Is B21 312-100 the same ordering code?

No. The catalogue assigns 2CMA100150R1000 to Steel B21 112-100 and 2CMA100155R1000 to Silver B21 312-100. Their shared enclosure does not establish identical metering functions.

Why does an absent phase return a normal reply?

The B21 manual says unused quantities inside the mapped range can return a normal reply containing invalid values. Unsigned quantities use all FFFF words; signed quantities use the largest positive representable value. Do not publish L2/L3 data from a single-phase meter.

Can Edge read the four-register energy counter?

The map exposes active import energy at 5000h as four unsigned registers. The current Edge Modbus client does not read 64-bit values. Keep that total on the meter display; the supported two-register electrical readings remain useful for monitoring.

ABB B21 112-100

Power and energy meter

B21 112-100, order code 2CMA100150R1000, is the two-module Steel meter with RS-485. It monitors one phase and neutral without external CTs. Edge can read voltage, current, power and frequency over Modbus RTU. Keep this exact version separate from the Silver B21 312-100 and from the three-phase B23 or CT-connected B24.

Modbus RTU

Power and energy meter

Ask an engineer

Compatibility

Compatible with EpiSensor Edge over Modbus RTU

ABB documents the built-in serial option for this ordering code and a B21 FC03 map with literal wire addresses, integer widths, resolutions and byte order.

Exact B21 112-100, 2CMA100150R1000, single phase and neutral. Use B21 manual revision D as the starting map. Confirm the nameplate and serial configuration, then compare one voltage read with the display before adding points. Do not poll missing phases or inherit Silver-version features.

Connect it with

For the built-in serial port on B21 112-100

Modbus
Edge
Platforms

Select Modbus rather than EQ bus in the RS-485 menu. Match address, baud rate and parity with the approved isolated serial adapter. Keep one master and follow ABB’s bus wiring and termination instructions. The customer-platform output is optional; Edge remains the local system of record.

Models

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Models	Interface	Route into Edge
B21 112-100 / 2CMA100150R1000	Steel, single-phase direct 65 A, pulse output and built-in RS-485.	Use the meter’s Modbus serial setting through an isolated interface to the Gateway.
B21 111-100 / 113-100 / 312-100	111 has no wired serial option; 113 is M-Bus. Silver 312 is a separate RS-485 model, order code 2CMA100155R1000.	Do not exchange ordering codes or infer Silver tariffs/reactive features, Ethernet or three-phase inputs for the chosen 112 meter.

Specifications

The Steel leaflet and ordering catalogue bind RS-485 B21 112-100 to code 2CMA100150R1000. The newer B21 manual supplies the protocol. Its shared table includes quantities for other variants, so the poll remains limited to supported single-phase electrical values.^1, 2, 3

Exact model: B21 112-100, 2CMA100150R1000; Steel version, single phase plus neutral, two DIN modules.^2, 3
Direct inputs: 230 VAC nominal; 220–240 VAC range with −20%/+15% tolerance. Base current 5 A, maximum 65 A; no external CT input.^1, 2
Accuracy and supply: Active energy class B (class 1); voltage circuit consumption 0.9 VA / 0.4 W. The meter is supplied from its measurement circuit.^1, 2
Serial configuration: Modbus address 1–247, 1200–115200 bit/s, none/odd/even parity. The menu also offers EQ bus, which is a different protocol.¹
Installation envelope: 35 × 97 × 65 mm; −40 to +70 °C. Terminals IP20 without protective enclosure; IP51 in the specified protective enclosure. Follow the manual’s humidity limits.^1, 2
Read limits: FC03 reads 1–125 consecutive registers. Multi-register values place the most significant byte at the lowest address; the published hexadecimal start address is sent unchanged.¹

Interface

Documented measurements and integration boundaries for B21 112-100.

Voltage L1-N: 5B00h, two unsigned registers, resolution 0.1 V. Current L1: 5B0Ch, two unsigned registers, resolution 0.01 A. These are literal wire addresses.
Total active power: 5B14h, two signed registers, resolution 0.01 W. Frequency: 5B2Ch, one unsigned register, resolution 0.01 Hz. Only add values that the single-phase Steel meter supports.
Total active import energy at 5000h uses four registers with resolution 0.01 kWh. Edge’s Modbus client does not read this 64-bit quantity. Keep the energy total on the meter display rather than reading half a counter.

Assessment

Exact B21 112-100, 2CMA100150R1000, supported single-phase values only.

InteroperabilityWell supported: The exact ordering table supplies RS-485 and the B21 manual defines FC03, literal wire addresses, widths, resolution and byte order.^1, 2
AccuracySupported with conditions: The direct-connected 65 A Steel meter measures active energy to class B/class 1. Supported electrical values fit Edge’s read width, while the four-register energy total does not.^1, 2
SecurityLimited: The manual exposes both read and write function codes over ordinary serial Modbus. Restrict physical and network access and exclude all configuration, reset and output commands from monitoring.¹
ReliabilitySupported with conditions: The meter is powered from the measured circuit. The protocol defines invalid unsigned/signed values; handle these and communication interruptions explicitly instead of substituting zero.^1, 2
RuggednessSupported with conditions: ABB specifies −40 to +70 °C, IP20 terminals without enclosure and IP51 in a protective enclosure, with humidity limits. Select the cabinet and wiring for those conditions.^1, 2
ScalabilitySupported with conditions: Selectable addresses and serial rates support multi-meter polling. FC03 permits up to 125 registers; budget the bus and keep unsupported phases and variants out of the point set.¹
LifecycleSupported with conditions: The dated Steel leaflet and ordering catalogue establish the exact code, while revision D provides a B21-specific starting map. Retain serial settings, installed identity and source revision when replacing the meter.^1, 2, 3

Setup

Check one single-phase voltage read

B21 manual section 9.3 lists L1-N voltage at 5B00h, two unsigned registers with 0.1 V resolution. Section 9.2 defines the multi-register order.

Function: FC03 Read Holding Registers
Wire address and length: 5B00h = 23296 decimal; 2 registers
Request PDU: 03 5B 00 00 02
Synthetic response data: 00 00 08 FC → unsigned 2300 × 0.1 = 230.0 V
Acceptance: Compare with the simultaneous L1-N voltage display. Retain both words and reject FF FF FF FF as unavailable.

Acceptance: These are calculated bytes from the documented B21 format, not a physical device capture. The RTU client adds the configured meter address and CRC. Do not decode the integer as Float32 or apply a second address conversion.

Confirm the direct-connected version
Have the authorised installer verify the exact order code, single-phase circuit, current limit and wiring. This is not a CT meter. Follow ABB’s isolation and terminal instructions before any wiring change.
Match the serial menu
In SET > RS-485, select Modbus and record the actual address, baud rate and parity. Match these in Edge through the isolated serial interface. Do not leave EQ bus selected.
Send the literal voltage address
Read L1-N voltage with FC03, start 5B00h (23296 decimal), length two registers. Section 9.3 explicitly says the hexadecimal address is sent on the bus as printed: do not subtract 40000 or decrement it by one.
Decode and check unavailable values
Combine both words as one unsigned 32-bit integer with the most significant byte and word first, then multiply by 0.1 for V. All-FFFF words mean invalid unsigned data. Signed two-word quantities use 7FFFFFFF as the invalid marker. Compare the fresh voltage with the display.

Common questions

Is B21 312-100 the same ordering code?: No. The catalogue assigns 2CMA100150R1000 to Steel B21 112-100 and 2CMA100155R1000 to Silver B21 312-100. Their shared enclosure does not establish identical metering functions.^2, 3
Why does an absent phase return a normal reply?: The B21 manual says unused quantities inside the mapped range can return a normal reply containing invalid values. Unsigned quantities use all FFFF words; signed quantities use the largest positive representable value. Do not publish L2/L3 data from a single-phase meter.¹
Can Edge read the four-register energy counter?: The map exposes active import energy at 5000h as four unsigned registers. The current Edge Modbus client does not read 64-bit values. Keep that total on the meter display; the supported two-register electrical readings remain useful for monitoring.¹

Sources

At a glance

Interfaces: Modbus RTU
Class: Power and energy meter
Manufacturer: ABB

Assessment

Interoperability 3

Accuracy 2

Security 1

Reliability 2

Ruggedness 2

Scalability 2

Lifecycle 2

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ABB B21 112-100

Compatibility

Connect it with

Models

Specifications

Interface

Assessment

Setup

Check one single-phase voltage read

Common questions

Related devices

Sources

Further reading

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