Schematic diagrams are broken down according to their functional aspect with the physical location. The mechanical relationships of the component parts of the equipment are usually disregarded. Depending on the extent of the circuitry, several functional units may be shown on the same sheet or a single functional unit may be shown on one or more sheets.
Equipment markings on diagrams are composed as designation blocks.
1 Plant identification
2 location of item
3A -type of Item
3B – number of item
3 C-function of item
4 terminals and conductor markings.
The identification blocks 1 (Plant) and 2 (Location) are always entered In the diagram’s block, for example, plant is identified as = GA02, location is identified as +27in.
The alphanumeric representation of a code generally reflects the method used for filing and locating the diagrams.
When locating an item using ship diagram sheets, where a relay coil and contacts are shown through different sheets, reference codes this diagram are used.