Reading a Wiring Diagram
This is the skill of correctly interpreting the drawing that shows the electrical connections of a system. Diagrams are generally given in two forms: the schematic diagram showing function and the wiring diagram showing physical layout. A significant share of installation errors comes from confusing these two forms.
The schematic diagram describes signal flow and logic; components are placed so as to be legible on paper and their position has nothing to do with reality. The wiring diagram, on the other hand, shows which strand goes to which terminal, together with connector pin numbers.
- Legend first: do not start on the drawing before reading the symbol explanations and the abbreviations. The same symbol can mean different things at different manufacturers.
- Supply and return: trace the positive and negative paths on the diagram by marking them with a pencil; on most diagrams the return path is abbreviated to a single earth symbol and where it actually goes is stated separately.
- Pin numbers: connector pin numbering is generally given as seen from the mating face of the socket; do not count pins without confirming which face it is viewed from.
- Revision: check the date and revision number of the diagram; connecting a new device with an old drawing is a common mistake.
Reading the diagram from beginning to end before starting installation and working out the number of strands needed saves you from having to pull extra cable later.
Context in which this term is used: Installation, redundancy and field continuity