Sub-metering a live building: what the installation actually involves

Most monitoring proposals describe the platform. Almost none describe the fortnight before the platform has anything to show you. That fortnight is what a facilities manager, a plant engineer or a hospital estates officer actually has to approve, because it is the part that touches a live electrical installation in a building that cannot simply stop.

So this article is about the installation, not the dashboard. The programme below is the one Orijtech works to, drawn from our own commissioning schedule for a multi-point industrial deployment: roughly fifteen working days from order placement to signed handover, inside a three-week purchase order lead time.

The short answer on disruption

Sub-meters are measurement devices fitted alongside your existing switchgear. They do not carry your load, and nothing downstream is re-routed through them. Each three-phase meter takes its readings from two connections: a set of current sensors that clamp around the conductors, and a voltage tap.

What that means in practice:

• There is no site-wide shutdown. There is no stage of this work that requires the whole building to go dark.
• There are brief planned isolations, one metering point at a time. Fitting a current sensor and landing a voltage tap requires the board being metered to be dead for that window. A board serving a floor, a chiller or a production line is isolated; the rest of the site keeps running.
• You choose the windows. Isolation times are agreed with your engineering team before mobilisation, not negotiated on the day. Hospitals push them to the shoulder of a shift, hotels to low-occupancy hours, factories to a planned maintenance slot.

That is the entire physical intrusion. Everything else is mounting, wiring within the enclosure, configuration and verification.

The programme, stage by stage

Days 1 to 9 — procurement, before anyone reaches site

• Day 1 — equipment order placed; specifications, quantities and delivery timeline confirmed with suppliers.
• Day 2 — supplier acknowledgement; provisional installation dates and isolation windows agreed with your engineering team.
• Days 3 to 8 — supply, manufacture and transit; shipment tracked.
• Day 9 — goods received and inspected; meters and gateway pre-configured and bench-tested before mobilisation.

The item worth noticing is day 9. Meters are configured and tested on the bench, not in your switch room. Every hour of setup done before mobilisation is an hour your electrical room is not occupied.

Days 10 to 15 — on site

• Day 10 — mobilisation, safety induction, permit to work. Mounting positions and isolation windows confirmed; conductor and busbar sizes checked for coil fitment.
• Days 11 and 12 — mechanical installation, point by point: DIN-rail enclosures, isolators, trunking and conduit, voltage-tap wiring, and three sensors per meter with orientation and phase mapping verified. The gateway is mounted and powered at a central position with cellular coverage.
• Day 13 — generator fuel monitoring, where it is in scope: tank sensor, transmission unit, converter, enclosure and engine-hours wiring.
• Day 14 — power-up. Readings verified, phase rotation and sensor direction checked, meters paired to the gateway, links confirmed, dashboards configured and each point labelled.
• Day 15 — twenty-four-hour data-integrity check, functional tests, snag closure, commissioning sign-off, and handover of the as-installed record.

Day 14 is where a badly executed installation is caught and a well executed one is proved. Sensor direction and phase mapping are the two errors that produce a dashboard which looks plausible and is wrong — negative power on a healthy feeder, or a phase imbalance that exists only in the wiring of the meter. They are checked at power-up, then checked again against twenty-four hours of real data before anyone signs anything.

Three current sensors per meter. Always.

A three-phase meter requires three current sensors, one per phase. This is not a preference and it is not a premium option.

It is worth being blunt about why, because quotations offering two sensors per three-phase meter do circulate in this market. A meter that measures two phases and infers the third cannot show you phase imbalance — and imbalance is one of the most common and most damaging findings in Ugandan facilities. It overheats one winding of a transformer while the others sit idle, it trips protection for reasons nobody can explain, and it quietly consumes capacity you have already paid for. A meter that cannot see it has removed the single finding most likely to justify the project.

So when you compare quotations, count the sensors. The arithmetic is fixed: sensor quantity equals meter quantity times three.

Choosing the tier — by current, not by importance

Meters are selected by the current the monitored circuit actually carries, not by how important the load is to the business.

• Light Tier — up to 100A per phase, on a 100A split-core current transformer of 13mm. Lighting and socket boards, small pumps, small office loads.
• Medium Tier — up to 600A per phase, on a 600A split-core current transformer of 32mm. Lifts, boilers, compressors, HVAC panels, floor distribution boards.
• Heavy Tier 1000 — up to 1000A per phase, on a 1000A Rogowski coil of 100mm. Transformers, main incomers, large chillers, large feeders.
• Heavy Tier 2000 — up to 2000A per phase, on a 2000A Rogowski coil of larger diameter. Very large transformers, high-capacity industrial incomers.

Light and Medium Tier units are accuracy class 0.5 to IEC 62053-21 — within 0.5 percent. Heavy Tier units are class 1 to IEC 62053-22, better than 1 percent above 5A. Split-core transformers clip around a cable; Rogowski coils are flexible and wrap busbars that a rigid transformer cannot physically reach, which is why the incomer tiers use them.

One caveat we state in every assessment and every quotation: final sensor sizing is confirmed on site. Conductor diameter, busbar geometry and the space available inside the enclosure decide what physically fits, and none of those can be established from a drawing or a phone call. A supplier who fixes sensor sizing before a survey is guessing and will be back.

Gateways, and why they decide the layout

Meters report to a gateway, and the gateway is what carries data off the site. The rule is one gateway per physical monitoring location, not one per meter and not one per building.

Meters in the same electrical room share a gateway. A separate building, a distant plant room or a basement with no signal needs its own. Gateways are mounted centrally within the group they serve, so wiring runs stay short, and they need two things at that position: power, and reliable cellular coverage.

This is worth raising early, because it is the constraint that most often changes a metering layout. A basement switch room with no signal is a solvable problem, but it is much cheaper to solve during the survey than on day 14.

What we need from you

Every schedule states these explicitly, and they are the items that slip programmes when they are assumed rather than agreed:

• Safe access to electrical rooms, distribution boards and plant areas.
• Agreed isolation windows for each metering point.
• A gateway mounting position with power and cellular coverage at each monitoring location.
• Access to generators and fuel tanks, where fuel monitoring is in scope.
• A nominated engineering representative to witness commissioning and sign off the as-installed record.

That last one matters more than it looks. The as-installed record — which meter is on which board, which sensor is on which phase, what each point is named — is the document that makes the data defensible a year later, when somebody queries a number in a report and the engineer who was there has moved on.

After handover: the baseline

Commissioning is not the end of the work; it is the point at which the measurement starts. The first job after handover is collecting a baseline — a full operating cycle of real data, covering working days, weekends and whatever your facility does at night.

Until that baseline exists, nothing can be honestly compared to anything. After it exists, a solar system can be sized against measured consumption rather than a bill estimate, an audit can point to a reading instead of an opinion, and a savings claim can be checked.

That is the whole argument for metering the building first: everything else Orijtech does is only as good as the record underneath it.

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Sources: Orijtech Energy installation and commissioning schedule (multi-point industrial deployment); Orijtech meter tier specification. The fifteen-day programme is a documented delivery template, not a contractual commitment — site conditions, isolation availability and shipping vary, and your own schedule is agreed before mobilisation.

Request a site assessment and we will tell you how many metering points your facility needs, where they go, and what your isolation windows would have to be.