Load measurement is the process of monitoring electrical demand (current, power, and sometimes energy) at a site to understand how much capacity is being used and how much headroom remains for EV charging. In EV charging deployments, accurate load measurement is the foundation for load balancing, load management, and load curtailment, because chargers can only be controlled safely when the system knows the real-time site load.
What Is Load Measurement?
Load measurement captures key electrical values such as:
– Current (A) per phase (L1, L2, L3)
– Voltage (V) (line-to-neutral and/or line-to-line)
– Real power (kW) and apparent power (kVA)
– Power factor (PF)
– Energy (kWh) over time (for reporting and billing)
For EV charging sites, measurement can be performed at the main incomer (whole site), at distribution boards (sub-loads), or per charger circuit.
Why Load Measurement Matters in EV Charging Infrastructure
EV charging adds a significant, controllable load. Without reliable measurement, sites risk:
– Exceeding the site power limit and tripping protection devices
– Unbalanced phase loading in three-phase systems
– Poor load balancing performance (slow reaction, incorrect allocations)
– Inaccurate reporting for energy management and cost control
Accurate measurement enables smarter charging control, avoids overinvestment in electrical upgrades, and supports stable operation as charger count grows.
Where Load Measurement Is Taken
Common measurement points include:
– Main supply point (after the main breaker) to track total site load
– Transformer or switchboard feeders supplying charger groups
– Sub-meters for specific building zones or tenants
– Per-charger metering for operational analytics and billing (e.g., MID metering where required)
For dynamic control, the most important point is usually the main supply measurement, because it reflects total demand and available headroom.
How Load Measurement Is Implemented
Load measurement is typically implemented using one or more of the following:
– Current transformers (CT clamps) measuring current on each phase
– A smart meter or power meter measuring kW, kVA, PF, and energy
– Energy meters integrated into switchboards or charger cabinets
– Communication interfaces (Modbus, TCP/IP, RS-485) to feed data into an EMS or CPMS
In many installations, CTs provide fast, real-time current data, while the meter provides more complete power quality and energy information.
Load Measurement for Load Balancing
Dynamic load balancing relies on fast and accurate measurement:
– Measure total site load and compare it to the configured limit (e.g., main fuse rating or contracted demand)
– Compute available headroom for EV charging
– Send updated current or power limits to chargers (often via OCPP)
If measurement is delayed or incorrect, the system may either overload the site or curtail charging too aggressively.
Practical Considerations and Common Pitfalls
Proper installation and configuration are critical:
– CT clamps must be oriented correctly (direction matters)
– Measurements should cover all phases to avoid phase imbalance
– Sampling rate and update intervals should match site dynamics (fast-changing loads need faster updates)
– Voltage assumptions should be verified (line-to-neutral vs line-to-line)
– Meter accuracy class should match the purpose (control vs billing)
Misconfigured CT ratios, wrong phase mapping, or slow polling can lead to unstable charging, incorrect power calculations, and unexpected breaker trips.
Related Glossary Terms
Load balancing
Load management
Load curtailment
Site power limit
Current transformer (CT)
Smart metering
Phase balancing
Power factor
MID metering
Energy management system (EMS)