Preparing A One-Line Diagram

The following items, if given special attention during preparation, will help to ensure complete, accurate and easily interpreted one-line diagrams:

1. Maintain Relative Geographic Relations. As far as practical, indicate approximate relative positions of components in the building or plant. This keeps the drawing intuitive because things are properly located in relation to each other.
2. Avoid Duplication. A one-line diagram is a form of shorthand. For this reason, every line, symbol, figure, and letter has a definite meaning. Therefore, the duplication of names should be carefully avoided.
3. Use Standard Symbols. Use standard symbols for the more common components.
4. Show All Known Facts. No detail within the scope of the diagram should be considered as unimportant, and the rule - when in doubt, show it - should be followed. The following checklist may help avoid the omission of important details:

   A.	Manufacturers' type designations and apparatus ratings.
   B.	Ratios of current and potential transformers, taps to be used on multi-ratio transformers, and connection of dual-ratio current transformers.
   C.	Connections of power transformer windings.
   D.	Circuit breaker ratings in volts and amperes, interrupting ratings, and type and number of trip coils on circuit breakers.
   E.	Switch and fuse ratings in volts and amperes.
   F.	Any special features of fuses (current limiting, dual element, etc.)
   G.	Functions of relays.
   H.	Ratings of machines and power transformers.
   I.	Size and type of conductors.
   J.	Voltage, phase, and frequency of incoming circuits. Indicate wye and delta systems; show whether grounded or ungrounded.

5. Show Future Plans. Future plans should be set forth in the diagram, either diagrammatically or by explanatory notes.
6. Include Correct Title Data. Care should be exercised in the assignment of titles to assure that they identify the installation accurately, without any confusion with any other part of the system.

One final warning: Describe what is known as factual, but assume nothing based upon word of mouth or guesswork. People looking at and using the one-line diagram are likely to mistake guesses for knowledge, often with disastrous results.