From four to three DIN modules: what had to be redesigned for a compact three-phase MID meter

In a DIN-rail electrical panel, modular space is a finite resource. Every module removed from the meter is a module gained for circuit breakers, protection devices, automation devices and future spare capacity. For a residential panel, the difference between four modules and three is marginal. For a sub-distribution panel, a charging station, a server room or a battery energy storage system (where component density is high and cabinet space directly translates into installed physical width), that module is a design parameter, not a detail.

The three-phase MID energy meter in the M3PRO generation currently in production occupies four DIN modules. Its successor, coming to market during 2026, occupies three. 25% less space is not an incremental improvement. It is a dimensional change that requires rethinking the layout of the metrology front end, the input terminal block, thermal management and, almost always overlooked in a commercial datasheet but fundamental at an installer’s bench, cable routing.

The article that follows is not a product sheet. It describes the technical choices that made the new compact generation of the M3PRO line possible without sacrificing any of the accuracy, robustness or configurability parameters that defined the previous generation.

Size: what moving from four to three modules means

Compressing a three-phase MID meter from four to three DIN modules (from 72 mm to 54 mm in width, while maintaining the same class 1 accuracy requirements for active energy) is not a packaging exercise. It affects three physical layers of the design at the same time.

The first is the distance between live parts, governed by the clearance and creepage requirements derived from EN IEC 62052-11 and the product classification by overvoltage category and pollution degree. Reducing the volume initially reduces precisely these distances; recovering them requires a redesign of the main PCB geometry, physical separation between measurement and auxiliary circuits and, in some cases, additional insulating barriers inside the enclosure. This is not a cosmetic change: every millimetre lost has to be recovered elsewhere, and every recovery measure must be documented in the technical file for MID conformity assessment.

The second is thermal management. The natural heat dissipation of a four-module meter has a larger exchange area with the air inside the panel; the same product in three modules has less volume to dissipate the same power losses from the measurement circuits, the current sensors and the signal electronics. Keeping the junction temperature of critical components within the windows declared in the datasheet, across the full rated ambient temperature range, requires a review of the dissipation plan: hot-spot positioning, materials used for the internal thermal mass and possible redistribution of the thermal load between PCB areas. Here too, this is technical documentation, not marketing.

The third is the terminal block. The front end of a three-phase meter must accept four incoming conductors (L1, L2, L3, N) and three outgoing conductors (L1, L2, L3), all sized for the meter’s rated current. Reducing the available width while also reducing the maximum accepted cable cross-section would be a downward compromise. The design decision was different: retain the connection capacity by using a new terminal geometry that recovers space vertically rather than horizontally.

Cable layout: input at the top, output at the bottom

A seemingly minor choice, but the one an experienced installer recognises first, is the arrangement of the line terminals.

In the previous M3PRO line, and in a large proportion of DIN energy meters on the European market, the phase input and output terminals are both on the top side or both on the bottom side of the device. This convention forces a specific cable routing: up from the supply busbar, into the meter, out on the same side, loop underneath, then on to the load. In a crowded panel, every cable bend occupies space and is a potential source of wiring error, particularly a phase inversion, which in a three-phase system has immediate metrological consequences (incorrect apparent power, reactive energy with the sign reversed) but can easily go undetected during commissioning without dedicated instrumentation.

The new compact generation adopts the convention used by MCBs and modular protection devices: cable input at the top, cable output at the bottom. The supply line enters from above, passes straight through the meter, exits towards the load from below and continues to the protection devices. The routing is mechanically simpler, cable bends are reduced and the phase arrangement is mirrored between input and output.

The technical benefit has two levels. At installation level, wiring time is reduced and the probability of error decreases because the installer works with a layout already familiar from every other modular component in the panel. At operating level, accessibility for subsequent metrological verification – in other words, the ability to isolate the meter for testing or replacement without rebuilding complex wiring – is significantly improved.

Terminal blocks: connection capacity and push-in auxiliaries

The line terminals of the new generation accept cables with a cross-section of up to 33 mm² and a stripping length of 17 mm. These figures are above the average for the compact three-phase MID meter segment and are the result of the architectural choice described above: recover vertically the space lost through lateral compression.

The maximum cross-section is not a cosmetic figure. An energy meter intended for a nominal 80 A three-phase system requires appropriately sized cables; having margin at the terminal is what allows the installer to work safely with the cross-section actually specified by the design, without resorting to mechanical reducers or adapter leads. Those solutions introduce additional contact points, each of which is a potential source of parasitic resistance and therefore of overheating under continuous load.

A 17 mm stripping length gives the installer working margin: contact between the ferrule and the terminal is predictable, repeatable and less sensitive to variations in cable preparation. For a device intended to remain in service for ten or fifteen years, in a variable thermal environment, the quality of the initial connection is the factor that determines whether that point will remain invisible over the coming years or become the first thing that needs replacing.

The second intervention on the terminal block concerns the auxiliary connections: communication (serial bus), tariff input and optional pulse output. In the new generation these terminals use a push-in system: the wire is inserted directly into the terminal, an internal spring maintains contact pressure, and no fastening tools or screws tightened to a controlled torque are required. Installation time is reduced significantly compared with a traditional screw terminal and, importantly from an operational standpoint, the connection remains inspectable and modifiable without affecting the MID metrological seal that protects the phase terminals. Replacing a communication cable, changing the tariff input source or modifying the bus configuration are all operations that do not require the seal to be broken and therefore do not require the device to undergo metrological re-verification.

This physical separation between the sealed metrological terminal block and the accessible auxiliary terminal block is an evolution that exactly reflects the logical structure of a modern meter: the measurement core is locked down, the application layer is configurable. Seeing the same separation reflected in the product hardware is a choice that speaks to the people who install and maintain the meter, not only to those who specify it in a tender.

Display, HMI and service ergonomics

The LCD uses a negative display scheme: black background, white characters. Compared with a conventional LCD with a light grey background and dark characters, readability in artificially lit environments (the normal condition for an electrical panel in a technical room or server room) improves measurably, especially when the display is viewed from the side or in reflective conditions. This is not a change of technology (the display remains a passive LCD, with its familiar advantages of negligible power consumption and long-term reliability); it is a change of colour scheme that reflects where and how the meter is actually read in service.

The user interface (menu structure, navigation between displayed quantities and configuration parameters accessible from the front) is inherited directly from the M3PRO line. This is a deliberate choice: anyone who has installed, configured or maintained M3PRO meters finds the same menu tree, the same navigation logic and the same shortcuts in the new generation. No new technical training is required, there is no need to consult updated manuals, and installers and service partners do not need to adapt their internal procedures. The family feeling between the two generations is not an aesthetic argument: it is operational continuity for an installed base that already knows the product.

Two further details of service ergonomics complete the product design. The terminal covers of the line circuits are hinged to the meter body: they open in a single movement, remain attached to the enclosure when open and cannot be lost during wiring or maintenance. It is the kind of design choice that is noticed only during field installation, but during field installation it is noticed immediately. The side IR port, present as on the current M3PRO range, guarantees direct compatibility with all accessory communication interfaces already in the catalogue: optical readers for field diagnostics, configuration kits and data acquisition devices. The new generation does not make any existing accessory obsolete.

What this means for a panel designer, an OEM and an installer

The question to ask when evaluating the integration of the new meter into a project is not “Is it better than the previous one?”, but: “Which design parameters does this device free up, and in which contexts?”

• In an EVSE panel, where the density of modular components is high and every millimetre of cabinet width directly costs material and installed volume, saving one module for every metering line creates space that translates into additional protection devices, thermal headroom in the panel and reserve for future system evolution.
• In a BESS battery energy storage system, where the number of metering channels grows with system size and the meter panel can occupy a significant portion of the cabinet, the 25% compression is multiplied by the number of lines being measured.
• In a building or data-centre sub-metering application, where dozens of meters share the same cabinet for the internal billing of departments, users or cabinets, the cumulative space saving is dimensionally significant.
• For an installer working directly with the product, the top-input/bottom-output layout, terminals for cross-sections up to 33 mm², push-in auxiliary connections and terminal covers that cannot get lost are time recovered on every installation. That is a parameter that does not always reach panel designers, but the service partner registers immediately.
• For an OEM integrating the meter into its own system, the continuity of the HMI and IR interface means that technical documentation, configuration scripts and setup procedures already written for the M3PRO generation remain valid for the new generation without anything having to be redesigned.