International standards requirements on single line diagram or SLD

There is some specific requirements on single line diagram or SLD in NFPA 70E standard. An up to date SLD must me maintained and readily accessible to employee or worker.

In simple word Single Line Diagram is the complete flow of electrical circuit with information like components(protection, switching, interlocks etc) with clear data (cable size, connected load etc). Now the question is whether to maintain a single diagram is mandatory in an Industrial sites. And if so is there any criteria on which SLD would be maintained.

Some facts of maintaining a Single Line Diagram

In case of an existing single line diagram three question can be asked as such below-

  1. Is the Single line diagram up to date?
  2. Is the single line diagram is authorized by a proper body or person?
  3. Is the Single Line Diagram available to the related employee for maintenance, operation or servicing?

You see these three questions are important because a misleading single line diagram is critically

dangerous and if it is not composed by a competent person or organization, it would not be that much reliable. Lastly if the SLD is not available on site, there is no use of it at all.

International Standards about Single Line Diagram

There is some direct requirements of maintaining updated or as built Single line diagram authorized by a competent body and available on site to employee.

The NFPA 70E(Standard for Electrical Safety in the Workplace, 2004 Edition) has cover this all requirements relating to single line diagram.

01In NFPA 70E [Definition of Single Line Diagram]

Electrical Single-Line Diagram. A diagram that shows, by means of single lines and graphic symbols, the course of an electric circuit or system of circuits and the component devices or parts used in the circuit or system.

02In NFPA 70E 120.1 (2) [For Up To Date SLD]

Determine all possible sources of electrical supply to the specific equipment. Check applicable up-to-date drawings, diagrams, and identification tags.

03 NFPA 70E 120.2 B (3)Plan– [Planning for maintenance, re innovation or servicing]

(3) Plan. A plan shall be developed on the basis of the existing electrical equipment and system and shall utilize up-to-date diagrammatic drawing representation(s).

04 In NFPA 70E 120.2(E) (5) for Interlock

Electrical Circuit Interlocks. Up-to-date diagrammatic drawings shall be consulted to ensure that no electrical circuit interlock operation can result in reenergizing the circuit being worked on.


05 In NFPA 70E 205.2

A single line diagram, where provided, for the electrical system shall be maintained.

06 In NFPA 70E 340.7 (A.6) Up to date SLD to employee

Provision of complete and accurate circuit diagrams and other published information to the employee prior to the employee starting work. The circuit diagrams should be marked to indicate the hazardous components.
Electrical panels require as built single line diagram
Electrical panels require as built single line diagram for safe and efficient planning for servicing & maintenance

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