A Single Line Diagram (SLD) is a simplified electrical drawing that shows how power flows through a building or facility — from the utility supply right through to major switchboards, distribution boards, and critical loads — using single lines instead of showing every conductor.
It’s the master “map” that electricians, engineers, facility managers, and compliance auditors rely on.
Why Single Line Diagrams are critical for property & strata buildings
Safety & compliance
- Essential for electrical inspections and audits
- Required for fault finding and isolation procedures
Maintenance efficiency
- Technicians instantly understand system layout
- Faster repairs = less downtime
Upgrades & energy projects
- Needed for BMS integration
- Required for solar, EV chargers, metering upgrades, NABERS improvements
Emergency response
Fire crews and electricians can safely isolate power quickly
The SLD maps:
- Incoming utility supply
- Transformers
- Main Switchboard (MSB)
- Sub-main boards
- Distribution boards
- Protection devices (breaker ratings, fault levels)
- Essential vs non-essential loads
Why this matters:
- Identifies where BMS meters connect
- Shows where protection coordination must occur
- Allows safe isolation procedures
- Supports switchboard upgrades and capacity assessments
Without an accurate SLD, any switchboard modification becomes high risk.
NABERS, ESG reporting, and tenant billing, meters must be installed at specific hierarchy points.
The SLD defines:
- Whole building metering
- Tenant metering
- Essential services metering
- Mechanical plant metering
- Solar and EV charger integration
This ensures:
- Clean integration into BMS or cloud dashboards
- Correct load aggregation
- No double counting
- Clear energy accountability
SLD – Core Outcomes
One of the core outcomes of a comprehensive Electrical Audit is the development of an accurate and fully up-to-date Single Line Diagram (SLD).
The SLD provides a clear visual representation of how electrical power is distributed throughout the building — from the main incoming supply through switchboards, sub-mains, and critical loads. Over time, many commercial properties undergo upgrades, tenant fit-outs, and modifications that are never properly documented, leaving existing diagrams outdated or incorrect.
By verifying circuits, load capacities, protective devices, and infrastructure in real time, an Electrical Audit ensures the SLD reflects the true condition of the building’s electrical network.
This delivers major benefits including:
• More accurate and transparent quoting for future upgrades and expansions
• Reduced risk during modifications and tenant works
• Faster approvals from consultants and engineers
• Improved safety and compliance
• Clear load availability for incoming tenants
For large commercial tenants requiring high electrical demand, such as data centres, medical facilities, laboratories, or manufacturing users; the Single Line Diagram often forms a critical part of lease negotiations and technical due diligence. In many cases, landlords are required to demonstrate available capacity before agreements are finalised.
An inaccurate SLD can lead to costly redesigns, delays, disputes, or infrastructure failures.
A verified and professionally documented Single Line Diagram gives property owners, asset managers, and tenants full confidence in the building’s electrical capability, now and into the future.