Skip to main content
Tech OVN

November 2026 · Energy Metering

What Is a Dual Source Energy Meter?

Reviewed by Ramniwas Gautam, Validation Head, Tech OVN

A dual source energy meter is one meter that records energy from two supplies — usually the grid (EB) and a diesel generator (DG) — in separate registers. You get a grid kWh reading and a DG kWh reading from the same device, instead of one number that mixes both.

Why separate grid and DG energy at all?

Most Indian factories, hospitals, malls and commercial buildings keep a DG set for power cuts. When the grid fails, a changeover moves the load to the generator, and the same cables, CTs and meter carry the current. An ordinary energy meter keeps counting — it has no idea the source has changed. At the end of the month, the kWh on the meter is a blend of grid units and DG units.

That blend hides the most expensive energy on the site. DG power is usually priced very differently from grid power — it is paid for in diesel, maintenance and run-hours, not on the DISCOM bill. If you can't see how many units the DG supplied, you can't work out what each DG unit cost, whether the generator is running efficiently, or how much of a department's consumption happened during an outage.

A dual source meter fixes that at the point of measurement. Grid energy and DG energy accumulate separately, so the split is already done when you read the meter.

How a dual source energy meter works

The measurement itself is the same as any 3-phase meter — voltage and current on each phase, through CTs on larger loads. What changes is where the energy is counted.

  1. Install on the common feeder. The meter sits after the changeover, on the circuit that both grid and DG feed.
  2. Tell it which source is live. The meter typically receives a signal from the changeover switch, AMF panel or ATS that indicates when the DG is supplying the load. How this is wired varies by meter and panel — confirm it with your supplier.
  3. Count into the right register. While the grid is live, energy goes into the grid registers. When the DG takes over, it goes into the DG registers. Each register set usually carries kWh, and on better meters kvarh and kVAh too.
  4. Read both sets. On the display, over Modbus or MQTT, or in an energy platform that shows grid and DG side by side.

This is different from a net meter, which records grid import and export for rooftop solar and belongs to the DISCOM side of your installation. A dual source meter sits behind the utility meter and only separates the supplies feeding your own load.

What the separate DG reading lets you do

Cost DG power properly

Divide the diesel bought in a month by the DG kWh recorded, and you have your actual cost per DG unit — a number most sites only estimate. Our diesel genset vs grid cost calculator shows how to compare it with your grid tariff.

Check generator efficiency

Units generated per litre of diesel is the simplest health check on a DG set. Tracked month to month from metered DG kWh, a falling figure is an early sign the set needs attention — or that it is running lightly loaded for long periods.

Allocate cost fairly

When departments, production lines or tenants share a supply, a dual source meter on each feeder shows who used DG power and how much. That is the basis of fair sub-metering for business on sites with frequent outages.

See how often you really run on DG

DG energy over time is also a record of supply reliability. It gives you hard data when you discuss outages with your DISCOM or plan for solar, batteries or a larger DG.

What to check before you buy one

  • Which registers are separated. kWh only, or kvarh and kVAh as well? If your tariff bills on kVAh, you want kVAh split by source too.
  • How source detection is wired. Ask exactly what signal the meter needs from your changeover or AMF panel, and who wires it.
  • Accuracy class. Class 0.5S (IEC 62053-22) is a sensible choice for C&I sub-metering; it is specified down to 1% of rated current, which matters on lightly loaded feeders.
  • Communication. Modbus RTU/TCP or MQTT, with a published register map, so both register sets reach your BMS, SCADA or dashboard without a gateway.
  • Prepaid or post-paid. Prepaid dual source meters are built for collecting money from residents. For a factory or commercial building, a post-paid monitoring meter is usually what you need.

For the wider buying checklist — CTs, mounting, phases — see our 3-phase energy meter buyer's guide.

Titan as a dual source energy meter

Titan is a Class 0.5S, 3-phase DIN-rail meter that takes a 12 V signal when the DG is on and, while it is present, records energy in a separate DG register set. It keeps grid and DG register sets — kWh, kvarh and kVAh, per phase and total, for import, export and net. Both sets are readable over Modbus RTU/TCP and MQTT; the full register map is in the public Titan integration guide.

With the Energy Management System, the grid and DG readings appear side by side with their costs, across every feeder and site. Tell us about your changeover arrangement and we'll confirm how Titan should be wired on your panel.

Frequently Asked Questions

Common questions about dual source energy meters, DG metering and wiring.

A dual source energy meter is a single meter that records energy from two supplies — usually the grid (EB) and a diesel generator (DG) — in separate registers. Instead of one kWh reading that mixes both, you get a grid kWh reading and a DG kWh reading from the same device.
The meter is told which source is live, typically by a signal taken from the changeover arrangement (manual changeover switch, AMF panel or ATS). While that signal shows DG, energy accumulates in the DG registers; otherwise it goes to the grid registers. The exact wiring depends on the meter and your panel, so confirm it with the supplier before installation. Tech OVN's Titan, for example, takes a 12 V signal when the DG is on.
Not if the grid and DG feed the same load through a changeover. In that case a single dual source meter on the outgoing side records both supplies separately. Separate meters make sense when the DG has its own feeder, or when you want to measure the DG's own output at the generator terminals.
A net meter records energy imported from and exported to the grid — it is used with rooftop solar and is installed by or for the DISCOM. A dual source meter separates two supplies (grid and DG) feeding your load. They solve different problems and are not interchangeable.
Many can. Tech OVN's Titan exposes its grid and DG energy registers over Modbus RTU/TCP and MQTT, so a BMS, SCADA or energy platform can read both sets directly. Check the register map of any meter you are considering.
That is one common use — societies and malls use dual source (often prepaid) meters to charge occupants separately for grid and DG units. This guide focuses on commercial and industrial sites, where the same separation is used to cost DG power and check generator efficiency.

Related reading

Titan Smart Energy Meter

Class 0.5S 3-phase meter with separate grid and DG registers.

Learn More →

Diesel Genset vs Grid Cost Calculator

Work out what each DG unit costs you against the grid tariff.

Learn More →

3-Phase Energy Meter Buyer's Guide

Accuracy class, CTs, communication and mounting explained.

Learn More →

Metering a site with grid and DG?

Tell us how your changeover is set up and we'll recommend where Titan goes and how to wire it.

Get a Live Energy Monitoring DemoSee Your Facility Data in 24 HoursGet Energy Savings Estimate