appearance: How important the look of the service is. - Local Rules: Local practices and regulations- -Maintenance: How easy it is to maintain the service. - Weather: Local weather conditions. -Building Setup: How electricity is distributed within the building. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.2 OVERHEAD SERVICE Overhead electric lines are cheaper for utilities to install, saving between 10% and 50% compared to underground lines. That’s why most installations are overhead. However, new methods have made underground lines more affordable and a good option in some cases. For long distances (hundreds of feet or more) or high voltages (over 5000 V), overhead lines are often used because they’re cheaper and easier to maintain. Underground lines are costly and less practical in rocky terrain or heavy electrical loads. When to Use Overhead vs. Underground Lines: Overhead Lines: Best for long distances, high voltages, and where maintenance is easier. Underground Lines: Better for areas with severe weather (snow, wind, ice) or where even short outages are problematic. 27.2 OVERHEAD SERVICE Types of Overhead Cables: Bare Cables: Used for high-voltage lines, supported on insulators. Weatherproof Cables: Used for low-voltage lines, mounted on racks. Preassembled Aerial Cables: Bundled, insulated cables for voltages up to 15 kV, often more cost-effective and weather-resistant. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.3 UNDERGROUND SERVICE Benefits: Looks Neater: No overhead wires or poles. More Reliable: Less affected by weather or accidents. Lasts Longer: Generally has a longer lifespan. Drawback: Expensive: Costs more than overhead lines. Cost-Saving Option: Direct Burial: Cheaper method where cables are buried directly without extra protection. However, if the cable fails, repairs are more difficult and time-consuming. Factors to Consider: Cost: Extra expense for installation and maintenance. Outage History: Frequency of problems with direct burial cables in the area. Repair Costs: Cost and availability of fixing issues. Service Impact: Time and cost to fix outages, including digging up lawns or paved areas, especially for businesses. Underground wiring requires specially designed and approved cables. Type SE: Basic service cable, moisture and flame-resistant. SE type U or (USE): For underground use, with extra moisture protection. Type UF: For underground feeder cables used in other applications. A typical detail of an overhead electric service entrance to a multiresidence building is shown in Fig. 27.2 Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.4 UNDERGROUND WIRING The first alternative offers Low Cost, Easy to Install: Pros: Cheapest and simplest to set up. Cons: Difficult and costly to repair if something goes wrong The second offers high strength and permanence, but at the highest price of the three. The last offers median Cost, Less Strength: Pros: Moderately priced. Cons: Not very strong; best for undisturbed ground or light paving. Nonmetallic duct (conduit) intended for under ground electrical use is commercially available in two wall thicknesses. Types of Conduit: Type II: Thick, strong wall, used directly buried without concrete. Type I: Thinner wall, needs at least 2 inches (50 mm) of concrete around it. Such ducts may be manufactured from a variety of materials and are sold under several trade names Plastic conduit (PVC) or simply plastic. Nonmetallic conduit common and cost-effective; used without concrete for low-voltage wiring and with concrete The methods available for for high-voltage wiring. It’s less expensive and doesn’t corrode like metal\steel conduit. underground wiring are: Direct burial (Fig. 27.3) Installation in Type I, For long underground wiring runs, a pulling handhole or manhole is needed to assist with installation. concrete‐encased duct (Fig. 27.4a) Installation in Type Access Points: II, direct burial duct (Fig. 27.4b). Handholes: Small access points for low-voltage cables. Manholes: Larger access points for high-voltage cables and large ducts. Precast handholes and manholes: Ready-made and usually cheaper than field‐formed and poured units. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.7 TRANSFORMERS OUTDOORS While exterior installations have benefits, finding suitable indoor space, like a basement, is often easier. Noise and high costs for long voltage runs can be issues with exterior setups. Heat from transformers can be managed with ventilation. Exterior transformers need shading from the sun and are less ideal in vandal-prone areas. Aesthetics can be a concern, though manufacturers offer designs to address this. The most common exterior type is the pad-mounted transformer, which is easy to install on a concrete pad. 27.8 TRANSFORMERS INDOORS: HEAT LOSS Indoor transformers generate significant heat—about 1% to 1.5% of their load rating. For example, a 750- kVA transformer with a 150°C rise generates 12 kW (41,000 Btu/h) of heat at full load. To avoid overheating, especially if heat can't be reused, ensure adequate ventilation to keep the room temperature below 40°C (104°F). 27.9 TRANSFORMERS INDOORS: SELECTION Indoor transformer installations must comply with NEC regulations for safety, as outlined in NEC Article 450. Key considerations are summarized here. (a) Oil‐Insulated Transformers (b) “Less‐Flammable” Liquid‐Insulated Transformers Oil-filled transformers pose a fire risk indoors due to potential leaks, Transformers up to 35 kV with "less-flammable" liquids (fire point ≥ requiring costly fire-resistant vaults (exceptions are in NEC Article 450). 300°C/572°F) can be installed indoors without a vault, but require a Despite this, they offer benefits like compact size, low initial cost, low liquid confinement area and fire safety measures. They offer similar losses, long lifespan, excellent performance, low noise, and high overload benefits to oil-insulated units, often at a lower cost. capacity, making them suitable for industrial facilities. Chapter 27 Electrical Systems and Materials: Service vand Utilization (c) Nonflammable Fluid‐Filled Transformers Old nonflammable liquid coolants, like PCBs, were widely used but are now banned due to environmental concerns. New nonflammable coolants are more expensive, and while they offer similar benefits to oil-filled units, they often need a sump or catch basin and can be costly. (d) Dry‐Type Transformers Indoor transformers are popular despite having shorter lifespans, higher losses, more noise, and greater size compared to liquid-filled units. They are favored for their easy installation and flexible placement. Using a higher-rated transformer can reduce heat and extend its life, and noise can be lowered for an extra cost. Table 27.4 compares the costs of different transformer types. 27.10 TRANSFORMER VAULTS A transformer vault is a fire-rated enclosure needed because oil-filled transformers can pose a fire risk if they fail. While transformers are durable and reliable, they can be a fire hazard. Vaults should be ventilated with outdoor air and have at least 3 in²/kVA (1935 mm²/kVA) of opening area, or at least 1 ft² (0.09 m²). For more details, refer to NEC Article 450. 27.13 SWITCHES Traditional switches open and close circuits by moving electrical contacts. They can be operated manually, electrically, by a spring, or a motor. Solid-state switches, which have no moving parts, perform the same function using a different process. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.14 CONTACTORS 27.15 SPECIAL SWITCHES - Contactor Definition: A contactor is an electrically operated switch that Special Switches: Many types exist, but only a few are relevant for uses silver-coated copper contact blocks to open or close a circuit. building design. - Operation: Unlike manual switches, contactors are usually operated by 1. Remote-Control (RC) Switches: an electromagnet. They close contacts when energized and open them by - A type of contactor that latches mechanically after being operated. spring action or gravity when de-energized. - Differs from relays by latching contacts and disconnecting the electric - Types of Contacts: circuit. - To unlatch, the circuit must be reenergized, so it’s also called an - Normally Open (NO): Contacts are open when de-energized. electrically operated mechanically held contactor. - Normally Closed (NC): Contacts are closed when de-energized. - Useful for maintaining contact positions over long periods, e.g., in lighting - Motor Starters: Contactors designed for motor connection are called control circuits, without needing continuous coil energization. motor starters. - Commonly used for controlling large loads like exterior or whole-building lighting. - Remote Control: Contactors allow for remote control and automation, 2. Automatic Transfer Switch: unlike switches which are manually operated. They can be controlled by - Critical component for emergency and standby power pushbuttons, timers, thermostats, etc. systems. - Applications: Used in lighting, heating, air conditioning, motors, and similar control functions. - Advantage: The ability to be remotely controlled makes contactors ideal for a wide range of automated systems. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.17 EQUIPMENT ENCLOSURES C- Characteristics of Fuses and Circuit Breakers 1. NEMA Enclosures: - Proper nomenclature, descriptions, and applications can be found in Table 27.5. 2. Weatherproof Enclosures: - No official "weatherproof" (WP) enclosure exists, but there are specific enclosures for outdoor protection: 1. Type 3R: Protects against rain. 2. Type 3S: Protects against wind-driven rain and sleet. 3. Type 4: Protects against rain, wind-driven rain, sleet, splashing, and condensation. 3. Type 12 Industrial Enclosure: - Similar to Type 1 but gasketed for dust and drip resistance, making it ideal for dirty indoor environments such as commercial and institutional spaces. 27.19 SWITCHBOARDS AND SWITCHGEAR A unit substation is a system that takes high-voltage electricity, reduces it to a safer voltage, and distributes it within a building. It has high-voltage switches, a transformer, meters, controls, and low- voltage equipment. The terms switchboard and switchgear are often confused, but they usually mean different things. Switchboards are for low-voltage systems and can include big circuit breakers. Switchgear is for high-voltage equipment (over 600 V). When switchboards use molded-case circuit breakers, they are often called building-type switchboards. Chapter 27 Electrical Systems and Materials: Service vand Utilization Modern switchboards are designed to be safe, with all live parts enclosed in a metal box. Operators control them using pushbuttons and insulated handles on the front. Some switchboards have circuit breakers that slide in and out like file drawers, making it easy to replace them in emergencies. While switchboards are for low voltage, switchgear is for high voltage (over 600 V). Building-type switchboards use molded-case circuit breakers. Switchgear needs specific space and must follow safety regulations. Main switchgear is often installed in basements with ventilation, while smaller switchboards can be in open areas with safety signs. Architects must ensure there are enough exits and space for installing and removing equipment. For outdoor switchgear, options include building a shelter, using weatherproof gear, or choosing gear with its own housing, which often includes heating and lighting and can be more cost-effective. Switchgear needs enough space around it and must follow safety guidelines. In large buildings, it's usually located in a well-ventilated basement. Smaller switchboards don’t require a special room but should be enclosed with a wire screen and have a “DANGER—HIGH VOLTAGE” sign. Building plans should account for space to install and remove equipment. For outdoor switchgear, you can build a small shelter for indoor equipment, use weatherproof gear, or choose switchgear with its own outdoor enclosure, which often includes heating and lighting and is usually the most cost-effective option. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.20 UNIT SUBSTATIONS (TRANSFORMER LOAD CENTERS) A unit substation, also called a load-center substation, is a setup that includes a high-voltage switch and fuse or circuit breaker, a step-down transformer, meters, controls, buswork, and low-voltage switchgear. It takes high-voltage power from an incoming supply, reduces it to a usable lower voltage, and then distributes that low-voltage power within the facility. 27.21 PANELBOARDS Equipment can be installed indoors or outdoors. Indoor unit An electrical panel, or panelboard, is like a smaller substations usually use dry-type (air-filled) transformers, switchboard. It takes in a lot of power and splits it which are safe for indoor use. These substations are often into smaller sections for distribution. It has main located in basements with specific ventilation needs and buses and circuit breakers or fuses that connect to limited access for authorized personnel only. The choice of smaller circuits. Panelboards are usually the final unit substations is based on the advantages of using step in distributing power to things like lights and prefabricated, coordinated parts. motors. In homes, small panels are often called load centers. Panelboard parts, like buses and breakers, are stored in a metal box called a backbox. This backbox has openings for conduit connections and main power feeds. Some panels have a main circuit breaker to shut off the whole panel during a major issue, while others, called “lugs in mains only,” only have connectors for feeder cables and no main breaker. The backbox is covered with a front panel that has a door for access. Chapter 27 Electrical Systems and Materials: Service vand Utilization Some receptacles come with built-in features for extra protection. Ground-fault circuit interrupter (GFCI) receptacles protect against electrical shocks and are discussed in Section 29.4. Isolated ground receptacles, marked with an orange triangle, help reduce electrical noise and are connected to a separate ground wire to minimize interference. Additionally, some receptacles include surge suppression to protect devices from voltage spikes. Solid-state switches are available with high/off/low settings for incandescent lamps and cost only a bit more than regular switches. They’re great for places where you need adjustable lighting to save energy. In high-security areas, you can use a tumbler lock switch instead of a 27.30 WIRING DEVICES: SWITCHES standard key switch. Timer switches can control devices like bathroom heaters and fans. Modern programmable switches fit into wall boxes and can do multiple tasks, like dimming and Switches that fit in outlet boxes can handle remote operation. Newer dimmers can also work with fluorescent lamps and have fewer up to 30 A and come in types rated for 15, problems with radio interference. 20, or 30 A at 120 or 120/277 V. AC-only switches are usually more durable. Common types include single-pole, 2-pole, 3-way, and 4-way, with handles that can be toggle, push, rocker, or rotary. Some switches are quiet, like mercury types, while others, like toggles, are noisier. For example, a switch might be a single-pole, AC, quiet type rated for 15 A at 120 V with lighted press handles. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.32 LOW‐VOLTAGE SWITCHING In systems with built-in flexibility, you can monitor - Full-Voltage Switches: Operate directly at line voltage and full current, connected to the individual loads from a central control panel using load circuit. - Low-Voltage Switching: Uses a control scheme where switches operate at a lower relays with extra contacts. This is crucial for energy voltage than the load circuit. This involves: conservation since relying on manual controls alone - Control Circuits: Low-voltage switches control the high-voltage circuits through a often doesn’t work well. Basic system components separate low-voltage control circuit. include control relays and switches. - Reduced Current: The low-voltage switches manage the circuit without handling full load currents directly. This approach enhances safety, reliability, and flexibility in controlling high-voltage systems. Low-Voltage Switching - Description: Uses 24-V light-duty switches to control line voltage relays, known as low- voltage switching or remote-control switching. - Control Capabilities: - Flexibilit: Supports local, remote, and master control with overrides from devices like occupancy sensors and central controls like timers. - Wiring Benefits: Costs less than full-voltage wiring due to lighter wiring needs. - Advantages: - Flexible control locations. - Individual load control. - Group load control. - Lower wiring costs. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.34 POWER LINE CARRIER SYSTEMS Flexible, programmable load-switching systems help manage energy, but their high costs make them impractical for large buildings. Wiring can be very expensive, sometimes over half the total cost. To save on wiring, a power line carrier (PLC) system was created. This system uses existing power lines to send control signals, so no extra wiring is needed. It’s easy to add or remove, making energy management more affordable. The system sends low-voltage, high-frequency signals through the power lines. Receivers pick up these signals and control devices like lights (turning them on, off, or adjusting brightness). The control can be a simple manual switch for homes or a computer-based system for businesses. There are four main types of receivers. 1.Wall-switch module: Acts like a regular light switch but also includes a receiver and relay. 2.Wall receptacle module: A power outlet with a receiver and relay to switch power. 3.Switching module: Used to control contactors or small motors. 4.Dimming module: Controls both light intensity and can be managed remotely. 27.35 POWER CONDITIONING (a) General Information Power conditioning takes utility power, which can have surges, spikes, noise, and voltage changes, and makes it stable and clean, often called computer-grade power. This is important for data processing, telecommunications, and sensitive electronics because it prevents data errors, overheating, and equipment failures. While power conditioning is different from uninterruptible power supplies (UPS), some systems combine both functions. (b) Sources of Disturbance Utility power systems try to keep voltage and frequency stable over time, but they can’t fix short-term issues that affect electronics. These issues include: 1.Voltage Variations: Slow, lasting changes caused by things like motor starts, brownouts, and load switching. 2.Electrical Noise: High-frequency, low-power voltages that distort power, coming from equipment like power supplies and dimmers. 3.Transients: Brief, high-voltage spikes from lightning or system faults, which can cause major equipment failures. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.36 POWER‐CONDITIONING EQUIPMENT 27.38 UNINTERRUPTIBLE POWER SUPPLY Types of Problems & Solutions Uninterruptible Power Supply (UPS) 1.Voltage Variations: Fix with voltage regulators. -Purpose: Provides backup power to prevent data loss and equipment 2.Noise Issues: Use electrical isolation, filtering, and noise suppression. problems during power outages, keeping important devices like 3.Transients: Use surge suppressors to reduce effects. computers and servers running. -Transfer Time: UPS systems switch to backup power in 8.3 Recommendations milliseconds (ms) or less, which helps avoid computer issues and 1.Computer Installations: Use good surge suppressors; avoid cheap plug-in meets industry standards. strips. -Compliance: This transfer time is double what’s required by IEEE 2.Major Data-Processing Installations: Use an integrated power-conditioning Standard 446, ensuring it follows strict guidelines for reliable power unit for full protection. in the computer industry. 3.Separate Feeders: Improve power quality by using separate feeders for sensitive equipment. 4.Physical Isolation: Keep sensitive equipment away from disturbance sources, like certain lights. 5.Isolated Ground Receptacles: Use color-coded outlets for better grounding and reduced noise, especially with dimmers. 6.Harmonics and Noise: Address issues from equipment that creates harmonics, which can overload the system. Design Considerations - Get a detailed power quality report from the utility about outages, voltage stability, and waveforms. - Conduct a power-quality study at the facility using specialized tools and experts. Chapter 27 Electrical Systems and Materials: Service vand Utilization (a) Engine–Generator Sets 27.39 EMERGENCY/STANDBY POWER EQUIPMENT An engine-generator set has three main parts: the fuel system, the generator, and its installation space. The NEC distinguishes between emergency systems and standby systems. Benefits: - Emergency Systems: Power critical safety equipment like exit - Unlimited power capacity lights and fire alarms during outages. - Long running time based on fuel tank size - Standby Systems: Required for essential processes (like HVAC - Potential for continuous use with good maintenance and water supply) or optional to protect equipment and property from financial loss. Drawbacks: NFPA Standard 110 outlines the equipment requirements for - Noise and vibration both systems. - Exhaust issues - Regular maintenance required - Fuel storage challenges: Health-care facilities must follow NEC Article 517 and NFPA - Gasoline has a short storage life and is difficult to dispose of. Standard 99, enforced by local, state, and federal codes. - Diesel lasts longer but is also hard to dispose of. Authorities decide on the need for emergency and standby - Natural gas avoids storage issues but relies on a stable supply during systems. NEC provides design guidelines, but installation depends emergencies. on these codes. Exit lighting is required by NFPA and OSHA, not - Steam may be available in some cities, but its reliability in outages should be NEC. Emergency systems are generally required, while standby verified. systems are needed only for critical functions like water treatment, with optional systems often using fuel-based generators. (b) Battery Equipment Storage batteries provide emergency power, especially for lighting and UPS systems. Common types include lead-acid, nickel-cadmium, and alkaline. They are typically installed in cabinets or racks with automatic chargers. The battery choice depends on the specific needs of the setup. Installation requirements, like ventilation and gas detection, vary by battery type and size. For more details, follow NEC Article 480 and consult a battery expert. Chapter 27 Electrical Systems and Materials: Service vand Utilization 27.40 SYSTEM INSPECTION Inspection Process: 1.Initial Inspection: After raceways are installed but before wiring is finished and walls are closed. 2.Final Inspection: After the entire electrical system is installed. Purpose: To ensure compliance with national and local codes and verify that the design, materials, and installation meet standards. Responsibilities: - Contractor: Ensures quality installation. - Designer: Must understand installation practices and equipment to create feasible designs. They should also track equipment substitutions to ensure specified equipment is supplied. Batteries can be located centrally or in small units throughout a building. Commissioning: Central systems typically provide 24 to 125 V for emergency lighting, Align electrical systems with the Owner’s Project Requirements for while individual units supply AC power via inverters. They have limited proper functionality and compliance. power duration and environmental concerns when disposed of. NEC requires batteries to support loads for at least 1½ hours, but larger capacities are often used.