Load shedding is the controlled reduction or disconnection of electrical loads to prevent an overload or stabilize the power system when available capacity is insufficient. In EV charging, load shedding means temporarily reducing charging power or switching off selected chargers (or charging sessions) to keep a site within its site power limit, avoid tripping protection devices, or comply with grid operator constraints.
What Is Load Shedding?
Load shedding is a protective measure used when demand exceeds supply or a safe operating threshold. In EV charging environments, it can involve:
– Reducing current limits across chargers (soft shedding)
– Pausing or stopping lower-priority charging sessions (hard shedding)
– Turning off entire charger groups fed by a constrained distribution board
– Enforcing emergency caps based on utility or building management signals
Unlike routine load balancing, load shedding is often triggered by urgent or exceptional conditions and aims to protect the site from failure.
Why Load Shedding Matters in EV Charging Infrastructure
EV charging can add large, simultaneous loads—especially at fleets, workplaces, and public hubs. Load shedding helps:
– Prevent main breaker trips and avoid total site downtime
– Protect cables, switchgear, and transformers from overheating
– Maintain power for critical building loads (safety systems, refrigeration, production)
– Comply with grid constraints during congestion or emergency events
– Enable higher charger density by managing worst-case scenarios without overbuilding
For many sites, the ability to shed EV load is a practical way to keep the building stable under peak conditions.
How Load Shedding Works
Load shedding is typically implemented through a control layer such as a BMS/EMS or CPMS, using:
– Load measurement (meters or CT clamps) to detect overload risk
– A defined threshold (e.g., “shed EV load if total site current exceeds 250 A”)
– Shedding rules (priority, fairness, minimum current, reconnection logic)
– Charger control commands (often via OCPP) to reduce power or stop sessions
Typical sequence:
– Detect overload condition or receive a curtailment request
– Determine required reduction and which chargers to affect
– Reduce current limits or pause selected sessions
– Restore charging gradually when capacity returns to avoid a rebound peak
Common Triggers for Load Shedding
Load shedding in EV charging can be triggered by:
– Sudden building load spikes (HVAC start, machinery, kitchens)
– Approaching main fuse or transformer thermal limits
– Utility grid events (demand response activation, congestion, emergency)
– Backup power operation (generator capacity limits)
– Fault conditions requiring temporary isolation of a feeder or distribution board
Load Shedding Strategies for EV Charging
Sites choose shedding strategies based on fairness and operational priority:
– Priority-based shedding: keep fleet-critical or reserved chargers active first
– Round-robin shedding: rotate which sessions are paused to share impact
– Minimum-service shedding: reduce all sessions to a minimum current before stopping any
– Zonal shedding: shed whole charger groups tied to a specific panel
– Time-window shedding: restrict charging during high-risk periods only
A good strategy minimizes user disruption while protecting site integrity.
Benefits of Load Shedding
– Prevents catastrophic overloads and improves site reliability
– Protects electrical infrastructure and reduces fault events
– Keeps critical building loads running during constrained conditions
– Supports grid stability and participation in demand response programs
– Enables safe operation under abnormal peak demand scenarios
Limitations and User Experience Considerations
Load shedding can affect drivers and operations:
– Sessions may slow significantly or stop unexpectedly
– Restart behavior varies by vehicle; some EVs require user re-authentication
– Frequent shedding can reduce confidence in site charging reliability
– Clear backend messaging (apps, screens, alerts) improves user understanding
Load shedding should be a last-resort safeguard, supported by proper sizing, load balancing, and realistic capacity planning.
Related Glossary Terms
Load curtailment
Load balancing
Load management
Site power limit
Demand response
Peak shaving
Energy management system (EMS)
Charge Point Management System (CPMS)
Power throttling
Load measurement