A site power limit is a defined maximum amount of electrical power (measured in kW) that a site is allowed to draw (import) at any moment, or that an operator chooses to enforce to avoid exceeding contractual or technical constraints. In EV charging, a site power limit is used to ensure charging demand stays within:
– The grid connection agreement (main fuse / import capacity)
– The capacity of the site’s transformer, switchgear, or feeders
– A cost target (avoiding demand charges or peak penalties where applicable)
A site power limit is an instantaneous constraint (kW), not a total energy budget (kWh).
Why Site Power Limits Matter in EV Charging Infrastructure
Power limits are essential for scaling charging without constant electrical upgrades.
– Prevents tripping main protection (main fuse, breaker) and causing whole-site outages
– Enables more charge points to be installed on limited capacity using load management
– Reduces peak demand and can lower electricity cost exposure in some tariff structures
– Improves reliability by preventing uncontrolled simultaneous charging peaks
– Supports operational predictability for fleets, workplaces, and semi-public sites
How Site Power Limits Work
A site power limit is usually enforced by a load management or energy management system (EMS) using real-time measurement.
– Site power is measured at the point of connection or main distribution (CTs / meter)
– Available headroom is calculated: site limit minus current non-charging load
– Charging power is allocated across active chargers (dynamic load distribution)
– If site load rises, charging power is reduced or sessions are paused to stay within the limit
– Priority rules can allocate power to critical users (fleet vehicles, accessible bays, VIP tenants)
– Power is increased again when headroom returns
This can be implemented locally (on-site controller) or centrally (backend) depending on architecture and latency requirements.
Common Use Cases
– Workplaces where building HVAC and machinery create daytime peaks
– Apartment and multi-tenant sites with limited main supply
– Fleet depots that must avoid exceeding a fixed import capacity
– Retail sites where peak shopping hours align with peak building load
– Sites with on-site PV/battery systems that want to cap grid import
– Temporary sites where upgrades are not feasible
Site Power Limit vs Charger Power Limit
– Site power limit: max kW for the whole site (all chargers + other loads, if measured)
– Charger power limit: max kW per charge point (hardware or configuration limit)
– Circuit limit: max kW per feeder or distribution segment
A well-designed system uses all three to protect the grid connection, feeders, and individual chargers.
Key Benefits of Site Power Limits
– Avoids costly grid upgrades by using available capacity intelligently
– Prevents nuisance trips and improves site reliability
– Enables scalable rollouts (add chargers without increasing contracted capacity)
– Improves energy cost control through peak management
– Supports fair allocation across multiple users and tenants
Limitations to Consider
– Requires accurate real-time measurement and robust communications
– If the limit is set too low, charging speeds can become unacceptable for users
– Sudden non-charging load spikes can reduce charging power unexpectedly
– Poor priority rules can create unfair allocation or operational issues
– Some sites need redundancy or local control to keep limits enforced during connectivity loss
Related Glossary Terms
Maximum site demand limit
Load management
Dynamic load management
Load balancing
Managed charging
Peak shaving
Charging schedules
Site energy ceiling
Import capacity
Main fuse rating