MID Class B / C refers to accuracy classes used for electricity meters under EU metering rules commonly associated with MID (Measuring Instruments Directive) compliant meters. In EV charging, these classes indicate how accurately a meter measures energy (kWh) for billing and other legally relevant purposes, with Class C generally being more accurate than Class B under the common classification used for many MID electricity meters.
What Are MID Accuracy Classes?
An MID electricity meter is assigned an accuracy class that defines the permitted measurement error under specified conditions. The class is used to:
– Demonstrate suitability for billing per kWh
– Support consumer protection and reduce disputes
– Ensure consistent measurement performance over a defined operating range
In practice, you will see meters labeled with a class (often B or C) on the meter faceplate and in the conformity documentation.
Class B vs Class C
Class B
– Commonly used for commercial and sub-metering applications
– Suitable for many EV charging billing use cases where regulations allow
– Typically lower accuracy than Class C
Class C
– Higher accuracy class than Class B
– Often preferred when higher precision is required (tight billing tolerance, audits, premium sites)
– Useful in high-throughput public charging where small percentage errors translate into higher financial impact
The exact allowed error bands depend on the meter standard and test conditions referenced in the meter’s documentation.
Why Class B / C Matters in EV Charging
Accuracy class impacts:
– Billing correctness and customer trust (kWh billed vs kWh delivered)
– Dispute rates and refund handling
– Tender and compliance requirements (some tenders specify a minimum class)
– Financial reconciliation in merchant account settlement and revenue share models
– Reporting quality for energy and carbon calculations (though carbon reporting often has larger uncertainties elsewhere)
Higher accuracy can be especially valuable for high utilization public sites and fleet depots with large monthly energy volumes.
Where You’ll See Class B / C Used
– Charger-integrated MID meters (session billing per connector)
– Dedicated feeder meters in meter cabinets (site-level EV energy tracking)
– Tenant and workplace sub-metering for cost allocation
For per-session billing, integrated MID metering per charger is often the cleanest approach, because it ties directly to a single charging session record in the CPMS.
Practical Selection Guidance
– Choose Class C when you need higher billing precision, strong auditability, or tender compliance specifying higher accuracy
– Choose Class B when cost and availability matter more and the application/tender allows it
– Validate local requirements: some markets specify not just “MID” but also accepted meter standards, sealing rules, and verification practices
– Ensure the CPMS is configured to bill from the correct meter register and that meter IDs are traceable to assets
Common Pitfalls
– Assuming “MID” automatically guarantees the same accuracy across all meters
– Using a feeder-level MID meter for per-session billing without a clear allocation method
– Poor installation (CT polarity, wiring errors) causing larger errors than the meter class itself
– Missing documentation or broken seals that can undermine legal-for-trade credibility
Related Glossary Terms
MID
MID metering
Energy meter
Meter cabinets
Fiscal metering
Charging session reporting
Tariff structure
CPO (Charge Point Operator)
Merchant accounts