EV Charging Submetering for UK Businesses: MID and CT Explained
EV charging submetering means measuring the electricity your chargers use separately from the rest of your site. If you only track it for internal reporting, almost any accurate meter will do. If you use those readings to charge a tenant, employee or driver, the meter must be an appropriate, approved one. In practice that usually means a MID-approved meter, built into the charger or fitted alongside it. This guide explains what that means for UK workplaces, fleets, landlords and hosts, and how to specify metering properly the first time.
TL;DR
Submetering isolates EV charging from your main site supply, because a premises meter cannot tell a charger from any other load.
MID-approved metering is what you need when the reading decides what someone pays. Reporting-only use is a different matter.
CT metering suits larger or higher-current supplies, but the meter itself still has to be approved for billing, and the current transformers have their own accuracy class.
Onsite solar or battery storage can make a standard meter unsuitable, so tell your installer early.
Software turns raw meter data into invoices, reimbursements and cost allocation. Plan it with the hardware, not afterwards.
Table of Contents
What EV charging submetering is and why businesses use it
Your main supply meter records everything the building consumes: lighting, heating, machinery, servers and chargers together. Ofgem’s guide to selling electricity to EV drivers explains that a premises meter does not distinguish EV charging from other loads, so a secondary meter measures EV consumption separately. That meter can be built into the charger itself.
The same guide points out that smart meters measure premises-level consumption. They cannot isolate a particular device such as an EV charger. That is the gap submetering fills.
Businesses typically submeter for four reasons:
Cost allocation. A landlord, managing agent or business park operator needs to split EV electricity from the shared supply.
Billing drivers. Employees, visitors or tenants pay for the energy they use.
Reimbursement. Fleet managers repay drivers who charge company vehicles at home.
Reporting. Finance and sustainability teams want a clean figure for charging energy and cost per vehicle or per site.
The first three involve money changing hands based on a reading. That is where the rules begin to matter.
When you need a MID-approved meter
MID stands for the Measuring Instruments Directive. In Great Britain its requirements sit in the Measuring Instruments Regulations 2016. BEAMA’s guidance describes the Regulations as the domestic version of the MID, and notes that charge points used for billing need to comply.
The legal chain works like this:
Under Schedule 7 of the Electricity Act 1989, where a customer is charged by the quantity of electricity supplied, that quantity must be ascertained by a meter of approved pattern or construction, installed in an approved manner.
The government says the Measuring Instruments Regulations apply to active electrical-energy meters used for trade, including EV smart charge points whose measurements determine money charged, reimbursed or rewarded.
Ofgem’s perspective is that the key question is whether charging consumption is separately identified for a customer’s bill. If the quantity decides what is paid, the secondary meter must meet the applicable requirements.
A simple test: if a number on the meter becomes a number on an invoice, a reimbursement or a reward, specify an approved meter. If the number only appears on an internal dashboard, you have more freedom, though many businesses still choose approved meters so they can start billing later without replacing hardware.
What the display rule means
The accuracy limits in the Regulations exist so consumers are billed correctly. The government’s consultation notes that regulated meters used for trade currently need an in-built, metrologically controlled physical display, and that it proposed allowing remote displays as an alternative. Requirements like this can change, so ask your installer which approach your chosen chargers follow and confirm it against current government guidance at the time of purchase.
Transparency for the person paying
Swiss metrology guidance from METAS is not UK law, but its principles are a useful benchmark. It says measurement results should be communicated transparently, be authentic and remain non-discriminatory, meaning the reading should not be locked behind passwords or tools. The same guidance makes clear that legal metrology protects fairness of measurement. It does not guarantee service quality. For a business, the practical lesson is simple: let drivers see what they were charged for, and make the kWh figure easy to find on every receipt.
MID metering vs CT metering
People searching this topic often ask about both, as if they were alternatives. They answer different questions. MID describes whether a meter is approved for billing. CT describes how the meter senses current.
Direct (whole-current) meter | CT-operated meter | |
How it measures | Full load current passes through the meter | Current transformers produce a proportional smaller current that the meter reads and scales |
Typical use | Single chargers and smaller loads | Higher-current supplies, multi-charger boards, depots |
Billing suitability | Meter must be MID/MIR approved | Meter must be MID/MIR approved; the CTs have their own accuracy class |
Installation | Simpler, fewer parts | More components, needs correct CT ratio configuration |
The key point for billing is that MID approval applies to the meter, not to the CTs, which are specified separately for accuracy. When you request a quote for a CT-operated installation, ask for the meter approval and the CT accuracy class in writing, and confirm the CT ratio is set correctly in the meter or software. A wrong ratio gives consistently wrong readings on every invoice.
For most sites, the choice follows the electrical design:
One to a few chargers on a modest supply: chargers with built-in approved meters are usually the simplest route.
A depot or car park with many chargers on one board: a CT-operated meter on the charging distribution board may suit, with each charger metering itself where per-driver billing is needed.
Mixed estates: the best design is often both, a board-level meter for cost allocation and charger-level meters for billing.
Built-in or external metering
The Department for Energy Security and Net Zero’s smart charging review reports that charge points may use external sensors or built-in monitoring systems to measure and monitor energy consumption. So metering can sit inside the charger or be installed separately.
Built-in metering keeps wiring simple, lowers the parts count and ties the reading directly to the session. It suits workplaces and destination sites where each charger bills independently.
External metering helps when you are retrofitting existing chargers, when chargers pre-date your billing plans, or when you want one meter to cover a group of chargers. It adds a component to maintain and commission.
When you are replacing outdated chargers or migrating existing ones onto a management platform, check what metering the current units have before assuming they can bill. Many were installed for convenience rather than billing.
Billing tenants, employees and fleet users
Tenants and business park occupiers
Splitting an EV bill is not like splitting a service charge by floor area. Industry commentary has noted that apportionment is not possible in the same way as a conventional service charge, which is why measured use is the fair basis. Metering each charger, or the charging board, gives you a defensible record for managing agents and occupiers. If you recharge tenants for energy, use an approved meter and keep the readings.
Employees and visitors
If you charge drivers by the kWh, the rules above apply. Many workplaces choose a simple per-kWh price with payment through an app, card or RFID, and our guide to EV charging payment options for UK businesses covers how those compare. If you are weighing whether to charge at all, our article on how to monetise workplace charging walks through grants and fees.
Fleet drivers charging at home
Ofgem’s Optimise Prime report describes the burden clearly: when employees charge company vehicles at home, the fleet manager has to submeter the charger and calculate reimbursement using the driver’s domestic tariff, which creates administrative overhead. A charger with metering and reporting built in removes most of that manual work. For fleets weighing different ways of paying for vehicle energy, this overview of the role of fuel cards for drivers and fleet managers is a helpful companion.
For depot charging, metering is mainly a cost-control and reporting tool. Our guide to UK fleet charging costs shows how energy, hardware and grants fit together, and our piece on van fleet charging explains why starting at the depot limits grid upgrade costs.
Agreeing to dispense with certification
Government guidance says certification is not applicable to non-domestic premises or to secondary meters if the supplier and consumer agree in writing to dispense with it, but approval is still required. Treat that as a narrow paperwork point, not a way round approved meters.
Data, accuracy and software
Metering only helps if the data ends up somewhere useful. For a site with several chargers, plan for:
Session-level data: start and end time, kWh, user ID or RFID tag, charger ID.
Tariff handling: different prices for staff, visitors, fleet vehicles and peak hours.
Exports: clean files your finance team can reconcile against supplier invoices.
Alerts: meters or chargers that stop reporting should flag themselves.
There is also a regulatory baseline for smart charge points. Guidance on the Electric Vehicles (Smart Charge Points) Regulations 2021 says private charge points must measure or calculate imported or exported electricity and give owners a way to view that data, accurate to within 10%. That is a smart-charging requirement and is looser than billing-grade accuracy. A charger that meets it is not automatically fit to bill drivers.
On accuracy checking, an independent technical review by the National Physical Laboratory in 2026 confirmed a measurement system suitable for assessing chargepoint accuracy against the MID Class A threshold of plus or minus 2%, according to Transport & Energy. It shows that independent accuracy testing is becoming part of the conversation, and it is worth asking your supplier how their metering is verified.
Good monitoring also catches metering faults early. Our guide to EV charger monitoring requirements lists what to include in a tender, and our article on charging management across multiple fleet sites covers consistent reporting across locations.
Onsite solar, batteries and meter suitability
If your site has solar PV or battery storage, metering needs extra thought. Government guidance states that OPSS does not consider meters affected by onsite generation to be appropriate, and that suppliers who fail to change a meter they know to be inappropriate are not meeting their obligations under the Electricity Act 1989. Separately, the Act allows a supplier to require a meter to be replaced where replacement is needed to secure compliance or is otherwise reasonable.
The practical message: if you plan solar alongside charging, decide the metering layout before installation. Where chargers will draw from both grid and generation, the meter position and type need to match how you intend to bill. Our energy solutions for businesses team can assess solar PV and battery storage alongside the charging design so the metering is right from day one.
A pre-installation metering checklist
Use this list when you brief an installer or compare quotes.
State your billing intent. Say whether readings will determine charges, reimbursements or only reports.
Ask for meter approval details. Request the MID or MIR approval for each meter in writing.
For CT-operated meters, ask for the CT accuracy class and ratio. These should appear in the commissioning record.
Confirm how the reading is displayed. Check the display approach against current government guidance.
Tell the installer about generation and storage. Include any planned solar PV or batteries.
Check the software. Confirm it records kWh per session, supports your tariffs and exports data in a format your finance team can use.
Plan maintenance. Meters, CTs, firmware and communications all need checking over the life of the site.
Keep records. Store commissioning certificates and calibration or approval documents with your asset register.
On maintenance, a service agreement that covers metering communication faults and firmware keeps billing data reliable. Our EV charger maintenance plans are designed to cover that ongoing support.
We see metering problems most often when a site was built for charging and billing was an afterthought. The chargers work, but the readings cannot support the invoices the business now wants to send. Our approach is to ask one question at the feasibility stage: who will pay for this electricity, and how will they see what they paid? The answer decides whether you need approved meters at each charger, a CT-operated meter on the board, or both. It also shapes the software, the tariff structure and the maintenance plan. We design metering together with load management and, where relevant, solar PV and battery storage, so that the data you collect reflects how the site really runs. That keeps reimbursement, tenant recharging and public charging revenue accurate, and it avoids replacing hardware later. Our aim is to make commercial charging straightforward and commercially viable. Metering that holds up to scrutiny is a large part of that. Swift Charging
Our view: design metering around the invoice
Get metering right from the survey stage
We design, supply, install and manage commercial EV charging for workplaces, fleets, landlords, hotels, schools and public sites across the UK. That includes charger-level metering, charging software with payment and RFID, load management and ongoing maintenance, and help with available OZEV grants where you are eligible.
If you are planning a new installation or want to bring existing chargers onto a platform that can bill properly, start with our workplace EV charging solutions or arrange a commercial EV feasibility review.
For fleet depots, see our fleet EV charging solutions. For installation budgets, our guide to EV charger installation costs is a good starting point.
FAQ
Do I need a MID meter to bill staff for charging?
If you charge by the quantity of electricity supplied, the law requires an appropriate approved meter, and in practice that means MID/MIR-compliant metering. If you offer free charging and only track usage internally, the billing rules are not triggered. Many employers still choose approved meters so they can introduce charging later.
Is a CT meter allowed for EV charger billing?
Yes, provided the meter itself is approved for billing and the CTs are specified with a suitable accuracy class. CT-operated meters are common on larger supplies. Ask for approval and accuracy details in writing and confirm the CT ratio at commissioning.
Can a smart meter replace an EV submeter?
Not for separating EV use. Ofgem notes that smart meters measure premises-level consumption and cannot distinguish specific devices such as EVs, which is why a secondary meter is needed to isolate and bill for charging.
Does solar PV affect which meter I can use?
It can. Government guidance says OPSS does not consider meters affected by onsite generation to be appropriate. Tell your installer about any solar or battery plans before they specify the metering.
Is the charger’s built-in meter good enough?
It can be, if it is approved for billing and displays readings as required. A charger that only meets smart charge point data requirements, which allow accuracy within 10%, is not by that fact suitable for billing. Ask for the meter’s approval documents.
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