Energy sub-metering is the installation of additional electricity meters downstream of the main utility meter — on each tenant, floor, department, production line or large machine — so that consumption can be measured and allocated separately. The sub-meters are read automatically, usually over Modbus, into a central system that produces tenant recovery figures, cost allocations and consumption reports, and flags abnormal usage.
Why sub-meter?
- Tenant recovery — landlords recover electricity costs from tenants on measured, not estimated, consumption.
- Cost allocation — manufacturers and campuses assign energy cost to the department, line or product that used it.
- Finding waste — after-hours loads, equipment left running and faulty systems become visible.
- Verifying projects — solar, LED retrofits and HVAC upgrades can be measured before and after.
How the meters are installed
Sub-meters are installed in distribution boards on the circuits to be measured. Smaller loads use direct-connected meters, where the supply passes through the meter. Larger loads use CT-operated meters, where current transformers clipped around the conductors let the meter measure high currents safely. Installation must be done by a qualified electrician, and CT ratios and orientation must be recorded and checked — a reversed CT is one of the most common causes of wrong readings.
How the meters are read
Modern sub-meters provide a Modbus RTU (RS-485) or Modbus TCP interface, or a pulse output for older designs. A gateway reads all meters in the building at regular intervals, stores interval consumption and sends it to a central platform. This replaces monthly manual readings, which are slow, error-prone and give no insight into when energy was used. See how to connect a Modbus meter to the cloud.
From readings to recoveries
- Collect interval readings (commonly 30-minute) for every meter.
- Validate: fill or flag gaps, detect counter resets and meter swaps, compare the sum of sub-meters with the main meter.
- Apply the tariff structure — including time-of-use rates and demand where relevant — and allocate common-area consumption according to the lease.
- Produce tenant statements and management reports, and export to the billing or property system.
What to check before you start
- Which questions you need answered — this determines where meters go.
- Existing meters: many have communication ports that were never connected.
- Meter accuracy class and suitability for billing, and whether the lease or local regulations set requirements.
- Communications routes between distribution boards and the gateway.
- Who will receive and act on the reports.
See our energy monitoring service and property & facilities work.