Electrical Single Line Diagram

Last Updated: November 30, 2019

Definition - What does Electrical Single Line Diagram mean?

The Single Line Diagram (SLD) is considered as an essential tool for the electrical professional. The SLD is the blueprint for electrical system analysis. It represents a three-phase power system. It is a form of the block diagram which conveys the paths for power flow between different entities of the system.

When working in both old and new buildings, electrical engineers rely on a single-single line diagram to track the electrical components to look after proper maintenance and safety practices.

Safeopedia explains Electrical Single Line Diagram

Uses of an SLD

It works differently in a balanced and unbalanced system.

  1. In a three-phase power system, each phase is considered separately as long as the load is balanced separately in each phase. There can be asymmetric faults on one or two phases. So, here the SLD is used along with notational simplification.
  2. When using the symmetrical components method, separate one-line diagrams are made for each of the positive, negative, and zero-sequence systems.

Creating and Maintaining an SLD

After the construction of a building is completed, engineers and the builder work together to eliminate hazards related to power supply. The process goes step by step.

  1. A design engineer lays out the components and devices to be installed.
  2. The engineer creates assumptions used to estimate fault-current calculations and selective coordination needs.
  3. A contractor installs an SLD, marking-up the SLD as changes are made.
  4. The original design drawings revised to reflect changes made in the field are created.

The Importance of an SLD

  1. It is the primary resource to calculate short-circuit currents, determine selective coordination and, ultimately, calculate incident energy.
  2. Serving as a map of the electrical distribution system, an SLD documents conductors, transformers, overcurrent protective devices (OCPDs) and other electrical devices and safety mechanisms to aid in many areas of design and maintenance while reducing confusion.
  3. The simpler diagram leaves more space for non-electrical to be included.
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