What is a SLD?
A single-line diagram (SLD) is a simplified schematic representation of an electrical power system, using a single line to represent three phases. It depicts the major components and connections in a power system, such as generators, transformers, batteries, solar inverters, power cabinets, energy meters and protective devices.
SLDs are used for system design, installation work, troubleshooting and future improvements.
Why SLDs are critical for energy management:
- Ensures accurate meter installation and configuration
- Serves as the technical blueprint for energy management hierarchy: ensures proper electrical distribution and monitoring throughout the static load balancing or dynamic load balancing on locations.
- Prevents costly delays and rework during installation
- Enables effective troubleshooting and future system improvements
- Guarantees proper electrical distribution and safety compliance
We ask our partners to deliver the SLD to Maxem. Our Technical Delivery Managers (TDMs) check and discuss the SLD in depth with the partner if needed.
Incomplete or inaccurate SLDs will result in project delays and may require site revisits.
SLD Requirements Checklist:
Modbus Meter Specifications
- Overview of all Modbus RTU and TCP meters installed
- Exact installation location for each meter
- Manufacturer name for each meter (e.g., ABB)
- Specific meter type/model for each meter (e.g., B24 212-100)
- Communication type specified per meter (Modbus RTU or TCP)
- Modbus address assigned per meter (e.g., 100 for grid connection)
Communication Parameters
- BAUD rate specified for all Modbus RTU and TCP meters (e.g., 19200)
- PARITY setting specified for all meters (e.g., EVEN)
General Requirements
- All components of energy system (solar panels, batteries, charging stations, etc) are clearly labeled and identifiable
- Electrical connections properly represented
- Communication lines clearly distinguished from power lines
- Protective devices and their ratings shown
- Current limits in amps (A) for each meter cabinet section
- Contracted power value for grid connection energy contract (kW)
- Position of Maxem energy controller clearly marked
System Hierarchy Requirements
SLD must show the complete electrical hierarchy from grid connection to end devices:
- Main Grid Connection: Include contracted capacity and main protection
- Distribution Levels: Show all distribution boards and sub-panels (subdividers)
- Load Groups: Identify different load categories (charging stations, building loads, etc.)
- Individual Circuits: Show final circuits to charging points and other loads
Process Integration
The SLD is a critical deliverable that bridges the gap between project planning and physical installation, ensuring all stakeholders have the precise technical specifications needed for successful energy controller deployment.
Most symbols that are used in SLD come from IEC 60617 (The International Electrotechnical Commission (IEC) symbols).
It is an international, standardised system used to represent various devices, including pilot lights, relays, timers, and switches for usage in electrical schematic diagrams. Please find this document here: link.
Main elements on presented as example SLD are the following:
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Symbol |
Meaning |
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___________________ |
Solid Lines: Power/electrical connections |
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- - - - - - - - - - - - - - - - -
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Dashed Lines: Communication/data connections |
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Modbus Energy Meter (kWh Meter) |
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Network Switch Ethernet network device that connects multiple devices (charging stations, meters, controllers) enabling data communication. Usually unmanaged switch for simplicity. |
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Maxem Energy Controller Central control unit that manages dynamic load balancing, monitors all connected devices, and coordinates charging station operations. Communicates via Modbus and OCPP protocols. |
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Circuit Breaker or Overcurrent Protection Device. It automatically trips if current exceeds safe levels. This indicates the physical grid limit. |
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Subdivider (distribution section) It shows how energy is distributed across location, left side indicates energy that comes from main grid and right side - different groups. |
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Power transformer that transforms high voltage into medium
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These symbols represent protective switching devices in an electrical distribution panel, specifically fuses or circuit breakers with different ratings. |
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Symbol Breakdown. In the content of this SLD it represents a group K3. Behind each group is switch that controls power for charging stations, solar panels, buildings and ect. |
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This text indicates Load Unit 1 (Dutch: "Laadpunt 1"), which represents an EV Charging Station identifier. |
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This text simply describes a kWh meter (kilowatt-hour meter), which is an energy meter. |
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Solar PV Installation with Inverter |
It is important to regularly update electrical installation drawing documents for the purposes of reliability, operation and electrical safety.
For technical questions regarding SLD requirements:
- Contact your assigned Technical Delivery Manager
- Include project location for reference in all communications
- Provide specific questions rather than general requests for help
- Document any deviations from approved SLD for review
Frequently Asked Questions
Q: Can I use symbols other than IEC 60617 standards?
A: Yes, but include a legend explaining all non-standard symbols used.
Q: How detailed should the SLD be for small installations?
A: All required elements must be included regardless of installation size (meters, subdividers, charging stations, batteries, solar panels, grid lines and communication lines).
Q: What if the actual installation differs slightly from the SLD?
A: Contact your Technical Delivery Manager. Even minor deviations may affect system operation and must be approved.
Q: Can I submit hand-drawn SLDs?
A: While not prohibited, computer-generated diagrams are strongly preferred for clarity and professional presentation.