Available import capacity is the amount of electrical power a site can draw from the grid (or upstream supply) that remains unused and available for new loads, such as EV chargers. In EV charging projects, it determines how many chargers can be installed and what power levels they can operate at without upgrading the grid connection or main electrical infrastructure.
What is the available import capacity?
Available import capacity is the remaining headroom between:
– The site’s maximum permitted import limit (contracted capacity or connection rating)
and
– The site’s actual peak demand from existing building loads
It is usually expressed in kW (power) or A (current), and it can be limited by:
– Utility connection agreement (contracted kW / fuse size)
– Main switchboard and feeder ratings
– Transformer capacity (on-site or upstream)
– Phase balance constraints (single-phase vs three-phase availability)
Why Available Import Capacity Matters in EV Infrastructure
EV chargers add a significant electrical load. If a site exceeds its import limit, it can cause:
– Main breaker or fuse trips
– Voltage drops and unstable operation
– Utility penalties or forced capacity upgrades
– Reduced reliability for both the building and the charging system
Understanding available import capacity helps site owners and installers:
– Select the correct charger power level (e.g., 7.4 kW, 11 kW, 22 kW)
– Decide how many charge points can run concurrently
– Determine whether load management is required
– Avoid unnecessary grid upgrades by using dynamic load balancing
– Create scalable rollout plans with additional charger provision
How Available Import Capacity Is Determined
Available import capacity is typically assessed through a site power study:
– Review contracted capacity/utility connection limit
– Identify the main incoming protection rating and switchboard constraints
– Analyze historical load profiles from metering (peak demand, seasonal peaks)
– Calculate safe headroom (often with a margin for safety and future building growth)
– Check phase distribution and power quality constraints
– Validate assumptions with on-site measurements where needed
In practice, available capacity may differ by time of day, which is why dynamic approaches are common.
Typical Use Cases
– Office buildings adding workplace charging without increasing the grid connection
– Retail sites installing EV chargers while maintaining HVAC and refrigeration loads
– Fleet depots planning overnight charging within a limited import limit
– Residential developments allocating shared power to multiple chargers
– Public sites where grid upgrades are expensive or slow to obtain
Key Benefits of Managing Available Import Capacity
– Prevents overload trips and improves site reliability
– Reduces CAPEX by avoiding immediate connection upgrades
– Enables more chargers using smart controls and power sharing
– Improves planning accuracy for tendering and installation design
– Supports cost optimization when paired with tariffs and demand limits
Limitations to Consider
– Import capacity is not the same as available capacity on every phase
– Building load can change over time (new tenants, equipment, HVAC upgrades)
– Short-duration peaks can reduce practical headroom even if averages look safe
– Power factor and harmonics can affect effective capacity and compliance
– True headroom often requires real metering data, not only nameplate ratings
Related Glossary Terms
Grid Connection Permit
Contracted Capacity
Maximum Demand
Load Management
Dynamic Load Balancing
Active Power Throttling
Power Sharing
Site Metering
Electrical Capacity Planning
Peak Shaving