Electrical sub-meter : Definition

15 February 2024
3 min

What is an electrical sub-meter?

An electrical sub-meter is a device associated with the main electrical meter.

While the main meter provides an overall view of a building's electricity consumption, the electricity sub-meter precisely records the electricity consumed by specific areas and uses within the building.

The installation of electrical sub-meters is often part of an energy optimisation strategy. It encourages proactive management of resources and a more detailed understanding of a building's consumption habits. It's the first step towards intelligent, economical energy management.

Note: sub-metering is not limited to electricity. It can also be used to measure water and gas consumption, providing an overall view of the use of energy resources in a building (or group of buildings).

The different types of sub-meter

1. The anatomy of the electricity meter

- The single-phase or three-phase sub-meter:

The electricity sub-meter can be single-phase or three-phase. In reality, this is not a choice at all, as it is dictated by the initial configuration of your electrical installation.

You need to adapt your sub-meter to the characteristics of your electricity supply and the power associated with your general meter.

- The communicating sub-meter:

For automated information management, electronic sub-meters incorporate communication functionalities (whether single-phase or three-phase).

Unlike traditional sub-meters, smart sub-meters use different communication technologies (wired or wireless) to automatically transmit data, without having to read it on the equipment in real-time.

Some smart sub-meters are equipped with data storage and processing capabilities. They can then process consumption information locally to generate detailed reports: consumption trends, anomalies, and peaks in demand.

2. The different communication protocols

- Wired communication (Modbus):

Wired communication protocols such as Modbus RTU enable reliable transmission of data, without the risk of hazards associated with the quality of a wireless network. They are therefore often preferred for recovering electricity consumption data measured by sub-meters.

Modbus RTU is the most widely used protocol for wired solutions. It is the "standard" solution, offering the best value for money on the market.

- The Internet of Things (IoT):

Other electricity sub-meters are equipped with IoT (internet of things) functionalities. Just as reliably, they can transmit data directly to application servers or communicate with other connected equipment.

The dialogue is made possible by a specific wireless communication protocol, one of the best known of which is the LoRaWAN protocol. LoRaWAN is appreciated for its ability to operate over long distances and its low energy consumption.

This wireless technology is particularly useful when it comes to installing new equipment in existing buildings. In renovation projects, it is not uncommon for the creation of new cable routes to prove particularly complex. The IoT makes it possible to install innovative equipment without having to carry out costly adaptation work that is inconvenient for the occupants.

Read: Supervise a building's technical equipment using LoRaWAN: a solution to wiring problems.

- Specific protocols (M-Bus, KNX):

Depending on requirements and specific technical standards, dedicated protocols such as M-Bus (for water meters) or KNX (for BMS equipment) can also be used.

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