Device overview
The ABB B21 312-100 is a single-phase, direct-connected electricity meter for residential and commercial distribution boards. It combines a 65 A current path, MID Class B active-energy accuracy, a backlit display, and RS-485 Modbus RTU communication in a two-module DIN-rail enclosure.
Its strongest fit is installer-led submetering, solar import/export monitoring, tenant or branch-circuit accounting, and building-energy systems that need a standards-based local meter rather than a vendor cloud appliance.
Core characteristics
- Model: B21 312-100
- ABB product ID: 2CMA100155R1000
- Supply context: single-phase 230 V AC
- Current connection: direct, up to 65 A
- Active-energy accuracy: MID Class B / IEC Class 1
- Reactive-energy accuracy: Class 2
- Communication: RS-485 Modbus RTU or EQ Bus, plus S0 pulse functions
- Energy direction: separate import and export registers
- Installation width: two DIN modules
Installation and current-sensor setup
This model is wired directly into the measured circuit. It does not use external current transformers, so the 65 A rating is a real direct-connected circuit limit rather than a CT-dependent system estimate. That makes comparisons with clamp-based monitors straightforward: the B21 is compact and measurement-focused, but the circuit must remain within its rated current and installation requires isolation, protection, conductor sizing, and work by a qualified electrician.
A CT-operated meter is a better choice where the circuit exceeds 65 A, conductor routing prevents direct connection, or the installation needs a higher-current ratio.
Measurement and solar relevance
The meter records active and reactive energy and keeps grid import and export in separate registers. This matters for solar and other bidirectional-energy projects because an integration can distinguish energy drawn from the grid from energy returned to it.
The B21 312-100 measures and reports those values; it is not an inverter controller, export limiter, or utility settlement service by itself. Any solar-control decision still depends on the connected gateway, energy-management system, or inverter logic.
Local integration and Home Assistant
No ABB cloud service is required for normal measurement. A Modbus master can poll the meter locally over RS-485. Home Assistant can use its Modbus integration when the installation provides a compatible RS-485 adapter or gateway and the operator maps the required ABB registers.
This is standards-based compatibility, not a plug-and-play ABB Home Assistant integration. Buyers should plan for bus wiring, addressing, termination, register configuration, and entity setup.
Where it fits well
The B21 312-100 is a strong choice when a project needs:
- a single-phase 230 V DIN-rail meter
- direct measurement up to 65 A
- MID Class B active-energy accuracy
- local Modbus data ownership
- import/export registers for bidirectional energy analysis
- installer-oriented integration with a BMS, gateway, PLC, or home-automation system
Limitations and comparison notes
This is not an app-first whole-home monitor. It has no native Wi-Fi, Ethernet, mobile app, or automatic appliance detection. Remote dashboards require a separate Modbus gateway or controller.
The 65 A direct-current limit is also central to selection. Larger services may need a CT-operated ABB model or another meter family. Three-phase projects should compare an appropriate ABB B23, B24, A43, or A44 model instead of treating the B21 as phase-flexible.
Purchase and source notes
ABB's current product record and energy-meter catalog identify the exact B21 312-100 / 2CMA100155R1000 model. The ABB Netherlands channel listing showed the product as current, with a EUR 420 gross list price and an indicative lead time, but regional net price, stock, certification, and delivery should be confirmed with ABB or an authorized distributor before purchase.