Should 0x5B02 become 23297?

No. ABB states that the hexadecimal start register is expressed exactly as sent on the bus. 0x5B02 is decimal 23298; no one-based correction is applied.

Why does a float decoder give nonsense?

L1 phase voltage is an unsigned integer across two registers, with 0.1 V resolution. Reinterpretation as IEEE-754 FLOAT32 changes the meaning of those bits. Use the workbook’s data type and multiplier.

Does the shared M4M workbook mean every register works on M4M20?

No. The product-applicability column distinguishes model-dependent functions. The M4M20 manual describes basic demand and THD, while the workbook contains additional rows limited to M4M30. Select supported quantities rather than importing the entire family table.

Does Bluetooth replace the RS-485 connection?

The exact product offers Bluetooth and Modbus RTU, but this Edge integration uses the documented RS-485 Modbus interface. Bluetooth commissioning is not a claim of an Edge Bluetooth driver.

How is this different from M4M30 Modbus?

The standard M4M20 Modbus has two digital outputs and basic demand functions. The reviewed M4M30 Modbus has four programmable I/O and additional analyser quantities. Choose by the functions required at the panel, then verify the exact order code and map applicability.

Why is there no ready-made Edge template?

ABB represents unavailable unsigned quantities as all FFFF words and signed quantities as the maximum positive code for their width. These decode as finite numbers, not NaN. A prepared import must reject those exact raw codes before scaling, for every included data type. This guide supplies a bounded read check instead of claiming that unqualified numeric polling handles all unavailable states.

ABB M4M 20 Modbus setup and register map

Compatibility

Compatible through Modbus RTU

Edge reads the documented local Modbus interface through the connection path below. This is protocol compatibility, not a claim of a built-in device mapping.

Exact M4M 20 MODBUS, 2CSG251141R4051 (M4M20RS485), with conventional CT inputs. Use the mapping workbook’s M4M 20 applicability, not all rows in the combined M4M20/M4M30 map. This is a source-qualified Modbus path, not a claim of physical testing or a built-in Edge template. No ready-made template is supplied: the unavailable codes are finite integers, so ordinary numeric decoding does not reject them. Configure and verify missing-value handling for each width before relying on unattended polling.

Connect it with

Modbus Interface ZMB-3X
From €399 ex VAT Configure Modbus Interface
Gateway ZGW-20
From €899 ex VAT Configure Gateway

For exact M4M20RS485 with its configured serial address

Modbus
Wireless
Edge
Platforms

Match the meter’s configured address, speed and parity. Use one master and the documented bus wiring and end termination. Bluetooth is a commissioning interface, not the Edge measurement transport used here. The customer-platform output is optional; Edge remains the local system of record.

Models

Download

Models	Interface	Route into Edge
M4M 20 Modbus · 2CSG251141R4051	Conventional1 A/5 A CT inputs; two digital outputs; Modbus RTU and Bluetooth	RS-485 is the documented measurement route in this guide.
M4M 20 Ethernet / BACnet / Profibus	Different communications variants, despite a similar front panel	Do not assume the RS-485 variant has an Ethernet port or BACnet/IP.
M4M 20 I/O / Rogowski / M4M20-M	Additional I/O, different current sensor input or MID-specific specification	Use the exact hardware manual and relevant map applicability; no variant equivalence is claimed.
M4M 30 Modbus	Separate analyser with four programmable I/O and additional model-specific quantities	Compare the reviewed M4M30 guide if those functions matter; shared register addresses do not make the hardware identical.

Specifications

The standard Modbus version combines conventional CT metering with two digital outputs. Its manual describes basic demand and minimum/maximum demand, 25 single alarms and 32 MB flash. It is useful for panel energy monitoring without assuming the extra I/O or M4M30-only power-quality quantities in the combined register workbook.^1, 3

Exact order code: 2CSG251141R4051 / M4M20RS485⁴
Current measurement: Three conventional CT inputs; 1 A or 5 A secondary ; 50 mA–6 A measurement range without accuracy derating. Neutral current is calculated.¹
Voltage and supply: 46–400 VAC L-N and 80–690 VAC L-L measurement range, with the manual’s stated conditions; separate 48–240 VAC/DC auxiliary supply ±15%.¹
Energy accuracy: Active energy class 0.5S to IEC 62053-22 under the specified conditions. CT errors and installation errors are additional; this is not a MID claim.¹
Serial interface: Optically isolated RS-485; address 1–247; 9.6, 19.2, 38.4, 57.6 or 115.2 kbit/s; configurable parity and stop bits.¹
I/O and analysis: Two digital outputs; basic demand; THD; true-RMS measurement up to the 40th harmonic. Do not infer M4M30-only register support.^1, 3
Installation envelope: Indoor panel mounting; front IP54, terminals IP20; operating −25 to +70 °C and up to 93% relative humidity, non-condensing at 40 °C.¹

Interface

Documented measurements and integration boundaries for M4M 20 Modbus.

L1 phase voltage: literal 0x5B02, unsigned 32-bit integer, resolution 0.1 V.
Phase currents, powers, frequency and power factor, decoded using each map row’s width, sign and resolution.
Import and export energy are separate counters. Import active energy at 0x5000 occupies four registers with 0.01 kWh resolution.
THD, basic demand and minimum/maximum values supported by M4M20; check the product-applicability column before adding a family-map quantity.
Unavailable unsigned quantities use FFFF in every register; signed quantities use the maximum positive code for their width. These are missing readings, not consumption.

Assessment

Exact M4M 20 MODBUS, 2CSG251141R4051 (M4M20RS485), with conventional CT inputs. Use the mapping workbook’s M4M 20 applicability, not all rows in the combined M4M20/M4M30 map. This is a source-qualified Modbus path, not a claim of physical testing or a built-in Edge template. No ready-made template is supplied: the unavailable codes are finite integers, so ordinary numeric decoding does not reject them. Configure and verify missing-value handling for each width before relying on unattended polling.

InteroperabilityWell supported: Manufacturer protocol manual plus typed, scaled register workbook establish a complete local read path.^2, 3
AccuracySupported with conditions: Conventional CT inputs and class 0.5S active-energy measurement have defined conditions; CT and wiring error remain separate.¹
SecuritySupported with conditions: The user manual documents password-controlled configuration; protect the serial segment and omit writes from monitoring.¹
ReliabilitySupported with conditions: The manual defines 48–240VAC/DC auxiliary supply with ±15% tolerance, non-condensing conditions and a measurement refresh interval. These are installation limits, not evidence of a tested field uptime.¹
RuggednessSupported with conditions: IP54 front, IP20 terminals and −25 to +70 °C operating range define a panel-mounted installation envelope.¹
ScalabilitySupported with conditions: Unique addresses 1–247 and documented bus topology support multi-meter segments; poll complete values within a managed bus schedule.^1, 2
LifecycleSupported with conditions: ABB publishes a revision L manual and a combined map with explicit product applicability. S4M configuration requires firmware 2.6.10 or later; that app requirement is not the minimum firmware for this basic Modbus read.^1, 3

Setup

Read and scale L1 phase voltage

ABB’s communications manual gives the FC03 request at 0x5B02, and its mapping workbook defines the two-register unsigned value with 0.1 V resolution.

Function: FC03 Read Holding Registers
Literal PDU address: 0x5B02 = 23298 decimal; this is already the bus address
Quantity: 2 registers, 4 data bytes
Request PDU: 03 5B 02 00 02; the RTU client adds the configured slave address and CRC
Synthetic response data: 00 00 08 FC, most significant byte first
Decode: Unsigned 32-bit 2300 × 0.1 V = 230.0 V
Acceptance: Confirm the configured wiring supports L1-N, then compare the scaled value with the simultaneous meter display

Acceptance: The 230 V response is an independently calculated example, not a physical device capture. Never apply the 0.1 multiplier to every register: current, power, energy and status entries have their own type, width and resolution.

Match the order code and CT input
Confirm 2CSG251141R4051 and record firmware and map revision. The conventional-CT inputs require the installed 1 A or 5 A secondary and correct primary ratio. Have the authorised installer confirm phase assignment and the selected wiring system before comparing readings.
Record the actual serial settings
Open Configuration, Communication, Modbus RTU and record the address, speed, parity and stop bits. Match them in the Edge serial connection. Keep one master on the RS-485 segment and follow ABB’s bus wiring and end-termination instructions.
Use literal addresses and complete values
ABB’s Start Reg Hex is the address sent on the bus. Convert hex to decimal if the client requires it; do not subtract one. Read both registers of L1 voltage at 0x5B02 in one FC03 request.
Decode before expanding the point list
Apply unsigned 32-bit decoding, most significant byte first, and the 0.1 V resolution for the voltage example. Compare the result with the meter display, then configure each further quantity from its own type, register count and resolution.
Add supported measurements, not the whole family map
Filter the workbook by M4M 20 applicability. Add energy, power and current with their individual type, resolution and width; do not copy M4M30-only power-quality rows. Treat unavailable markers as missing data and compare an energy delta with the front display. Leave output, reset and history-selection commands out of this read-only setup.

Common questions

Should 0x5B02 become 23297?: No. ABB states that the hexadecimal start register is expressed exactly as sent on the bus. 0x5B02 is decimal 23298; no one-based correction is applied.²
Why does a float decoder give nonsense?: L1 phase voltage is an unsigned integer across two registers, with 0.1 V resolution. Reinterpretation as IEEE-754 FLOAT32 changes the meaning of those bits. Use the workbook’s data type and multiplier.³
Does the shared M4M workbook mean every register works on M4M20?: No. The product-applicability column distinguishes model-dependent functions. The M4M20 manual describes basic demand and THD, while the workbook contains additional rows limited to M4M30. Select supported quantities rather than importing the entire family table.^1, 3
Does Bluetooth replace the RS-485 connection?: The exact product offers Bluetooth and Modbus RTU, but this Edge integration uses the documented RS-485 Modbus interface. Bluetooth commissioning is not a claim of an Edge Bluetooth driver.^1, 4
How is this different from M4M30 Modbus?: The standard M4M20 Modbus has two digital outputs and basic demand functions. The reviewed M4M30 Modbus has four programmable I/O and additional analyser quantities. Choose by the functions required at the panel, then verify the exact order code and map applicability.^1, 3, 5
Why is there no ready-made Edge template?: ABB represents unavailable unsigned quantities as all FFFF words and signed quantities as the maximum positive code for their width. These decode as finite numbers, not NaN. A prepared import must reject those exact raw codes before scaling, for every included data type. This guide supplies a bounded read check instead of claiming that unqualified numeric polling handles all unavailable states.²

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ABB M4M 20 Modbus