Electrical System Design Process

Engineers start the process of designing electrical systems by estimating the total building electrical power load. They then plan the spaces required for electrical equipment such as transformer rooms, conduit chases, and electrical closets. The amount of energy a building is permitted to consume is governed by building codes. A building energy consumption analysis determines whether the building design will meet the target electrical energy budget. If not, the engineer must modify the electrical loads and reconsider the projected system criteria. The engineer will incorporate energy conservation devices and techniques and draw up energy use guidelines to be applied when the building is occupied. These techniques depend upon the day-to-day voluntary actions of the building's occupants, which are hard to determine during the planning phase.

Once the electrical load is estimated, the engineer and the utility determine the point at which the elec trical service enters the building and the meter location. They decide on the type of service run, service voltage, and the building utility voltage. With the client, the engineer looks at how all areas of the building will be used and the type and rating of the client's equipment, including specific electric ratings and service connection requirements.

The electrical engineer gets the electrical rating of all the equipment from the HVAC, plumbing, elevator, interior design, and kitchen consultants. This communication is often made at conferences where the electrical consultant makes recommendations to the other specialists regarding the comparative costs and characteristics of equipment options.

The electrical engineer is responsible for determining the location and estimated size of all required electrical equipment spaces, including switchboard rooms, emergency equipment spaces, and electrical closets. Panel boards are normally located in closets but may be in corridor walls or other locations. The architect must reserve spaces for electrical equipment.

The electrical engineer, the architect, the interior designer, and the lighting designer design the lighting for the building. Plans may have to separate the lighting plan from the layouts for receptacles, data, and signal and control systems. Underfloor, under-carpet, over-ceiling wiring and overhead raceways are usually shown together on their own plan. The engineer then prepares a lighting fixture layout. All electrical apparatus is located on a plan, including receptacles, switches, and motors. Data processing and signal apparatus is located. Telecommunications outlets, network connections, phone outlets, speakers and microphones, TV outlets, and fire and smoke detectors are shown. Control wiring and building management system panels are also indicated.

Next, all lighting, electrical devices, and power equipment is circuited to appropriate panels. The engineer will detail the number of circuits needed to carry the electrical load, and the types and sizes of electrical cables and materials and electrical equipment, along with their placement throughout the building. Panel schedules are prepared that list all the circuits for each panel, including those for emergency equipment. Panel loads are computed that show how much power is circuited through each panel. The engineer prepares riser diagrams that show how wiring is run vertically, and designs the panels, switchboards, and service equipment. After computing the sizes of wiring sizes and protective equipment ratings, the engineer checks the work. The engineer then coordinates the electrical design with the other consultants and the architectural plans, and continues to make changes as needed.

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Figure 27-4 Electrical power plan.

Interior designers are also responsible for showing electrical system information on their drawings (Fig. 27-4). The electrical engineer uses the interior design drawings to help design the electrical system. The interior design drawings often indicate all electrical outlets, switches, and lighting fixtures and their type. Large equipment and appliances should be indicated, along with their electrical requirements. Communication system equipment, like public phones, phone outlets, and related equipment, and computer outlets are shown. In new buildings, the location and size of equipment rooms, including switching rooms and electrical closets, should be coordinated with the electrical engineer.

The designer should be familiar with the location and size of the electrical panels, and with the building systems that affect the type of wiring used, such as plenum mechanical systems. The interior designer must know the locations of existing or planned receptacles, switches, dedicated outlets, and ground fault circuit interrupters (GFCIs). Lighting fixtures, appliances, equipment, and emergency electrical systems affect the interior design. You may need to coordinate the location of equipment rooms. The presence of an uninterrupted power supply or standby power supply is also important to know about.

The interior designer does not usually need to be completely familiar with the electrical code requirements, but there are several areas that may affect interior design work. Building codes set limits on the total amount of energy used by the building, including equipment and lighting, so the interior designer should be aware of energy-efficient options. The National Electrical Code (NEC) is also known as NFPA 70. The NEC sets the minimum standard for all electrical design for construction, and is revised every three years. It is the only model electrical code published, and is the basis for electrical codes in almost all jurisdictions. Interior designers rarely use the NEC, as it is the responsibility of the electrical engineer to design the electrical system. On smaller projects, a licensed electrical contractor will know the codes. However, since you will typically specify the location of electrical outlets and fixtures, you need to know basic code requirements. The electrical code includes restrictions on the proximity of electrical components and plumbing, for example. Standards for electrical and communications systems are set by the American National Standards Institute (ANSI), the National Electrical Manufacturers Association (NEMA), and the Underwriters Laboratories (UL). In addition, the Americans with Disabilities Act (ADA) specifies mounting heights for outlets and fixtures in handicapped accessible spaces.

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