Electrical Design Chapter 9 (PDF)

Chapter 9 Electrical Design Chapter 9 Electrical Design..................................................................................... 9-1 9.1 Key Terms.................................................................................................................... 9-1 9.1.1 Abbreviations............................................................................................................................................9-1 9.1.2 Definitions..................................................................................................................................................9-3 9.2 General Information................................................................................................... 9-4 9.2.1 SPU Facility Types....................................................................................................................................9-4 9.2.2 Electrical Design Considerations......................................................................................................... 9-4 9.2.3 Electrical Design Elements..................................................................................................................... 9-6 9.2.4 DGS Design Resources.......................................................................................................................... 9-9 9.3 General Requirements.............................................................................................. 9-10 9.3.1 Industry Codes...................................................................................................................................... 9-11 9.3.2 Regulations.............................................................................................................................................. 9-11 9.3.3 Industry Standards................................................................................................................................ 9-11 9.4 Design Process........................................................................................................... 9-12 9.4.1 Design Checklist.................................................................................................................................... 9-12 9.4.2 Responsibilities of Electrical Design Engineer................................................................................ 9-13 9.4.3 Electrical Design Documents............................................................................................................. 9-14 9.5 Design Guide.............................................................................................................. 9-16 9.5.1 Reliability and Redundancy................................................................................................................. 9-17 9.5.2 Environmental Materials and Equipment Location....................................................................... 9-18 9.5.3 Voltage..................................................................................................................................................... 9-27 9.5.4 Wiring and Protection......................................................................................................................... 9-28 9.5.5 Raceway Systems [Spec 26 05 33].................................................................................................... 9-45 9.5.6 Emergency and Standby Power Systems......................................................................................... 9-56 9.5.7 Transfer Switches [Spec 26 63 00]................................................................................................... 9-59 9.5.8 Lighting Systems [Specs 26 51 00 & 26 56 00].............................................................................. 9-59 9.5.9 Special Systems...................................................................................................................................... 9-64 9.5.10 Major Electrical Equipment................................................................................................................. 9-66 9.6 Resources................................................................................................................... 9-89 Appendices Appendix 9A - Standard Specifications for Electrical Design Appendix 9B - Standard Drawings for Electrical Design Appendix 9C - Design Calculations for Electrical Design Appendix 9D - SPU Electrical Design Checklist Appendix 9E - Basis of Electrical Design Memorandum List of Figures Figure 9-1 Basis of Design Plan Sheet Data for Electrical Design........................................................................9-14 List of Tables Table 9-1 Electrical Codes for SPU Electrical Design.............................................................................................9-11 Table 9-2 Industry Standards Organizations..............................................................................................................9-12 Table 9-3 Simplified Checklist for Electrical Design................................................................................................9-13 Table 9-4 Coordination Matrix for Electrical Design..............................................................................................9-15 Table 9-5 Typical Applications of Redundancy.........................................................................................................9-18 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-i Chapter 9 Electrical Design Table 9-6 Other Standards for Classifications of Hazardous Areas....................................................................9-19 Table 9-7 Environmental Conditions and Materials Applications Master Table...............................................9-22 Table 9-8 Corrosion Resistance...................................................................................................................................9-25 Table 9-9 Mounting Heights for SCADA Equipment and Devices......................................................................9-26 Table 9-10 Electrical System Voltage Nomenclature (United States).................................................................9-27 Table 9-11 Medium and Low-Voltage System Protective Devices......................................................................9-30 Table 9-12 Recommended 3-Phase Feeder Sizes for Copper Conductors1.....................................................9-32 Table 9-13 Class I and Class II Materials....................................................................................................................9-44 Table 9-14 Illuminance Categories...............................................................................................................................9-60 Table 9-15 Insulation System Classification...............................................................................................................9-71 Table 9-16 Low-Voltage Transformer Feeder and Breaker Sizing for Copper Conductors (3-Phase, 480V Primary and 208Y/120V Secondary)............................................................................................................................9-72 Table 9-17 Motor Control and Feeder Data (460V, 3-Phase, 60 Hz Motors).................................................9-80 9-ii SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design Chapter 9 ELECTRICAL DESIGN This chapter of the Design Standards and Guidelines (DSG) presents standards and guidelines for electrical design for Seattle Public Utilities (SPU) facilities. It includes master electrical specifications, standard drawings, and design calculations. The primary audience for this chapter is SPU electrical engineers and team members working on SPU infrastructure-related projects. DSG standards are shown as underlined text. As SPU’s first comprehensive electrical design document, this chapter is also intended to establish a historical baseline reference for typical electrical facilities and components. This information, used in conjunction with engineering judgment, appropriate codes, national standards, and other reference information, will ensure electrical systems that are safe and suited for the intended application. This DSG does not replace the judgment of an experienced, licensed Professional Engineer (PE). All electrical design for SPU infrastructure should be done under the supervision of an experienced, licensed PE. 9.1 KEY TERMS Abbreviations and definitions given here follow either American usage or regulatory guidance. 9.1.1 Abbreviations Abbreviation Term A amp AC alternating current ADA Americans with Disabilities Act AHJ Authority Having Jurisdiction ANSI American National Standards Institute AWG American wire gauge BKR breaker CBD cable block diagram CCTV closed-circuit television CF compact fluorescent CKT circuit CRI color rendition index or color rendering index CSI current source inverter SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-1 Chapter 9 Electrical Design Abbreviation Term CSO combined sewer overflow CT current transformer DC direct current EMT electrical metallic tubing EPDM ethylene propylene-diene monomer EPR ethylene-propylene rubber FLA full-load amps FRP fiber-reinforced plastic ft feet G grounding HID high-intensity discharge hp horsepower HPS high-pressure sodium HVAC heating, ventilation, and air conditioning I&C instrumentation and control ICS industrial control systems IMC intermediate metal conduit kcmil thousands of circular mils kV kilovolt kVA kilovolt ampere LEL Lower Explosive Limit LOR Local Off Remote MCC motor control center MCP motor circuit protectors MH metal halide MOV metal oxide varistor NEC National Electrical Code NEMA National Electrical Manufacturers Association NRTL Nationally Recognized Testing Laboratories OSHA Occupational Safety and Health Administration PAC programmable automation controller PLC programmable logic controller PWM pulse-width modulated 9-2 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design Abbreviation Term PVC polyvinyl chloride RCM reliability centered maintenance RGS rigid galvanized steel RMC rigid metallic conduit RMS root mean square RNC rigid non-metallic conduit RTD resistance temperature devices SAD silicon avalanche diode SCADA supervisory control and data acquisition SCL Seattle City Light SPD surge protective device SST stainless steel TSP twisted shielded pair TST twisted shielded triad UL Underwriters Laboratory UV ultraviolet V volt VA volt ampere VAR volt ampere reactive VFD variable frequency drive VVI variable voltage inverter XLPE cross-linked polyethylene 9.1.2 Definitions Term Definition codes Refers to the legal documents whose use is determined by the jurisdictions governing a project or electrical manufacturing industry codes. Codes are typically geographically dependent. guidelines Advice for preparing an engineering design. Guidelines document suggested minimum requirements and analysis of design elements to produce a coordinated set of design drawings, specifications, or lifecycle cost estimates. Design guidelines answer what, why, when and how to apply design standards and the level of quality assurance required. See also standards. references In this DSG chapter on Electrical Design, references are sources of content and include sufficient detail (e.g., document, section and table number, and/or title) that the user can easily refer to the source. The National Electrical Code (NEC) and National Electrical Manufacturers Association (NEMA) documents are frequent references in this chapter. SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-3 Chapter 9 Electrical Design Term Definition regulations Legal design standards that must be incorporated into the design. Examples include Occupational Safety and Health Administration (OSHA) requirements, the Americans with Disabilities Act (ADA), etc. reliability A process used to determine what must be done to ensure that any physical asset continues centered to do what its users want it to do in its present operating context. maintenance (RCM) standards This DSG chapter on Electrical Design is an exception to the strict application of the word “standard.” Because electrical design follows long-established industry standards, we have used the definition of standard in item #1 below. 1. Opinions and recommendations that form design guidelines that are not legal in nature but are considered a standard of practice. Standards are often published by industry associations but may also be established by SPU. See also guidelines. 2. For the DSG, the word standard, refers to the following: drawings, technical or material specifications, and minimum requirements needed to design a particular improvement. A design standard is adopted by the department and generally meets the functional and operational requirements at the lowest lifecycle cost. It serves as a reference for evaluating proposals from developers and contractors. For a standard, the word must refer to a mandatory requirement. The word should is used to denote a flexible requirement that is mandatory only under certain conditions. 9.2 GENERAL INFORMATION SPU electrical engineering design is project specific and applied to a variety of facility types. The role of the electrical design engineer varies accordingly. This section provides general background information on SPU facility types, electrical design elements, and design resources. 9.2.1 SPU Facility Types SPU builds, operates, and maintains all water, wastewater, and solid waste facilities for the City of Seattle (the City). These include two large water treatment plants at the Tolt and Cedar watersheds, which private companies operate under long-term contracts. SPU’s support facilities include offices, operations centers, maintenance facilities, and labs. For more information, see the relevant chapters in this DSG for each type of facility. 9.2.2 Electrical Design Considerations This section describes basic electrical design considerations for SPU facilities. 9.2.2.1 Facility Related A. Type The driving force behind every electrical design is the need to provide power for a particular purpose. For SPU, that purpose is determined by the type of facility. Factors that affect electrical design are a facility’s purpose (e.g., whether it manages water or wastewater), age, upgrade history, capacity, and physical layout. For example, a water 9-4 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design pump station will likely require large motor-driven pumps, while a flow monitoring vault will require minimal power. B. Loads Facility loads (e.g., motors and lights) are users of electrical power and form the basis for calculating the size of an electrical system. Utility service and feeder sizes are based on National Electrical Code (NEC) and serving utility’s requirements. The following items affect calculations: Size of the largest motor Heating, ventilation, and air conditioning (HVAC) and lighting loads Future expansion provisions Motor starting methods Unit process equipment C. Importance A facility’s importance is measured by the consequences of its failure to function. Loss of electrical power to SPU facilities could range from a minor consequence (e.g., loss of non-critical information) to a major consequence (e.g., threat to human life or property). Electrical design will often have to consider either on-site or portable backup power. At present, there are only two cost-effective choices for sources of backup power: engine-generators and batteries (uninterrupted power supply). D. Reliability Reliability is a measure of the expected operational availability for an electrical system. The need for reliability is linked to a facility’s importance and ease of maintenance. Although it is beneficial to have highly reliable systems at all times, it is costlier to design, build, and maintain such systems. The main way to increase reliability is to provide parallel or redundant components or systems so that a single failure will not disable the facility. For SPU reliability requirements, see DSG section 9.5.1. E. Environment The type of SPU facility determines the environment in which electrical system components function. For example, wastewater pump stations have hazardous and corrosive conditions, while water pump stations have non-hazardous and dry conditions. Dry conditions, such as an electrical room or weatherproof enclosure, should be provided for most electrical gear. Some decisions affected by environmental conditions are enclosure National Electrical Manufacturers Association (NEMA) ratings, electrical materials selection, and installation methods. F. Construction Construction design and methods influence electrical design in two ways: 1. Constraints and accommodations of the facility structure 2. Materials and installation choices available to the structure SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-5 Chapter 9 Electrical Design Reduced material costs must be balanced against flexibility. Other factors to consider are available space and constructability. For example, a utility meter can often be installed in a switchboard lineup, but sometimes space is too tight and it is better to install a meter outside. As another example, a motor control center (MCC), though larger, is often a better fit for a tight space than individual controls. G. Maintenance SPU takes a reliability centered maintenance (RCM) approach to determine what must be done to ensure that any physical asset continues to do what its users want it to do in its present operating context. This approach requires operation staff to define and describe their specific methodology related to the level of maintenance. 9.2.2.2 Safety Safe electrical design is paramount. The electrical design engineer needs to be aware of the multiple sources and issues that affect project safety. Selecting listed and labeled equipment appropriate to function is only one consideration. Other safety considerations include where and how equipment is installed, as the environment determines how safely SPU Operations staff can interact with the equipment. Limiting access for unqualified persons protects the public, and selecting non-toxic materials is safer for the environment. 9.2.2.3 Location and Social Issues Most SPU facilities are located in populated areas. In these areas, visual and other characteristics of the facility may negatively affect a neighborhood. Serious consideration should be given to reducing the visual footprint of the facility and its electrical service by placing them underground. Even underground, the generation of noise or odors cannot be ignored. When aboveground, equipment should be selected for quiet operation and generators should have a silencer and critical grade muffler. Any outside lights should be full cutoff and positioned to minimize spillover into the neighborhood. 9.2.2.4 Local Utilities The electrical design engineer must inform local utilities of a project’s needs and incorporate the utilities’ requirements into electrical design, including power, communication, water, and sewer. 9.2.3 Electrical Design Elements This section describes basic elements for electrical design of SPU facilities. 9.2.3.1 Power Most SPU projects require one or more of the following power types: 240/120 volt (V) 1-phase 240/120V 3-phase open delta 208/120V 3-phase 480/277V, 3-phase 4,160/2,400V, 3-phase 9-6 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design From the local utility (usually Seattle City Light [SCL]), 480V services are 480/277V, 4-wire with a solidly grounded neutral wire at the main service breaker. Most 3-phase loads do not use a system neutral wire. For most facilities with emergency power, the neutral is carried through to a transfer switch for connection to a generator neutral. A step-down transformer provides 120V power. Unless 240V power is required, a 208V/120V, 3-phase step-down transformer should be used. Service size (ampacity) is usually 100 amps (A) for 1- phase and 200A or greater for 3-phase. Services above 225A should be configured with a current transformer (CT) enclosure and separate meter-base according to utility requirements. Large facilities with a switchgear lineup may include a service entrance and metering section. The usual alternate power source for SPU facilities is a diesel-powered standby generator (genset). It may be permanently installed on-site at critical facilities or there may be provisions for connecting a portable genset. Critical SPU facilities often have both. Smaller facilities may use propane as the fuel source. 9.2.3.2 Codes For a list of the codes that govern electrical design for SPU facilities, see DSG section 9.3. 9.2.3.3 Loads The loads for a project are usually divided into two types: Process (loads fulfilling the purpose of the facility) Facility (loads necessary to keep the process loads functioning) At SPU facilities, the main process loads are motors that drive pumps (see DSG Chapter 11, Pump Stations for typical pump requirements). Compressors, blowers, and fans compose the bulk of the other motor-driven loads. Unit process loads such as ultraviolet (UV) or ozone generation are also large users of electric power. Electrical heaters for air and water are the largest facility loads, with lights, receptacles, and special systems usually constituting less than 10% of the total load. 9.2.3.4 Lighting Most SPU facilities require some combination of the following types of lights: Light emitting diode (LED). SPU prefers LED lighting applications used in new and retrofit facilities and in outdoor/indoor, wet/corrosive, and hazardous/non-hazardous areas. Tube fluorescent. T5 or T8 4-ft tubes are used in open fixtures with reflectors, with a few uplights, or in enclosed and gasketed fixtures for wet/corrosive areas. Compact fluorescent (CF). SPU uses these bulbs in most outdoor and hazardous location fixtures where instant-on lights are required. High-intensity discharge (HID). Bulbs that are either high-pressure sodium (HPS) for highest efficiency or metal halide (MH) for best color rendition are used in outdoor wall- or pole-mounted fixtures. They are also used in large and high-ceiling indoor areas. HID fixtures take several minutes to achieve full brightness. SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-7 Chapter 9 Electrical Design 9.2.3.5 Instrumentation & Control For details on instrumentation and control (I&C), see DSG Chapter 10, I&C (Supervisory Control and Data Acquisition [SCADA]). I&C equipment is located on the electrical drawings and installed by an electrical contractor. Most existing SPU SCADA systems depend on telephone lines. The electrical design engineer is usually responsible for coordinating with an SPU SCADA engineer and a local communications company to bring the service to the site and for identify and show the demarcation point. The electrical power system supplies power for the instruments, control devices, and control panels. The power source for instruments, whether from a 120V circuit breaker panel or a main I&C control panel, is one of the early design coordination decisions. It is preferable to supply the instrument power from the control panel unless space is limited. Testing is facilitated by having both power and signal wires accessible in the same place. It is the electrical design engineer’s responsibility to translate the control requirements for the process equipment into elementary (control) diagrams. The electrical design engineer should also ensure that the necessary signals are provided among the electrical starters, I&C control panel, and SCADA system. These signals are either discrete (on/off) or analog (continuously variable over a specified range) and fall into two general categories: status or alarm. Status signals provide information about the state of something, whether ON or OFF, while alarm signals require attention. A trouble signal falls in between status and alarm, indicating a potential or future problem. Critical control, including safety interlock circuits and security signals, must be a fail-safe circuit. The following are typical SCADA status signals: Flow rate (analog) Fuel tank low level Genset power available Pump fail Pump on/run Transfer switch position Utility power fail Valve closed Valve open Valve position (analog) Wet well level Flood switch Hazard gas LEL (analog) Intrusion switch The following are typical control signals: START/STOP (for pump) OPEN/CLOSE (for valve) 9-8 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design 9.2.3.6 Special Systems A. Fire Alarm Most SPU facilities do not have a distinct fire alarm system. They have fire detection devices, such as smoke detectors or heat sensors, which send alarm signals to the SCADA system via a main control panel. If a complete fire alarm system is required, it is specified as contractor designed and Authority Having Jurisdiction (AHJ) approved. The electrical designer must show an acceptable location on the drawings for the fire alarm panel and provide power to it. For remote monitoring services, the connection to the telephone interface board must be shown. Any auxiliary devices (duct smoke detectors or fire dampers) must be shown with power and control wiring. B. Security The basic SPU security concern is unauthorized intrusion into a facility. While access and acknowledge switches have been adequate, there is a growing need for additional measures. Some additional measures include closed-circuit television (CCTV), access control systems (ACS), and intrusion detection systems (IDS) with specialized devices. The degree of security should be coordinated with the project manager in coordination with SPU’s Security and Emergency Management staff for site specific scopes. For additional details on security, see DSG Chapter 15, Physical Security. C. Telephone and Data Most SPU projects need at minimum a dial-up telephone line for alarm transmission and communication. SCADA also requires a dedicated telephone line or direct connection to the water or wastewater network. The electrical designer should coordinate with the Project Manager (PM) and SPU SCADA Engineer to install fiber or cellular communication where feasible, as physical telephone lines are being phased out. Specific requirements should be coordinated with I&C and Field Operations and Maintenance (O&M). D. Lightning Protection Most SPU projects do not require lightning protection. Water tanks and other elevated and exposed structures like antenna towers should be evaluated and documented if a lightning protection system is not implemented. Seattle does experience occasional severe lightning storms. 9.2.4 DGS Design Resources DSG design resources include standard specifications, drawings, sample calculations, and other technical guidelines found only in the DSG. In general, specifications define the level of quality expected, while the drawings and schedules indicate quantities, dimensions, and sizes. 9.2.4.1 Technical Specifications DSG standard technical specifications for electrical design describe SPU requirements for products and installation, quality control measures for checking the products, and for construction. These specifications are presented in Construction Specifications Institute Master SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-9 Chapter 9 Electrical Design Format 2020 or current. Electrical specifications make up only a portion of the complete specifications for a project. The DSG Specifications for Electrical Design are available in Appendix 9A - Standard Specifications for Electrical Design. 9.2.4.2 Drawings Drawings provide detailed information on quantities, size, dimensions, and relationships. Drawings and specifications form the bulk of contract documents. A cardinal rule is to avoid duplicating information in specifications and drawings to avoid discrepancies. Electrical drawings must be consistent with and reference other related drawings. For example, conduit penetrations through concrete floors must be mentioned on the structural drawings so that the conduits are put in place before a slab is poured. Civil, mechanical, I&C, and structural drawings may all need to be referenced. The need to reference other drawings from other disciplines makes electrical drawings susceptible to changes by others. It is one reason the electrical design engineer is often the last to complete project drawings. For an example set of Standard SPU electrical drawings, see Appendix 9B - Standard Drawings for Electrical Design. 9.2.4.3 Design Calculations Design calculations establish minimum guidelines and requirements for generating electrical calculations on projects. Electrical calculations should be made for all SPU projects that include electrical components and should be filed in the project notebook (see DSG section 9.4.3.3). Design calculations may be made either manually or using SPU-approved computer programs. The electrical design engineer must use only SPU-approved electrical analysis software. The results should be validated with a hand calculation or order of magnitude estimate. SPU- approved software tools include: ETAP Electrical Power Analysis Software is a basic tool for calculating short circuit, load flow, arc flash analysis, and protection and coordination. Cummins Power Suite for sizing emergency generators. CenterONE available from Rockwell Automation for laying out MCCs. Spreadsheets may also be used to perform basic electrical load calculations with programs such as Microsoft Excel. For more explanation and example design calculations, see Appendix 9C - Design Calculations for Electrical Design. 9.3 GENERAL REQUIREMENTS Electrical design engineers that work in SPU facilities must be familiar with industry standards and code requirements. If industry standards and City requirements conflict, the design engineer must discuss and document any discrepancy with the line-of-business representative, O&M manager, and owner of this DSG chapter. 9-10 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design 9.3.1 Industry Codes The principal industry codes governing the electrical components of SPU designs are the NEC and modifications to it found in the Washington state and City of Seattle codes (Table 9-1). National Fire Protection Association (NFPA) codes, such as 820 and 110, determine wastewater hazardous conditions and emergency power requirements. Appropriate codes must be verified with the project manager, architect, and local building official. Table 9-1 Electrical Codes for SPU Electrical Design Designation Code NFPA 70 NEC Washington State Electrical Code City of Seattle Electrical Code Washington State Energy Code NFPA 820 Standard for Fire Protection in Wastewater Treatment and Collection Facilities NFPA-101-HB85 Life Safety Code IFC IEEE C2 NESC Acronyms and Abbreviations IEEE: Institute of Electrical and Electronics Engineers IFC: International Fire Code NEC: National Electrical Code NESC: National Electrical Safety Code NFPA: National Fire Protection Association 9.3.2 Regulations Regulations are legal design standards that must be incorporated into design. The following regulations must be incorporated in SPU electrical design: Puget Sound Clean Air Agency U.S. Environmental Protection Agency (EPA) 9.3.3 Industry Standards Industry standards are typically opinions and recommendations that form design guidelines. They are not legal in nature but describe commonly accepted standards of practice. Standards are often published by industry associations but may also be established by SPU (Table 9-2). SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-11 Chapter 9 Electrical Design Table 9-2 Industry Standards Organizations Acronym Organization ANSI American National Standards Association NEMA National Electrical Manufacturers Association IEEE Institute of Electrical and Electronics Engineers OSHA Occupational Safety and Health Administration ASTM American Society for Testing Materials UL Underwriters Laboratory IES Illuminating Engineering Society NFPA National Fire Protection Association NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities 9.4 DESIGN PROCESS DSG Chapter 1, Design Process describes a series of steps evolved from planning through commissioning for a typical SPU project. The electrical design engineer should apply these principles to guide design decision making and evaluate possible solutions to a problem when preparing design record in the following phases: Preliminary Design. This phase identifies basic issues that could make the project electrically unfeasible due to expense or code/regulation requirements and sets the stage for the following phases. 30% Design. The Basis of Electrical Design Memorandum (see DSG section 9.4.3.2) is introduced at this phase. Lists are started and preliminary calculations are used to produce one-line drawings. 60% Design. The electrical drawings at this phase usually appear very incomplete. However, most underlying calculations, equipment selection, and layout work has been done. Detailed electrical drawings at this stage are not required. Other disciplines will usually contribute to the electrical drawings as well. 90% Design. This phase is usually completed in two parts to allow for final coordination. The 90% design should be an attempt at 100%, understanding that some relatively minor changes are often necessary to produce the final set of documents. 9.4.1 Design Checklist Checklists are used to verify that required information is included in each design phase. Table 9-3 shows approximately what is covered at the various stages of electrical design. For a detailed checklist for electrical design at SPU, see Appendix 9D - SPU Electrical Design Checklist. 9-12 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design Table 9-3 Simplified Checklist for Electrical Design Checklist Category Predesign 30% 60% 90% 100% Code Review     Deliverables      Design Coordination     Power and Light Concepts   Power Supply and Distribution     Special Systems   Basis of Electrical Design Memorandum     Calculations    Drawing List    Equipment List    One-Line Diagram     Lighting/Facility    Process/I&C x    Site Electrical x    Special Systems Riser Diagrams    Specifications    Design Fixup  Project Closeout  Acronyms and Abbreviations I&C: instrumentation and control 9.4.2 Responsibilities of Electrical Design Engineer The electrical design engineer must take an active role in consulting with other members of the project team to identify, understand, and coordinate the electrical design needs and related needs of other design team members. The electrical designer is responsible for: Supplying electrical energy to utilization equipment located on the project site. Providing adequate illumination in all areas. Providing special electrical systems such as fire alarm, security, telephone, and CCTV. Installing conduits and conductors for power distribution and for I&C systems. Selecting electric motors (e.g., enclosure type and size, horsepower [hp], and configuration). Specifying appropriate power generation. SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-13 Chapter 9 Electrical Design Selecting alternating current (AC) variable frequency and direct current (DC) drives. Determining motor controls and other electrical control circuits (in conjunction with I&C group). 9.4.3 Electrical Design Documents The electrical design engineer must produce a set of documents for each project. A typical set of documents for electrical design includes: Basis of Electrical Design memorandum Environmental conditions and materials application spreadsheet Technical specifications Drawings (electrical and instrument site plan, schedule for raceways and conductors, panels, and luminaries; diagrams for motor control and risers; one line diagram; and standard installation details) 9.4.3.1 Basis of Design Plan Sheet The basis of design plan sheet is a general sheet that shows a plan overview and lists significant design assumptions and requirements for major design elements, including electrical design. The following are SPU standards for this sheet: The design engineer must include a basis of design plan sheet in the plan set. The sheet must be archived with the record drawings. The basis of design plan sheet is not intended for construction and should not be included with the bid set. The sheet is inserted after the project has begun. See DSG Chapter 1, Design Process. For electrical design, the basis of design sheet contains the information shown in Figure 9-1. Figure 9-1 Basis of Design Plan Sheet Data for Electrical Design Electrical Design System Voltage: ________V ______Phase Available Fault Current: _____________A Total Connected Load: ______________KVA Future Capacity Required: ___________KVA Spare Requirement: ________________% Largest Motor Size: ________________hp Equipment Redundancy Load: Coincident: ______________KVA Non-Coincident: _______________KVA Hazardous (Classified) Location: Class: ____________ Division: __________ Group: ____________ Emergency Power Requirement: (choose one) □ Emergency Power System □ Legally Required Standby Power System 9-14 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design □ Optional Standby Power System Project Specific/Special Information (Assumption included): 9.4.3.2 Basis of Electrical Design Memorandum A technical memorandum is used to establish the electrical design approach and set basic electrical design criteria for a project. A Basis of Electrical Design memorandum must be prepared for each project with an electrical design component. This Basis of Electrical Design memorandum is intended to provide a reference to the original design intent, assumptions, and constraints of a project and its performance criteria for future modifications to the facility. The memo must be located and maintained electronically in the project directory (SPU’s SharePoint server), within the electrical discipline and delivery folders. Clear definition of revisions must be provided so that team members can be sure they have the latest version. For a template for the Basis of Electrical Design memorandum, see Appendix 9E - Basis of Electrical Design Memorandum. 9.4.3.3 Design Record (Project Notebook) Electrical design information should be kept in a project notebook. This notebook (along with the construction documents, specifications, and drawings) forms a complete record for the electrical portion of a project. The notebook must contain the following information: Project Information Record of Electrical Design Service: water, sewer, combined sewer overflow (CSO) Basis of Electrical Design Memorandum Type: pump station, lift station, etc. Calculations Location: address Vendor specification sheets Internal contacts (e.g., project manager) Decision log External contacts (e.g., SCL) Instructions (e.g., schedule, budget) 9.4.3.4 Coordination While the electrical design process has phases, it is highly dependent on other project disciplines. The electrical design engineer must be proactive in pursuing coordination throughout the project. Table 9-4 lists the various disciplines and types of information requiring coordination with the electrical design engineer. Table 9-4 Coordination Matrix for Electrical Design Discipline To Electrical From Electrical Mechanical Pump motors Motor types/accessories Valve actuators Voltages available Motor starting methods Architectural Facility layout Equipment space requirements SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-15 Chapter 9 Electrical Design Discipline To Electrical From Electrical Lighting characteristics Luminaries and emergency lighting Occupancy ratings Hazardous material quantities Structural Types of construction Equipment needing support Penetration/embedment restrictions Conduit routing requirements Seismic requirements Equipment needing restraint Equipment pad types Equipment needing pads Process Importance Backup power options Sequencing/redundancy Distribution configuration Design life Materials choices Future capacity Instrumentation Power requirement Recommended source Signal type Signal cable Specify Control Manual/automatic Equipment requirements Discrete, analog, network Equipment capability/limitations SCADA Transmission medium HVAC Heater loads Voltages available Ventilation loads Interlock requirements Control requirements Indicator/monitoring Odor Control Fan loads Voltages available Chemical equipment loads Control requirements Sound Noise limits Equipment sound characteristics Attenuation methods Security Communication bandwidth Conduit routing requirements Load requirement Equipment needing supports Acronyms and Abbreviations HVAC: heating, ventilation, and air conditioning SCADA: supervisory control and data acquisition 9.5 DESIGN GUIDE This section describes general components of electrical design. The assembly of conductors and electric circuit protective and control equipment is called an electrical system. Components within 9-16 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design the system include motor controls, lighting, and special systems such as telephone, security cameras and detectors, card readers and locks, pagers, and fire alarms. No single electrical system is adaptable to all SPU projects. Some SPU projects have no electrical components. When a project does require an electrical component, the specific requirements must be analyzed and the electrical system designed to meet those needs. Any approach to electrical design should include several considerations that will affect overall design. The most important consideration is safety of personnel and preservation of property, followed by reliability and continuity of service. Note: Throughout this section, the DSG specification for an electrical system component is shown in brackets, although not all components have a specification. Specifications are listed in Appendix 9A - Standard Specifications for Electrical Design. 9.5.1 Reliability and Redundancy Reliability and redundancy requirements for SPU projects are driven by the applications of facilities and determined during preliminary engineering. The design engineer must consult and determine what level of reliability is required and then evaluate alternatives to determine the most cost-effective means of supplying it. The need for increased reliability must be weighed against the increased cost of providing it. 9.5.1.1 Reliability Some SPU facilities are more critical than others. For most SPU process designs, system reliability is important (e.g., water pump stations must maintain pressure). SPU recommends that ANSI/IEEE Standard 493, IEEE Recommended Practice for Design of Reliable Industrial and Commercial Power Systems, be used to evaluate reliability requirements. At the time of DSG publication, SPU was applying RCM principles to help determine what maintenance can be done and is worth doing so that its infrastructure assets continue to operate as intended. 9.5.1.2 Redundancy One means to improve power system reliability is to increase redundancy (see Table 9-5). Redundancy can be as simple as a standby engine generator or a transfer switch for a single pump station. The electrical design engineer should use the following to determine redundancy requirements: ANSI/IEEE Standard 493, which contains examples of how redundancy increases reliability. U.S. Environmental Protection Agency’s (EPA) reliability criteria: Technical Bulletin EPA- 430-99-74-001, Design Criteria for Mechanical, Electrical, and Fluid System and Component Reliability. The design engineer must verify the level of redundancy the utility provides. In some cases, it may be sufficient to receive power from two separate lines from the same substation. In others, the ultimate source may need to be different transmission grids. This investigation should be done during preliminary engineering, when facility reliability and redundancy requirements are established. SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-17 Chapter 9 Electrical Design Table 9-5 Typical Applications of Redundancy Facility Redundancy Maintenance or Control Building A single power supply with emergency lighting units for egress lighting and an uninterruptible power supply for computer systems Water Treatment Plant A primary selective power service from the utility, with a standby generator for critical loads such as high-service pumping and disinfection Wastewater Treatment Plant Two primary services from the utility: a secondary selective low-voltage system with a standby generator for critical loads, and an uninterruptible power supply for computer-based control systems Water Booster Pump Station A single electrical service with a standby generator and transfer switch capable of supplying the entire load at the station Sewage Pump Station A single electrical service with a standby generator and transfer switch capable of supplying the entire load at the station 9.5.2 Environmental Materials and Equipment Location This section describes SPU standards for environmental materials and locations for electrical equipment. 9.5.2.1 Indoor Locations Enclosures installed indoors in dry, industrial-type areas should be NEMA 12. NEMA 1 enclosures may be used in electrical rooms, offices, and laboratory areas where flying dust and debris would not be present. NEMA 4 enclosures should be installed in indoor damp and wet areas that do not have corrosive atmospheres. Where corrosive atmospheres are also anticipated, 316 stainless steel or reinforced fiberglass NEMA 4X enclosures should be installed. 9.5.2.2 Outdoor Locations Enclosures installed outdoors and/or underground vaults must be designed to meet many conditions. If the atmospheric conditions are unknown, NEMA 4X 316 stainless steel enclosures should be installed. If it is known that no corrosive atmospheric conditions can be expected, then NEMA 3R or NEMA 4 enclosures could be used. NEMA 4 enclosures should be used in process areas where wash-down can be expected. NEMA 3R can be used for disconnect switches and similar equipment, where it is located away from process equipment. Thermal management must be considered during design for outdoor enclosures with electronics like a SCADA cabinet. The electrical design engineer should consider adding an air-conditioner and sun shield for outdoor enclosures that house uninterruptable power supplies (UPS). 9.5.2.3 Hazardous Locations A hazardous location is an area that may be subject to explosive concentrations of flammable gases or suspended combustible dust (see NFPA Fire Codes and NEC Articles 500, 501, and 502). All electrical design must follow the NEC 500 series articles. Equipment enclosures in hazardous locations should be classified. The two most common are: NEMA 7 enclosures, for use in Class I Group A, B, C, and D locations (gaseous hazards). 9-18 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design NEMA 9, for Class II Groups E, F, and G locations (explosive amounts of dust). The electrical design engineer must work with the process engineer, mechanical engineer, and architect to define hazardous areas. These areas must be clearly defined on the drawings and Project Manual. For CSO reduction storage and wastewater handling facilities, NFPA 820, Fire Protection at Wastewater Treatment and Collection Facilities, should be followed to classify hazardous areas and requirements for fire protection, fire detection, and fire-fighting requirements, such as ventilation requirements and use of explosion-proof electrical equipment and conduit sealing requirements. Table 9-6 lists other standards for classifications of hazardous areas. Note: Fire sprinkler systems are normally omitted in facility electrical rooms; hence, electrical engineer is advised to follow NFPA 13 standards and requirements for specific fire rating and protection of electrical equipment. Table 9-6 Other Standards for Classifications of Hazardous Areas Standard Content NFPA 13 Standard for The Installation of Sprinkler Systems NFPA 52 Standard for Compressed Natural Gas Vehicular Fuel Systems NFPA 58 Storage and Handling of Liquefied Petroleum Gases NFPA 70 NEC NFPA 497 Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas NFPA 499 Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas ANSI API Recommended Practice for Classification of Locations of Electrical Installations at (RP500) Petroleum Facilities ANSI C2 NESC NFPA 820 Standard for Fire Protection in Wastewater Treatment and Collection Facilities ANSI/ Standard for Safety, Intrinsically Safe Apparatus and Associated for Use in Class I, II, and UL 913 III, Division 1, Hazardous (Classified) Locations Acronyms and Abbreviations ANSI: American National Standard Institute NEC: National Electrical Code NESC: National Electrical Safety Code NFPA: National Fire Protection Association UL: Underwriters Laboratory A full discussion of hazardous location design is beyond the scope of this DSG chapter. The electrical design engineer should review the latest NEC Handbook (see DSG section 9.6). SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-19 Chapter 9 Electrical Design 9.5.2.4 Equipment Enclosures Electrical equipment enclosures must be designed for the conditions to which they will be subject when installed. ANSI/NEMA 250 defines types of enclosures and conditions for which those enclosures were designed. The most often used NEMA enclosure types are: NEMA Type 1 (indoor use only). Intended for dry indoor use primarily to provide a degree of protection against contact with the enclosed equipment. NEMA Type 3R ("weatherproof"). Intended for outdoor use primarily to provide a degree of protection against falling rain, sleet, and external ice formation. This is the least expensive outdoor enclosure. It is generally galvanized/painted steel and will quickly rust in marine air environments. NEMA Types 4 and 4X ("waterproof"). Intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water. NEMA 4X enclosures protect against corrosion. It is generally not sufficient to simply specify "NEMA 4X." NEMA does not specify a material. It is possible to certify painted steel enclosures as 4X. Premium 4X enclosures are generally stainless steel, but high-quality, non-metallic enclosures are also available. NEMA Type 12 ("dust-tight"). Intended for indoor use primarily to provide a degree of protection against dust, falling dirt, and dripping, noncorrosive liquids. Similar to NEMA 1 but has no openings and gaskets on all doors and covers. Cost slightly more than NEMA 1. For variable frequency drives (VFDs) it can be very costly. Equipment located in electrical rooms with filtered air handling systems can generally be specified as NEMA 1. 9.5.2.5 Equipment Rooms and Buildings Major electrical equipment (e.g., transformers, switchgear assemblies, switchboards, and MCCs) should be installed in dedicated rooms or buildings. Smaller equipment (such as individual motor starters and panelboards) could be installed in mechanical spaces that are continuously ventilated and dry. All equipment rated above 600V, except pad-mounted transformers and metal-enclosed outdoor switchgear assemblies, should be located in dedicated spaces accessible only to qualified persons. A. Electrical Equipment NEC Article 110 contains specific requirements for location of electrical equipment. NEC Table 110-26(A) defines the working space required in front of equipment rated 600V and less. With the exception of lighting panels, the article allows equipment pieces of equal depth to be mounted above each other as long as one piece of equipment does not impinge on the working space of another. The fronts of all equipment must be at the same distance from the wall, presenting a flat vertical plane up to 6.5 feet (ft) above the floor. NEC Table 110-34(A) defines the working space required in front of equipment rated above 600V. Note that the specified values are minimums and may not provide a comfortable working space. B. Switchboards, Motor Control Centers, and Panelboards NEC Article 408.18 contains additional requirements that pertain to the location of switchboards, MCCs, and panelboards. Specifically, NEC Article 110.26 (E) requires that a dedicated space (not necessarily a room) be provided. This space must span from the floor to 6 ft high or the structural ceiling of the space, whichever is lower, and equal the 9-20 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design width and depth of the equipment. A dropped, suspended, or similar ceiling that does not add strength to a building is not a structural ceiling. Where ceiling height exceeds 6 ft, it is still advisable to maintain clear space above equipment, if possible. No equipment foreign to the electrical equipment (piping, ducts, roof drain piping, or HVAC equipment) may be allowed in this space. Rooms containing MCCs should be ventilated, not air-conditioned, so that the ambient temperatures around both the motors and their controllers are similar. Air conditioning should be considered if ventilation will not be sufficient to keep the room temperature below 40 degrees Celsius (104 degrees Fahrenheit). C. Transformers NEC Article 450 contains several requirements for installation of the various types of transformers. It also contains specific requirements for construction of transformer vaults. The need for pads should be carefully considered under MCCs, switchboards, switchgear assemblies, unit substations, and transformers. Pads are not required in dedicated electrical rooms where the floor will be dry. Installing pads under MCCs and switchboards can often require the handle of a breaker or switch to be located higher than 6 ft, 7 inches, the maximum mounting height allowed by Article 380-8. Tips: Make sure adequately sized electrical rooms are provided early in the project before the building layout is finalized. Watch out for columns in the interior of the room that will limit usable space. Working spaces with large switchboards require two exits. Check NEC Article 110. Working spaces with large switchboards and switchgear require front and rear access. Do not assume a switchboard can be located against a wall unless it is verified with at least two vendors. In general, transformers require little maintenance and can be located outside in most climates. Switchgear should be located indoors unless there is a compelling reason to locate it outdoors. The cost of walk-in type switchgear often exceeds the cost of placing the equipment inside. Ultimately, locating switchgear and/or transformers is designer and operator preference. MCC, panelboard, and metal-clad switchgear dimensions are nearly standard across manufacturers. But low-voltage switchboard dimensions and configurations can vary dramatically. Check at least two major suppliers and size the room for the worst case. Table 9-7 is a master table for environmental conditions and materials for electrical design. Typical tables may be produced for specific types of SPU facilities and customized for each project. SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-21 Chapter 9 Electrical Design Table 9-7 Environmental Conditions and Materials Applications Master Table Small Box3 Enclosure5 Water and Wastewater Raceway1,2 Raceway1,2 (Device, Pull, Large Box Enclosure (Power (Area within project) Condition (Preferred) (Typical) Junction) (Pull, Junction) (Panelboard4) Control6) Support Concealed conduit or flush panel DRY IMC EMT Steel NEMA 1 NEMA 1 NEMA12 GALV Electrical room DRY RGS EMT Steel NEMA 1 NEMA 1 NEMA 12 GALV Motor room – no pumps or DRY RGS IMC Steel NEMA 1 NEMA 1 NEMA 12 GALV piping Motor room (drywell) – pumps DAMP RGS RGS CAST NEMA 12 NEMA 12 MENA 12 AL, SST, and/or piping GALV Wastewater HAZ1-2, WET, COR PVC-RGS RGS CAST CAST N/A NEMA 4X SST AL, SST, GALV Wet well WET PVC-RGS PVC-RGS CAST CAST N/A NEMA 4 SST Wastewater HAZ1-1, WET, COR PVC-RGS PVC-RGS CAST CAST N/A NEMA 7 SST, FRP Below-grade vault – open flow WET PVC-RGS RGS CAST CAST N/A NEMA 4 SS Wastewater HAZ1-1, WET, COR PVC-RGS PVC-RGS CAST CAST N/A NEMA 7 SS, FRP Below-grade vault – closed piping DAMP RGS RGS CAST NEMA 12 NEMA 12 NEMA 12 AL, SS, GALV Wastewater HAZ 1-2, DAMP RGS RGS CAST NEMA 12 N/A NEMA 4X SS AL, SS, GALV Interior of power/control DRY RGS IMC, RGS, AL Steel NEMA 1 NEMA 1 NEMA 12 GLAV, SS pedestal7 Chemical areas8 WET. COR PVC 80 PVC-RGS, PVC, FRP NEMA 4X FRP N/A NEMA 4X FRP FRP PVC 40 Outside WET RGS PVC-RGS CAST NEMA 3R NEMA 3R NEMA 4 AL SS, FRP or AA Embedded in concrete or block DRY, COR PVC 80 RGS, PVC 80 Concrete tite CAST N/A N/A N/A above grade Steel Embedded in concrete in earth DAMP, COR PVC 80 PVC80, PVC- CAST CAST N/A N/A N/A or fluid contact RGS Direct-buried conduits9,10 WET, COR RGS RGS, PVC 80 CAST Concrete N/A N/A N/A Transition11 Buried to exposed RGS N/A N/A N/A N/A N/A N/A Transition11 Embedded to RGS PVC-RGS N/A N/A N/A N/A N/A exposed Transition Other Note 12 Notes 1 Aluminum conduit, strut, and boxes must be separated from concrete by anti-corrosion tape or other suitable means. Recommend stainless steel strut and avoid aluminum. 2 For all S (signal) conductors, use PVC-RGS with 40 mil PVC coating 3 With PVC-RGS conduit, all fittings, device boxes, and small J-boxes must be PVC coated by the conduit manufacturer 9-22 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design 4 Includes fused disconnects and safety switches 5 Provide NEMA 4 and 4X enclosures with breather fitting. 6 Including outdoor pedestals: sometimes ventilated, but usually include internal heaters 7 Adapt materials to specific chemicals. See Table 9-8. 8 Threaded or steel compression fittings 9 For signal (S) and data highway (D) cables, use in the following order the first allowed for this area: PVC-RGS, RGS, IMC, and EMT 10 Conductors in buried conduits must have XHHW type insulation. 11 Wrap RGS with anti-corrosion tape to 3 inches on either side of transition. 12 Make transitions from one type of conduit to another only at pull points or junction boxes. Exception: from buried to exposed use at least 10 ft of PVC-RGS. Definitions DRY: conditioned space, no condensation or other source of moisture DAMP: unconditioned space, moisture due to condensation or occasional splashing WET: subject to direct water contact CORROSIVE: exposure to uncommon chemical action such as salt air, hydrogen sulfide or hypochlorite CONCEALED: in a wall cavity other than block or masonry Acronyms and Abbreviations AL: aluminum N/A: not applicable COR: corrosive N-Met: non-metallic EMT: electrical metallic tubing PVC: polyvinyl chloride # (schedule) FRP: fiberglass reinforced plastic PVC-RGS: PVC coated RGS GALV: galvanized RGS: rigid galvanize steel HAZ #: (class) # (division) SS: stainless steel IMC: intermediate metal conduit SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-23 Chapter 9 Electrical Design 9.5.2.6 Enclosures and Framing Channels A. Material Selection for Large Enclosures and Channels Selecting the material for enclosures and framing channels must balance cost and performance. For many applications, a NEMA 4X panel may not be adequate because it does not provide chemical resistance other than salt spray. Materials for enclosures and framing channels are selected based on their suitability for atmospheres found on each project. No material is most suitable in all applications, not even 316 stainless steel. Materials that should be considered include galvanized steel, painted steel, polyvinyl chloride (PVC)-coated galvanized steel, 304 stainless steel, 316 stainless steel, aluminum, fiberglass, polyesters, vinyl esters, ABS plastics, and PVC. They have the following benefits: Galvanized steel is a low-cost metal. A galvanized steel framing channel is very suitable in dry and damp locations where corrosion is not expected. For some applications, painted steel is both strong and has superior, less costly corrosion protection than that of galvanized steel. In many applications, 304 and 316 stainless steel can be used. While 304 stainless steel is a less expensive choice, it is slightly less resistant to corrosion. For hydrogen sulfide environments, 316 stainless steel is appropriate. Aluminum is a lightweight material with high corrosion resistance for a moderate cost. It is not recommended for areas with acids or alkalis. Fiberglass and fiberglass-reinforced polyester and vinyl ester materials have superior corrosion resistance to many chemicals that cause severe corrosion of metals. SPU prefers not to use fiberglass enclosures for any control panel. Table 9-8 shows chemical resistance for various materials. B. Utility Metering Enclosures Most SPU facilities require metered utility power. The exception is a few SCADA cabinets with low power demand (unmetered). SCL has specific requirements for metering depending on amperage, voltage, and service phase. Design engineer must comply with SCL construction standards when specifying a service raceway, handhole, or metering equipment. In general, a 200A or smaller, 120/240V, 1-phase or 3-phase service requires only a meter base while a service equal or larger than 225A requires a CT enclosure and separate meter socket. Large installations with a switchboard lineup may include incoming line and metering sections. The electrical design engineer should verify the current requirements for each project. Commercial meter socket with manual bypass block is required for new services. C. Panel Penetrations Except for dry areas, enclosures of all kinds should never have top-entry conduit penetrations. Penetrations should only be in the bottom or low on the sides and always include sealing locknuts or conduit hubs with gaskets. If using gaskets on conduits, conduit grounding integrity must be active. If top penetrations are unavoidable, conduits should be routed such that any moisture and condensation from the conduit 9-24 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design run is diverted away from the panel and the penetration located such that it is not directly above any electrical components inside the panel. Table 9-8 Corrosion Resistance Chemical Other Name Corrosive Agents Rcm’d Conduit Rcm’d Enclosures Primary Treatment H2S, High Moisture Aluminum PVC- 304 SST coated steel PVC 316 SST Fiberglass Fiberglass Aluminum Sulfate Alum PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Aqueous Ammonia Ammonium PVC-coated steel 304 SST hydroxide PVC 316 SST Fiberglass Fiberglass Calcium Carbonate PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Chlorine Cl2 PVC-coated steel Fiberglass PVC Fiberglass Chlorine Dioxide PVC-coated steel Fiberglass PVC Fiberglass Ferric Chloride PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Fluorosilicic Acid Fluoride H2SiF6 PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Hydrochloric Acid Muriatic acid PVC-coated steel Fiberglass PVC Fiberglass Calcium oxide Lime PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Ozone Galv Steel Aluminum Galv Steel PVC-coated steel 304 SST PVC Fiberglass 316 SST Fiberglass Polymer Galv Steel Galv Steel Aluminum 304 SST PVC-coated steel 316 SST PVC Fiberglass Fiberglass Potassium PVC-coated steel 304 SST Permanganate PVC 316 SST Fiberglass Fiberglass SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-25 Chapter 9 Electrical Design Chemical Other Name Corrosive Agents Rcm’d Conduit Rcm’d Enclosures Sodium Bisulfate PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Sodium Carbonate Soda ash PVC-coated steel Fiberglass PVC 304 SST Fiberglass 316 SST Sodium Chlorite NaCLO2 PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Sodium Hydroxide Caustic soda NaOH PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Sodium Hypochlorite PVC-coated steel Fiberglass PVC Fiberglass Sulfuric Acid PVC-coated steel 304 SST PVC 316 SST Fiberglass Fiberglass Notes 1 Conduit and enclosure type may also depend on other environmental factors such as temperature, moisture, sunlight, or sea air. The electrical design engineer must account for these factors when selecting materials. SPU prefers minimal use of aluminum materials. Acronyms and Abbreviations PVC: polyvinyl chloride SST: stainless steel 9.5.2.7 Mounting Heights Equipment and devices should be mounted at the heights listed in Table 9-9. Exceptions are equipment and other devices, which may be mounted at other heights if only noted on the drawings and compliance with NEC. Table 9-9 Mounting Heights for SCADA Equipment and Devices Equipment/Device Mounting Height1 Remarks Starters 5 ft, 6 inches Safety Switches 5 ft, 6 inches Lighting Switches 4 ft Except hatch entry Selector Switches 4 ft Outdoor Receptacles 4 ft Above grade Standard Receptacles 3 ft 4 ft wet & damp locations Clock Receptacle 1 ft, 6 inches Below ceiling 3-Phase Receptacles 4 ft, Telephone Outlets 2 ft, 9-26 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design Equipment/Device Mounting Height1 Remarks Emergency Lighting 8 ft–10 ft Interior lighting 8 ft-10 ft Notes 1 From finish floor to centerline of equipment unless otherwise noted. 9.5.3 Voltage This DSG covers nominal standard system voltages of the low and medium-voltage class. Voltage considerations for SPU projects follow ANSI/IEEE Standard 141 (ANSI C84.1) for nominal standard system voltages and their tolerances. The standard defines three voltage classes: Low voltages are used to supply utilization equipment and, by definition, are 1,000V and less. Medium voltages are used as primary distribution voltages to supply step-down transformers to low-voltage systems and are greater than 1,000V but less than 100,000V. Medium voltages of 13,800V and less are also used to supply utilization equipment such as large motors. High voltages are used to transmit large amounts of electrical power between transmission substations, and are higher than 100,000V. Note that the design of high- voltage systems is beyond the scope of this document. Table 9-10 shows system voltage nomenclature used in the United States. Table 9-10 Electrical System Voltage Nomenclature (United States) Name Description Single-number 2-wire, 1-phase system where the voltage indicated is the nominal voltage 1-phase voltage between the two wires Example: 120V, 1-phase Single-number 3-wire, 3-phase system where the voltage designates the nominal voltage 3-phase voltage between any 2-phase wires Example: 480V, 3-phase 2-voltage designation where 3-wire, 1-phase voltage in which the nominal voltage between phase smaller number is first conductors is 240V and the nominal voltage between either phase conductor and neutral is 120V Example: 120/240V, 1-phase Designation such as 480Y/277 4-wire, 3-phase system supplied by a wye connected transformer. The first or 208Y/120V, 3-phase number indicates the nominal phase-to-phase voltage and the second number indicates the nominal phase-to-neutral voltage Designations such as 240/120V Generally, a 3-phase delta system, in which one phase is center-tapped, with the center tap grounded to provide 120V power. These are often referred to as "red-leg" or “wild/Hi-leg" delta systems. Note: Wild-leg systems are typically used for small pump stations where little 120V power is required. They should be avoided for general use because 120V power is inherently limited. SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-27 Chapter 9 Electrical Design Typical voltage for SPU facilities is 480V, 3-phase. Where possible, SPU prefers 480Y/277V. SCL supplies most City electrical systems. SCL typically supplies 240/120V 1-phase to residential areas while industrial areas are equipped with 480V systems. Low-voltage power for lighting, receptacles, and miscellaneous power needs should be distributed at 208Y/120V, 3-phase, 4-wire, unless some other power need dictates a different voltage. Low-voltage power should be supplied by installation of 480Y/208V, 3-phase transformers located at each load center. Instruments should be powered from a separate supply transformer and panelboard or directly from the control panel. Many 480V systems are provided with a neutral and are rated 480Y/277V, 3-phase, 4-wire system, with the 277V line-to-neutral voltage used for lighting circuits. The use of 277V loads presents problems in ground fault protection when using double-ended substations. Small dry- type transformers rated either 480-120/240V 1-phase or 208Y/120V 3-phase are then provided to supply 120V lighting and convenience receptacles. Where several individual loads of 500 kilo- volt ampere (kVA) or more must be supplied, 4,160V or higher should be considered for this equipment. Power distribution voltage often depends on the supply voltage available from the serving utility. In a case where the load is small and located in a concentrated area, service from the utility at 480V, 3-phase should be specified. Larger sites (where loads are spread out and a number of unit substations are required) should be supplied at a higher voltage. If the distribution system is directly connected to the incoming utility feeder, the voltage is generally 12 kilovolt (kV). If there are large motors that could be supplied at a higher voltage, distribution voltage could be 4,160V to supply the large motors without additional transformation. Tips: For facilities with total load up to about 2,500kVA, SPU prefers distribution voltage should be 480V, 3-phase system. For higher loads and/or long distances, medium voltage should be evaluated. For large facilities with medium voltage distribution, keep unit substation transformer sizes at 2,500kVA or less to reduce the fault current available at 480V. Except for office buildings or other commercial facilities, avoid 480Y/277V 4-wire systems. Use 208/120V 3-phase, 4-wire systems for 120V system distribution whenever possible. Avoid 240/120V 3-phase systems except for very small pump station applications where most of the load is 240V 3-phase. These "wild/Hi leg" systems have limitations in their ability to provide 120V 1-phase power. 9.5.4 Wiring and Protection This section describes SPU standards for wiring and protection. Note: Throughout this and the following sections, the DSG specification for an electrical system component is shown in brackets. Not all components have a specification. A full list of specifications is available in Appendix 9A - Standard Specifications for Electrical Design. 9-28 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design 9.5.4.1 Protective Devices Electrical systems and equipment must be protected against overcurrent, phase-to-phase faults, and phase-to-ground faults. Two basic types of protective devices are the fuse and circuit breaker. A variety of devices fall within these two broad categories. A. Fuses [Spec 26 28 13] A fuse protects a circuit by fusing open its current-responsive element when an overcurrent or short circuit passes through it. A fuse combines both direct sensing and interrupting elements in a single, self-contained device. A fuse is also direct acting. That is, it responds to a combination of magnitude and duration of circuit current flowing through it. It is 1-phase, non-resettable and cannot interrupt a circuit during normal operation. A fuse must be used in conjunction with a switch for normal circuit interruption. Fuses are often used in combination with circuit breakers to provide current-limiting and increased fault- interrupting capacity. Advantages Disadvantages Low cost—generally the lowest cost option Nonrenewable—must be replaced after operation High interrupting capacity Operates phase-independently—risk of 1-phase operation Current limiting Must be used in conjunction with switch to interrupt normal load current Generally, requires more space than comparable circuit breaker (low voltage) Can be difficult to determine whether fuse is blown B. Medium-Voltage Circuit Breakers [Spec 26 28 16] Circuit breakers for 5-kV and 15-kV systems are similar to a molded case circuit breaker. However, medium-voltage circuit breakers are larger and more sophisticated and can interrupt much higher currents. Standard technology is the vacuum interrupter. In vacuum-type breakers, the breaker contacts are enclosed in a vacuum bottle and the arc drawn during operation is contained within this vacuum. Older medium-voltage circuit breakers use air circuit breakers in which the arc was drawn in air, then pulled into large arc chutes. Medium-voltage circuit breakers do not come with built-in overcurrent or short circuit protection. They must be specified with protective relays, typically 3-phase overcurrent relays, and one ground relay. Advantages Disadvantages Nondestructive operation—can be reused after Higher cost than fuses fault interruption Lower fault interruption capability compared with Inherently 3-phase operation fuses Combines switch and overcurrent protection in Not current limiting (except for specially designed one device breakers) Wide selection of types available Molded case breakers must have instantaneous trip (per UL); therefore, at high fault levels, coordination with standard molded case breakers is not feasible SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 9-29 Chapter 9 Electrical Design C. Low-Voltage Circuit Breakers [Spec 26 28 16] Low-voltage circuit breakers have contacts to determine that an overcurrent condition has occurred. Two major classifications of low-voltage circuit breakers are defined in ANSI C37.100: molded case circuit breaker and low-voltage power circuit breaker. For most SPU applications, some form of molded case circuit breaker is preferred. The standard molded case circuit breaker has a thermal-magnetic trip unit with two separate functions: overload protection and short-circuit protection. More sophisticated devices are available, with solid-state (static) trip units offering much greater flexibility in breaker adjustment. D. Low-Voltage Ground Fault Protection Ground fault protection should be provided on all of the following: Transformer secondary and service entrance breakers rated 1000A or more. Feeder breakers rated 800A or more that are downstream of a circuit breaker equipped with ground fault protection. Motor branch circuit breakers for motors of 100 hp and more. Ground fault protection on transformer secondary and service entrance circuit breakers and feeder breakers should have adjustable time delays. Design should consider zone selective interlocking to minimize outage to the zone nearest the ground fault. Ground fault protection provided on motor circuits should be the instantaneous tripping type. E. Selection of Protective Devices Selecting protective devices depends on cost, engineering preference, nature of facility, and quality of maintenance staff. Table 9-11 lists recommended protective devices. Table 9-11 Medium and Low-Voltage System Protective Devices System Type Protective Device Medium Voltage Systems Main Switchgear—Large Facility Medium-voltage circuit breakers (metal-clad switchgear) Main Switchgear—Small Facility Fused interrupter switches (metal-enclosed switchgear) Transformer Primary Fused interrupter switch Low Voltage Systems Panelboards Standard molded case circuit breaker (thermal-mag) Switchboards ≤ 400A Main and feeders > 100A: adjustable instantaneous molded case Feeders ≤ 100A: standard molded case Switchboards > 400A Main: molded case with solid-state trip unit Other—same as above Switchboards > 2,000A Main and feeders: insulated case with solid-state trip unit Switchboards > 2,000A—Critical Facilities Main feeders: low-voltage power circuit breaker with solid-state trip unit 9-30 SPU Design Standards and Guidelines Chapter Owner: Tim Kim February 2024 Chapter 9 Electrical Design System Type Protective Device High Fault Currents—480V Circuit breakers up to 65,000A For higher fault duties, use listed circuit breaker/fuse combination for up to 200,000 RMS Acronyms and Abbreviations A: amps RMS: root mean square V: volt 9.5.4.2 Conductors and Cables [Spec 26 05 19] Copper is used for most applicatio

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