What Electrical Schematics Are
Electrical schematics are technical drawings that represent how an electrical system is connected and how it functions. They use standardized symbols to show components (breakers, relays, meters, chargers, terminals) and the relationships between them. In EV charging projects, schematics are essential for correct installation, commissioning, troubleshooting, and future expansion.
Why Electrical Schematics Matter
Electrical schematics help teams build and operate charging sites safely and efficiently:
– Ensure correct wiring and protection coordination (breakers, RCD/RCBO, SPD)
– Reduce installation errors and commissioning time
– Speed up fault-finding and maintenance (clear circuits and terminations)
– Provide evidence for inspections, permits, and handover documentation
– Support repeatable design across many sites
– Enable scalable upgrades (add bays, add DBs, increase supply capacity)
Common Types of Electrical Schematics
Different drawings serve different purposes. EV charging projects often include:
Single-Line Diagram (SLD)
– High-level overview showing power flow from supply → switchgear → distribution boards → chargers
– Shows ratings, protective devices, cable sizes (often), earthing arrangement
– Used for design approval, DNO discussions, and commissioning reference
Wiring Diagram (Connection Diagram)
– Detailed representation of actual wiring between terminals and devices
– Shows cable cores, terminal numbers, connector pinouts
– Used by installers and service engineers
Schematic Diagram (Functional Diagram)
– Shows functional logic: relays, contactors, control circuits, interlocks, emergency stop
– More about how it works than physical layout
– Used for troubleshooting and control validation
Panel Layout / GA (General Arrangement)
– Physical layout of devices inside a DB or control panel
– Shows component placement, cable routing, space and ventilation planning
Cable Schedule and Termination Schedule
– Lists all cables, origins/destinations, sizes, lengths, tags, cores
– Defines where each conductor terminates (terminal numbers, earth bar, etc.)
– Critical for larger depots and multi-DB sites
What EV Charging Schematics Typically Include
– Incoming supply details (voltage, phases, earthing system TT/TN)
– Main isolator and upstream protection
– Metering (site meter, sub-metering, MID/Eichrecht where relevant)
– DB protection devices and feeder circuits per charger
– RCD/RCBO strategy and any DC leakage considerations
– SPD placement and coordination
– Emergency stop / isolation logic (where used)
– Load management architecture (CT clamps/meters, controller, comms links)
– Network topology (Ethernet, cellular router, VPN, OCPP connectivity)
– Clear labeling and device identifiers matching on-site labels
Best Practices
– Use consistent naming and tagging (charger IDs, DB circuit numbers, cable tags)
– Keep SLD clean and readable; move details to schedules and wiring diagrams
– Include ratings (A, kA, kW/kVA), breaking capacities, and cable sizes where required
– Show earthing/bonding clearly (MET, PE conductors, electrodes if TT)
– Mark commissioning test points and isolation points
– Maintain “as-built” updates after installation changes
Common Pitfalls
– Mixing schematic logic and physical wiring into one unreadable drawing
– Missing earthing details (common cause of site confusion and safety issues)
– Inconsistent labels between drawings and real site equipment
– No cable/termination schedule → slow installs and error-prone maintenance
– Drawings not updated after late changes → future faults and expansion risk
– No depiction of load management measurement points → controls don’t behave as expected
Related Terms for Internal Linking
– Single-line diagram (SLD)
– Distribution board (DB)
– Earthing system
– Electrical commissioning
– Dynamic load management
– RCD/RCBO
– Surge protection device (SPD)