The Importance of Single Line Diagram (SLD)

Need a site single-line diagram??

Wondering how to draw a circuit diagram?

Then this article is for you!

Inside I will answer these questions about single-line diagrams and more!?

• What is a single line diagram??
• Why do you need it?
• Types of Electrical Diagram?
• Scope of Single Line Diagram?
• Importance of updating Single line diagram?
• Single line Diagram & Safety Program?
• Or maybe you’re just interested in how to read electrical blueprints…

Ready?

Let’s go!

?What is Single?Line Diagram?

The definition of a single-line diagram or SLD is an electrical diagram or drawing that represents the components of an electrical installation system represented by symbols, and describes how the components are related. Sometimes a a single line drawing or diagram of an electrical installation is also called a one-line diagram. In this article, we will briefly discuss what an electrical SLD is, types of electrical diagrams, the importance and benefits of a single line diagram. It will also discuss the importance and needed to regularly update or update electrical installation drawing documents for the purposes of reliability, operation and electrical safety.

WHY DO I NEED A SINGLE-LINE DIAGRAM?

There are two main reasons you need it:?

For everyday operations and maintenance, as well as engineering power system studies.?

?Both require that the diagram be kept up-to-date and available.?

OPERATIONS AND MAINTENANCE?

To plan your lockout/tagout procedures, you need up-to-date primary sources of information.?

“Lockout procedure

A lockout procedure shall be developed on the basis of the existing electrical equipment and system and shall use suitable documentation, including up-to-date drawings and diagrams.”

SLDs help verify electrical circuit interlocks will not result in the re-energization of the circuit being worked on.?

“Electrical circuit interlocks

Suitable documentation, including up-to-date drawings and diagrams, shall be consulted to ensure that no electrical circuit interlock operation can result in re-energizing the circuit being worked on.”

Use up-to-date diagrams in establishing an electrically safe work condition.

“Process for establishing and verifying an electrically safe work condition?

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

Having an up-to-date SLD can help avoid longer downtimes and keep everyone safe.?

POWER SYSTEM STUDIES

Having an up-to-date SLD is required to complete a power system study.?

“Power system studies and single line diagram?

Power system studies and one-line drawings are critical to the safe and reliable operation of electrical power systems. The studies and drawings shall be readily available and maintained on a consistent basis.

A main program shall include the continual upkeep and review of the following power system studies and drawings:

1. One-line diagrams;
2. Short-circuit studies;
3. Coordination study;
4. ?Arc flash incident energy study; and
5. Load flow study.”

?The information on the SLD can be used for different types of power system studies for your site.?

• Short circuit study to ensure equipment can withstand a fault.
• Coordination study to ensure the right devices are tripped in time.
• Incident energy study to know the arc flash hazard levels on equipment.
• Load flow study to know the continuous current through the system.

Types of Electrical Diagrams

?In the field, personnel often refer to single-line diagrams as “electrical drawings”. Even though there are several types of diagrams or drawings in the electrical system. Each type of electrical diagram has a unique function. The types of electrical diagrams include:

• Ladder Diagram
• Wiring Diagram
• One-line Diagram

?Ladder Diagram

?Usually drawn like a ladder so it is called a ladder diagram.?Ladder diagram is a diagram that shows the function of an electric circuit using electrical symbols.?The ladder diagram does not show the actual location of the components.?The ladder diagram allows one to understand and solve problems in a circuit quickly.?Ladder diagrams can also be referred to as line diagrams, elementary diagrams, or electrical schematic diagrams.

?Wiring Diagram

?Wiring diagrams use electrical symbols like ladder diagrams but they try to show the actual location of the components.?Wiring diagrams are also referred to as connection diagrams.?The wiring diagram helps you to identify cables and components such as those found on equipment.

?One-line Diagram

?A one line diagram or single-line diagram is a simplified way of representing a three-phase power system.?Single line diagrams do not show exact electrical-circuit connections.?As the name suggests, a one-line chart uses a single line to represent all three phases.?This is the most basic type of electrical installation blueprint.?A single line diagram shows the rating and capacity of electrical equipment and circuit conductors and protection devices.

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Scopes of Single-Line Diagrams

?Single line diagram information typically includes:

• Incoming line (nominal voltage and amount – capacity and value)
• Main circuit breaker, main fuse, cut-outs (CTO), switch, and bus-tie
• Power transformer (rating, twist connection and earthing method)
• Feeder circuit breaker
• Fused switches relays (function, use, and type)
• Current/potential transformers (size, type and ratio)
• Transformer for control system
• All mains and load cables
• All substations, including integral relays and main panels and load properties at each feeder and at each substation
• Critical equipment voltages and sizes (UPS, batteries, generators, power distribution, transfer switches, computer room air conditioners)

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Benefit of One-Line Diagrams

• Helps identify when to perform troubleshooting and simplifies the troubleshooting process
• Accurate single line diagram will further ensure the safety of personnel work
• Meets compliance with applicable regulations and standards
• Ensure a safer and more reliable operation of the facility

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?The Importance of Updating Single Line Diagram

?An electrical single-line diagram is a blueprint of the electrical system. Creating a one-line diagram is the first step in preparing a critical response plan, enabling electrical personnel to fully understand the layout and design of the facility’s electrical distribution system.

Whether it’s a new or an existing facility, the single line diagram is the road map for all future testing, service and maintenance activities. An effective single line diagram will clearly show how the main components of an electrical system are connected. It shows the correct power distribution path from the incoming power source to each downstream load – including the rating and size of each electrical appliance, its circuit conductors, and protection devices.

Often decision makers feel that they do not need to update electrical installation diagrams, or do not even consider them important. Many industrial and commercial facilities operate without accurate single line diagrams. These conditions may be considered important until they encounter real problems or losses due to not updating or inaccurate electrical installation diagrams.

Updating One-Line Diagram?

Then what is the importance of updating a single line diagram so that we need to update it? From the electrical engineering and safety aspect,?electrical SLD is the main resource for calculating short-circuit currents, determining selective protection coordination and ultimately calculating incident energy – making it one of the most important safety documents available at the facility. Safe operation of facilities is primary, while SLDs often do not get the attention they need. This is ironic.

NFPA 70E 2015 ?(Article 205.2) mentions “A single line diagram, where provided for the electrical system, shall be maintained in a legible condition and shall be kept current”.

Updated one-line diagram provide brief maps of equipment, redundancy, and protection. Regular updates with every change needed, no matter how small.

These documents form the basis for the work of many other related functions. As an example:

• Safety management personnel and electrical maintenance personnel use SLD in the context of hazardous energy control programs and LOTO practices (log-out take-out)
• An accurate single-line diagram is needed at project tender for bidding to be accurate
• Regulations require it
• The latest SLD documents are needed when there are plans to expand factories or building facilities

Modifications to the electrical system can present new hazards. For example, changing a motor or transformer can create a greater fault current than before. Over current protection devices that have been set at a certain level can fail to work without warning.

One-line diagram documentation is also used for efficient maintenance scheduling, safety evaluation and more.

?Single Line Diagram and Safety Program

In electrical safety, based on the NFPA 70E on Electrical Safety Standards at Work, there are several studies, assessments and evaluations that require the need for us to update single-line diagrams so that these activities can be carried out. The studies, assessments and evaluations related to electrical safety include:

• Short-circuit study
• Protection coordination
• Arc flash study
• Log-out and Take-Out (LOTO) program
• Electrical safety studies and evaluations
• Electrical safety procedures etc