Import capacity is the maximum electrical power (kW) a site is allowed or able to draw (“import”) from the grid at its connection point. It is defined by a combination of the utility connection agreement, physical infrastructure limits (transformer, cables, switchgear), and sometimes tariff structures. In EV charging, import capacity is a key constraint that determines how many chargers can operate simultaneously and at what power.
What Is Import Capacity?
Import capacity may be expressed as:
– A contracted maximum demand (maximum kW or kVA)
– A main breaker or fuse rating that caps current
– A transformer or service connection limit
– A capacity reservation in the distribution network
It applies at the point of common coupling (PCC) where the site connects to the grid.
Why Import Capacity Matters for EV Charging
EV chargers can add significant new load. Import capacity affects:
– Maximum number of charge points that can be active at once
– Feasibility of higher-power charging (e.g., 22 kW AC, DC fast charging)
– Risk of tripping main protection or exceeding contractual limits
– Utility upgrade requirements and connection lead times
– Operational costs where demand charges or capacity tariffs apply
For fleets and commercial sites, import capacity often becomes the limiting factor long before parking space does.
Import Capacity vs Hosting Capacity
These terms are related but different:
– Import capacity is the maximum grid draw allowed at the connection point
– Hosting capacity describes how much additional load the local grid and site can accommodate without violating technical limits (voltage, thermal, power quality)
– A site can have high hosting capacity locally but still be capped by a low contractual import capacity, or vice versa
What Determines Import Capacity
Import capacity is typically constrained by:
– Utility service connection rating and transformer size
– Feeder cable ampacity and thermal limits
– Main switchboard and protective device ratings
– Contracted supply limits and capacity tariffs
– Voltage drop and power quality constraints at higher loads
– Coincidence with other building peaks (HVAC, production, lighting)
Managing EV Charging Under Limited Import Capacity
When import capacity is limited, EV charging can still scale using:
– Dynamic load management to cap total site load
– Load balancing across chargers to share available power
– Smart schedules that shift charging to off-peak windows
– Power throttling based on real-time site demand
– Grid-connected storage (BESS) for peak shaving and capacity deferral
– PV integration to reduce net import during daytime charging (where applicable)
These strategies allow higher connected charger capacity without exceeding import limits.
Practical Implications for Project Design
Import capacity influences early design decisions:
– Whether to deploy more lower-power AC chargers vs fewer higher-power units
– Whether a new transformer or medium-voltage connection is required
– How to size switchboards, feeders, and protection coordination
– How to configure CPMS rules to protect the site and user experience
– How to plan expansion phases as fleet size or utilization grows
Related Glossary Terms
Hosting Capacity
Connection Capacity
Point of Common Coupling (PCC)
Demand Charges
Capacity Tariffs
Dynamic Load Management
Load Balancing
Power Throttling
Grid-connected Storage (BESS)
Feasibility Study