How should your business sub-meter EV charging energy?

A sub-meter measures a defined part of your site's electricity use, such as the charging circuit. It helps you allocate costs, but does not automatically create a separate supply contract. Ofgem's EV guidance distinguishes secondary measurement from the premises meter [S1]. For billing, check approval evidence under the Measuring Instruments Regulations 2016 where applicable [S2]. Checked October 2026.

Last checked 16 October 2026

Do you need a separate meter for business EV charging?

Decide what you need the measurement to do. You may want to separate charging from the building, allocate departmental costs or invoice individual users. These are different specifications. Ofgem explains that the main premises meter does not identify which devices consume the electricity; secondary measurement can identify the charging share [S1].

Start with a marked-up electrical drawing. Ask your installer to show the main supply meter, charging circuit, proposed sub-meter and individual charging outlets. Write the intended use beside each reading. That exercise helps you request the right equipment and data without assuming that a new electricity account is needed.

Read MID metering on chargers before specifying a measurement for invoicing. OPSS distinguishes type approval from complete conformity assessment for billing [S2]. For general project planning, start with the guide hub.

Can a smart meter separate your chargers from the building?

A premises smart meter can record consumption at different times. That does not identify individual devices; Ofgem explicitly makes this distinction in its EV guidance [S1]. Ask which additional measurement supports the breakdown your reporting system displays.

For procurement, request an example report containing both premises totals and charging totals over matching periods. Ask the person demonstrating it to identify each reading’s source. If a figure is estimated, keep that label in the export rather than treating it as measured consumption.

Specify whether the report is for internal monitoring or customer billing. Read the charging data guide. Keep a written record of which system your accounts team should use when different dashboards show different totals.

What is the difference between a circuit meter and session records?

Request a measurement schedule alongside the wiring drawing. It should connect each reading to the question you need answered. The table below is a suggested design brief, not a claim that every installation needs every item.

Ask for a demonstration of the proposed billing workflow using identified sample records. OPSS describes approval arrangements for meters used in billing [S4]. Software access and an approved measuring instrument should be checked as separate items, with responsibility for each stated in the quotation.

How should you reconcile charging reports with the electricity bill?

Choose matching start and end times. Keep the opening and closing meter registers, session export, excluded equipment and adjustment notes together. Ask the installer to identify which loads each meter includes before investigating a difference. This is a suggested accounting control, not a statutory tolerance.

For illustration only, suppose the charging circuit records 1,000 kilowatt-hours, or kWh, while session reports total 940 kWh. The difference is 1,000 − 940 = 60 kWh. At an assumed energy rate of £0.25 per kWh, the associated cost is 60 × £0.25 = £15. These are invented arithmetic inputs, not a normal loss rate or tariff benchmark.

Do not automatically label the difference as a faulty meter or pass it to drivers. Ask for the measurement boundaries, missing records and included equipment to be checked. OPSS’s secondary-metering guidance retains the requirement to keep metrology accurate [S3].

How can you allocate charging costs fairly between users?

Agree the allocation method before the equipment is commissioned. Ask for a sample statement showing the measured consumption, applicable tariff, adjustments and the contact for a query. For measured consumption used in trade, Ofgem points to appropriate metering requirements [S1]. Check the contractual arrangement with your solicitor and any tax treatment with your accountant.

Suggested questions for the service specification include:

• How are shared vehicles and visiting staff identified?
• Who corrects a session assigned to the wrong account?
• How are refunds shown without overwriting the original record?
• Can your accounts team export the evidence if software changes?
• Who investigates an accuracy dispute and arranges any meter work?

Use staff charging arrangements and multi-let service charges to prepare the wider brief.

Does a sub-meter give charging its own supply contract or capacity?

Do not budget on that assumption. Ask your electricity supplier whether the proposed arrangement changes its contract or settlement meter, and ask the network operator about the connection. Government guidance treats connection requirements as a separate assessment [S5]. A sub-metering proposal should make those boundaries clear.

Compare a monitoring-only option with any proposal involving a new supply. Request separate prices and written scope for hardware, installation, data services, supply work and ongoing administration. You can then see which cost buys which function, rather than comparing headline subscription prices alone.

If you are also sizing charging, distinguish kWh energy from kilowatts, or kW, of power. Explain how much energy the vehicles need and when they leave; ask the designer to turn that requirement into a connection request [S5].

What should you do next?

Prepare the measurement drawing and a sample statement you would be comfortable explaining to a user. Bring them to a site survey, then get matched with an installer that covers your area.

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