Sub-metering

Sub-metering measures electricity, water, gas and thermal energy below the utility meter: by tenancy, apartment, floor, plant item or end use. It serves two different purposes with different requirements. Billing meters charge tenants or residents for what they use and must meet legal metrology rules; monitoring meters show where energy and water go, support ratings and catch faults, and need accuracy and reliable data but not legal approval. Many buildings have meters installed for one purpose being used for the other.

Metering also underpins compliance: ratings, disclosure and building performance standards rely on accurate whole-building and end-use data, and metering errors can misstate a building's performance to buyers, tenants and regulators.

What shortens life, or usefulness:

• Fit-outs that move circuits without updating which meter measures what.
• Communications that fail silently, leaving data gaps.
• Vendor platforms that close or change.
• Network changes, such as retirement of older mobile networks used by meter modems.

Meter hardware usually outlasts the communications and software around it, which is where most metering systems fail first.

Current transformer and wiring errors

Electricity sub-meters that use current transformers are commonly installed with the wrong ratio programmed, transformers on the wrong phase or circuit, or polarity reversed. The meter then reads a fraction, a multiple or the wrong load entirely, sometimes for years.

Mapping drift

After fit-outs and alterations, circuits are moved between boards and meters no longer measure the areas their labels say. Tenants are billed for each other's use, and plant energy is attributed to the wrong place.

Data gaps

Meters keep counting but communications fail, batteries die, or gateways lose connection; monitoring dashboards show gaps or flat lines that nobody notices.

Legal metrology non-compliance

Meters used to bill tenants or residents generally need approved patterns and verification under national measurement law. Monitoring-grade meters used for billing expose owners to disputes and regulatory action.

Accuracy decline

Mechanical water meters under-read as they wear; thermal meters drift as temperature sensors age and flow meters foul.

Embedded network obligations

Owners who on-sell electricity or gas through embedded networks take on regulatory obligations for metering, billing, hardship and customer protections. These are tightening in several Australian states.

Missing meters

Loads added after the metering design (new plant, EV chargers, tenant equipment on common supply) are often not metered at all, so the main meter and sub-meters never reconcile and costs are absorbed by the owner or spread unfairly.

On site

• Meters without clear labels of what they measure.
• Meters showing zero or impossible readings.
• Dead displays on battery-powered meters.
• Boards altered since metering was installed.

In the data

• Sub-meter totals that do not add up to the main meter.
• Flat lines or gaps in data.
• Tenancy consumption that does not match occupancy or hours.
• Negative readings on current transformer meters.

In the records

• Metering schedule and single-line diagrams.
• Meter pattern approvals and verification certificates for billing meters.
• Recharge and billing records, and tenant disputes.
• Embedded network registrations and exemptions.

• Tenants or residents questioning their bills, often the first sign of mapping or ratio errors.
• Ratings that change sharply without a physical change to the building.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

Metering findings are rarely about physical safety; their weight comes from money and compliance, because errors in billing meters affect every tenant's charges and errors in monitoring meters undermine ratings and performance standard reporting.

An electrical engineer or metering specialist, with legal advice where billing or embedded networks are involved.

• Metering audit: inventory of every meter with type, approval, location, what it measures and how it communicates.
• Reconciliation of sub-meters against the main meter over a representative period.
• Spot checks of current transformer ratios, polarity and the circuits measured, by clamp measurement.
• Mapping verification against current single-line diagrams and tenancy layouts.
• Data review for gaps and failures.
• Compliance review of billing meters and embedded network obligations.

The report should give a corrected metering schedule, faults found, compliance status and a remediation plan.

Reconciliation over several weeks, comparing sub-meter totals with the main meter by hour, separates constant errors (ratios, missing meters) from intermittent ones (communications, failing meters).

• Correct installation faults: ratios, polarity and circuit allocation.
• Update mapping and labelling after fit-outs, and make this part of every fit-out sign-off.
• Replace meters that are not approved for billing, are inaccurate or are on retiring networks.
• Improve communications and set alarms for data gaps.
• Add meters where ratings or performance standards need end-use data.
• Embedded network compliance or exit, depending on obligations and economics.

• Commissioning standard: require every new or moved meter to be commissioned with a clamp-meter check of ratio, polarity and circuit, and recorded in the metering schedule.
• Validation rules in the data platform that flag gaps, flat lines, negative readings and reconciliation differences automatically.
• Tenant recharge corrections: recalculate past bills where errors are found, and agree adjustments.
• Open data formats so metering data can move between platforms when vendors change.

Audits are lump sums. Meter corrections are itemised. Meter replacement and additions are per meter plus installation and communications. Data platforms are recurring subscriptions. Errors corrected in tenant recharges can produce refunds or recoveries.

Billing compliance is code compliance; metering for ratings is often code compliance or improvement; replacement is lifecycle; corrections are repairs and maintenance.

Correcting long-standing billing errors can involve refunds to tenants for overcharging or unrecovered costs for undercharging, which may exceed the cost of fixing the meters.

• Australia. Meters used for trade must meet national measurement law administered by the National Measurement Institute; embedded networks are regulated by the Australian Energy Regulator with state rules, and Victoria is restricting new embedded networks in residential buildings; NABERS requires metering to rate buildings; the National Construction Code requires energy monitoring facilities in larger new buildings.
• United Kingdom. The Measuring Instruments Regulations 2016 govern billing meters; the Heat Network (Metering and Billing) Regulations 2014 require meters on heat networks; Approved Document L and CIBSE TM39 guide metering in non-domestic buildings.
• United States. State public utility commissions regulate sub-metering and re-billing of utilities to residents; weights and measures authorities oversee meter accuracy; benchmarking and building performance standards in many cities require whole-building data that sub-metering supports.

• Metering schedule and single-line diagrams.
• Meter approvals and verification certificates for billing meters.
• Reconciliation reports.
• Tenant recharge methods and disputes.
• Embedded network registrations, exemptions and compliance records.
• Data platform contracts and access.

• Commissioning records for each meter.
• Data platform validation reports.
• Records of loads added since metering was designed.