Electrical system design is the design of electrical

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 systems. This can be as simple as a flashlight cell

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

 connected through two wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

s to a light bulb or as involved as the space shuttle

Space Shuttle

The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

. Electrical systems are groups of electrical components connected together to carry out some operation. Often the systems are combined with other systems. They might be subsystems of larger systems and have subsystems of their own. For example a subway rapid transit

Rapid transit

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 electrical system is composed of the wayside electrical power supply, wayside control system, and the electrical systems of each transit car. Each transit car’s electrical system is a subsystem of the subway system. Inside of each transit car there are also subsystems, such as the car climate control system.

Records

Simple systems can be created by one person and require minimal records. Large systems require large teams of people and many paper and electronic records. On larger projects a company would have an electrical systems engineering

Systems engineering

Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...

 department.

With larger systems, if proper records are not kept, the construction is not neat, or care is not taken to follow appropriate standards (such as those of the National Electrical Code), the created electrical system is not likely to function as desired. To paraphrase a manager’s description of a moderate sized electrical system that his company haphazardly created, “…the wiring looked like spaghetti…it caught fire when power was applied…we settled with the customer and quit the project.”

Design

The following would be appropriate for the design of a moderate to large electrical system.

1. A specification document is written. It probably would have been written by the customer. The specification document states in plain language and numerical detail what the customer expects. If it is well written, it will be used as a reference throughout the electrical system design.
2. A functional specification
   Functional specification
   A functional specification in systems engineering and software development is the documentation that describes the requested behavior of an engineering system...
   
    (design) document that goes into more technical details may be created. It uses the specification document as its basis. Here calculations may be used or referenced to support design decisions.
3. Functional diagrams may be made. These use block diagrams indicating information and electrical power flow from component to component. They are similar to the functional flow block diagram
   Functional flow block diagram
   A Functional Flow Block Diagram is a multi-tier, time-sequenced, step-by-step flow diagram of a system’s functional flow.The FFBD notation was developed in the 1950s, and is widely used in classical systems engineering...
   
   s used with computer programs.
4. Schematic
   Schematic
   A schematic diagram represents the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the information the schematic is intended to convey, and may add unrealistic elements that aid comprehension...
   
    diagrams showing the electrical interconnections between the components are made. They may not show all the conductors and termination points. Except for one-line diagram
   One-line diagram
   In power engineering, a one-line diagram or single-line diagram is a simplified notation for representing a three-phase power system. The one-line diagram has its largest application in power flow studies. Electrical elements such as circuit breakers, transformers, capacitors, bus bars, and...
   
   s, this should show all the circuit nodes. One-line diagrams represent the three or four conductors of three-phase power circuits with one line.
5. Wiring diagram
   Wiring diagram
   A wiring diagram is a simplified conventional pictorial representation of an electrical circuit. It shows the components of the circuit as simplified shapes, and the power and signal connections between the devices. A wiring diagram usually gives more information about the relative position and...
   
   s are sometimes made. These show and name the termination points and names of each conductor. In some systems enough information can be put onto the schematics so that wiring diagrams are not needed.
6. Physically smaller systems that are built many times may use a cable harness
   Cable Harness
   A cable harness, also known as a wire harness, cable assembly, wiring assembly or wiring loom,is a string of cables and/or wires which transmit informational signals or operating currents...
   
   . A full-sized to-scale wiring diagram can be made of a cable harness. This wiring diagram can then be laid on a peg board and used to guide the construction of more cable harnesses. Harnesses can be inserted into to their equipment as an assembly. Cable harnesses that are reused many times, like automobile wiring harnesses, are created with automated machinery.
7. A wire list is made in spreadsheet
   Spreadsheet
   A spreadsheet is a computer application that simulates a paper accounting worksheet. It displays multiple cells usually in a two-dimensional matrix or grid consisting of rows and columns. Each cell contains alphanumeric text, numeric values or formulas...
   
   or list format. It shows the electrical assembly people what wires are to be connected and to where. When it is printed out on paper, it is easy for the assembly people to check off conductors as they are connected. The wire list contains at a minimum each wire name, terminal name, and wire model number or gage. It may also contain the wire termination device model numbers, voltage classes, conductor class (high-voltage, medium voltage, or control wiring), etc.