Energy meter ABB TERRA AC B21 112-100 single-phase 5 A Modbus RS485

ABB TERRA AC B21 112-100 is a compact DIN-rail single-phase energy meter with a backlit display. Designed for residential and commercial installations, it supports direct connection in single-phase systems and can be used in 3- or 4-wire configurations. The meter provides active energy measurement, multiple instrumentation values, event logging and up to 25 configurable alarms. It features one programmable output for pulse or alarm signaling and RS-485 communication over Modbus RTU or EQ Bus. The device meets IEC and MID requirements and has accuracy class 1.0 (class B for MID meters).

Advantages

The meter combines a small 35 mm width with a readable backlit LCD for space-efficient panel mounting while keeping measured values accessible. Built-in Modbus RS-485 enables remote readout and integration into building energy management systems. A single programmable output and extensive alarm/event logging support local automation and fault indication. Polycarbonate housing with transparent front and IP20 protection ensures robust electrical insulation and safe installation inside distribution panels.

Suitable for

• Residential electrical energy monitoring
• Commercial and small industrial consumption metering
• Panel mounting in distribution boards and metering cabinets
• Integration with building management systems via Modbus RS-485

Key specifications

• Connection: single-phase direct connected, suitable for 3- or 4-wire systems
• Nominal input current: 5 A
• Nominal input voltage: 220–240 V
• Frequency range: 50 / 60 Hz
• Power consumption: 0.414 W
• Communication interface: Modbus RTU over RS-485 (also supports EQ Bus)
• Output: one programmable pulse/alarm output
• Accuracy class: 1.0 (or class B for MID meters)
• Display: backlit LCD
• Material: polycarbonate front (transparent glass), glass-reinforced polycarbonate upper and bottom case, polycarbonate terminal cover
• Ingress protection: IP20 (for indoor panel installation)
• Dimensions (W×H×D): 35 × 26.5 × 65 mm
• Weight: 150 g

How to use

Mount the ABB TERRA AC B21 on a standard DIN rail inside a distribution board. Connect the phase and neutral conductors according to the 1-phase wiring diagram and ensure the nominal voltage and frequency match the installation. Connect the RS-485 interface for remote reading if required and configure Modbus parameters (baud rate, address, parity) to match the host system. Use the onboard menu and backlit display to view energy, power and other measured values and to configure alarms and the pulse output.

Usage recommendations

Install the meter in a dry, indoor distribution panel with IP20-rated protection and ensure correct polarity and secure terminal connections. Verify Modbus settings before commissioning and log measured values regularly when integrating into energy management systems. For MID verification or billing applications follow local regulations and calibration procedures.