Sub-metering is the measurement of electricity use at a level below the main utility meter—typically per tenant, building zone, distribution board, or EV charging circuit. In EV charging, sub-metering is used to track how much energy is delivered to specific chargers or charger groups so costs can be allocated accurately, usage can be reported, and charging can be managed against site limits.
Sub-metering can be installed at different points, such as a sub-distribution board (SDB) feeder, individual charger circuits, or inside the charger (depending on design).
Why Sub-metering Matters in EV Charging Infrastructure
EV charging introduces new, measurable electrical loads that often need separate accounting from the building’s general consumption. Sub-metering enables:
– Fair cost allocation in multi-tenant charging (tenants, residents, departments)
– Accurate billing for workplace, fleet, or shared parking scenarios
– Energy reporting for ESG, sustainability, and cost control
– Detection of abnormal consumption, faults, or idle losses
– Validation of load management strategies and site demand behavior
For property managers, sub-metering helps avoid disputes and supports transparent charging policies.
Common Sub-metering Use Cases
Sub-metering is widely used in:
– Apartment buildings where residents pay for their own charging
– Workplaces with cost allocation by department or cost center
– Fleet depots tracking energy by vehicle group or operational unit
– Mixed-use sites where chargers serve different user groups
– Public-private sites where some sessions are free or sponsored and others paid
Where Sub-meters Are Installed
Typical sub-metering locations include:
– At the feeder supplying a charger cluster (group metering)
– In an SDB on each outgoing charger circuit (per-circuit metering)
– In the charger itself (internal metering for session reporting)
– At a dedicated metering cabinet used for billing-grade measurement
The best choice depends on billing needs, accuracy requirements, and how granular allocation must be.
Sub-metering vs Billing-grade Metering
Not all sub-meters are suitable for invoicing:
– Sub-metering can be used for internal allocation and reporting even if it is not certified
– For public paid charging, many markets require certified metering (often MID metering in the EU) and compliant customer information
– Billing-grade metering usually involves specific accuracy classes, sealing, and auditability
Sub-metering can still be valuable even when billing-grade metering is handled elsewhere, because it supports operational visibility and energy management.
How Sub-metering Supports Load Management
Sub-metering provides the data needed to control and optimize site power:
– Identify peak usage patterns and charger diversity
– Verify compliance with a maximum site demand limit
– Detect phase imbalance and unusual load profiles
– Improve planning for expansions and spare capacity requirements
When integrated with a charging backend (often via OCPP), sub-meter data can also support automated reporting and alarms.
Benefits of Sub-metering
– Transparent cost allocation and fewer disputes
– Better energy reporting and ESG tracking
– Improved operational control and fault detection
– Data for ROI analysis, utilization planning, and capacity upgrades
– Supports scalable deployment in multi-user environments
Common Pitfalls
– Installing meters without a clear allocation model (who pays what)
– Mismatch between meter data and backend session data due to time sync or configuration
– Choosing non-certified meters when regulations require certified billing measurement
– Poor commissioning or wiring mistakes leading to incorrect readings
– Lack of documentation for which meter maps to which charger or circuit
Related Glossary Terms
MID Metering
Per-kWh Billing
Multi-tenant Charging
Sub-distribution Board (SDB)
Load Management
Load Balancing
Maximum Site Demand Limit
OCPP