Maximum demand is the highest level of electrical power a site draws from the grid over a defined period, typically measured in kW (or kVA) and often calculated as an average over a time interval (for example, 15 minutes or 30 minutes). It represents the site’s peak load and is commonly used by utilities to size connections, assess capacity, and apply demand charges.
What Is Maximum Demand?
Maximum demand captures the peak electrical loading of a building or facility, including all simultaneous consumers such as HVAC, lighting, machinery, and EV charging. It is usually recorded by the site’s main meter or energy management system as the highest interval-based demand within a billing period.
Maximum demand is not the same as instantaneous spikes. It typically reflects sustained load over a set window, which makes it more relevant for grid impact and billing.
Why Maximum Demand Matters for EV Charging
EV charging can significantly increase peak site load, especially when multiple chargers operate at the same time. Managing maximum demand helps to:
– Avoid exceeding the site’s available connection capacity and main fuse rating
– Prevent nuisance trips at main LV panels and upstream protection
– Reduce electricity bills where tariffs include demand charges
– Enable more chargers on the same electrical connection using managed charging
– Improve reliability and uptime by keeping the site within safe operating limits
For fleets, uncontrolled simultaneous charging (shift end, depot return) is a common cause of new demand peaks.
How Maximum Demand Is Measured
Maximum demand is typically determined by:
– Utility meters that calculate average demand over fixed intervals (e.g., 15-minute demand)
– Building energy management systems (BMS) or power meters (with CTs)
– EV charging management platforms when combined with site load monitoring
The “maximum demand” value is usually the highest recorded interval demand in a month (or billing cycle).
Maximum Demand vs Connected Load
Maximum demand (real peak usage)
– Highest measured site demand over time
– Depends on behavior and simultaneity of loads
Connected load (theoretical total)
– Sum of rated powers of installed equipment
– Often much higher than what occurs in practice due to diversity
In EV charging design, both are used: connected load for worst-case planning and maximum demand for real-world optimization.
How to Reduce Maximum Demand in EV Charging Sites
– Implement dynamic load management to cap total EV load below a site limit
– Use load balancing to share available power across multiple chargers
– Apply managed charging schedules to shift charging to off-peak hours
– Set a site-level charging cap tied to main fuse rating or contracted capacity
– Prioritize critical vehicles (fleets) and delay non-urgent sessions
– Coordinate charging with onsite generation (PV) or storage where available
Common Causes of High Maximum Demand
– Multiple EVs starting charging simultaneously at full power (e.g., 22 kW AC)
– Coincidence with other peak loads (HVAC start-up, production shifts)
– Lack of site monitoring, causing hidden peaks
– Incorrect charger configuration (too high maximum charge current)
– Poor phase/load distribution in mixed single-phase and three-phase environments
Related Glossary Terms
Demand charges
Peak demand
Connection capacity
Main fuse rating
Main LV panels
Load balancing
Dynamic load management
Managed charging
Maximum charge current
Energy meter