The Eastron SDM630 is the most widely used budget 3-phase energy meter in European solar PV and KNX sub-metering projects. At under €100 for the MID-certified version, it delivers Modbus RTU RS-485 communication with all essential power quality parameters: per-phase voltages, currents, power, power factor, and cumulative kWh with import/export separation. This guide covers hardware setup, RS-485 bus wiring, Modbus address configuration via front panel, the key register addresses for WAGO CODESYS integration, and common wiring mistakes.

Physical installation

SDM630 mounts on 35mm DIN rail, 3 modules wide (54mm). Terminal layout (left to right on bottom terminal block): L1, L2, L3 (3-phase voltage inputs, direct connection), N (neutral), then separate terminal block for current inputs. Direct connection model (SDM630-Modbus): rated to 100A continuous, 120A peak — suitable for circuits up to 100A. For loads above 100A: use SDM630 CT input model (SDM630-Modbus-MID CT) with 5A secondary current transformers. Install CT models with the arrow on the CT pointing in the direction of current flow (from grid towards load for import-positive reading). RS-485 bus terminals: A (positive/non-inverting), B (negative/inverting), GND on right side of terminal block. SDM630 supply voltage: 100-415V AC applied between L1 and N terminals — the meter self-powers from the circuit being measured (no separate auxiliary supply needed for single-phase L1+N supply).

Front-panel Modbus configuration

Long-press the front button (3 seconds) to enter setup mode. LCD shows parameter sequence: "bAud" = baud rate (scroll: 1200, 2400, 4800, 9600, 19200, 38400 — default 9600). Press short to move to next parameter. "PrtY" = parity (nO = none with 1 stop bit, n2 = none with 2 stop bits, odd, Evn = even). "id" = Modbus slave address (1-247 — default 1, scroll using long-press to increment). Set same baud rate and parity across all meters on one RS-485 bus. Each meter must have a unique address. Recommended defaults: 9600 baud, none parity, 2 stop bits — match in WAGO CODESYS Modbus RTU master configuration. Write down each meter's address, circuit name, and terminal location for as-built documentation.

RS-485 bus wiring

Maximum 32 devices at 9600 baud without repeater. Bus topology: daisy-chain (A to A, B to B between sequential meters) — not star/T-junction. Cable: Belden 9841 or Turck RSC 485 (120-ohm impedance, twisted pair, screened). Screen connection: earth at one end only (at Modbus master/WAGO panel) — leave floating at meter end. Termination: 120-ohm resistor between A and B at the farthest meter from the WAGO controller (and also at the WAGO end if more than 10m total bus length). Without proper termination at long cable runs: reflections cause communication errors (CRC failures, timeout). Bus maximum length: 1200m at 9600 baud. Polarity: SDM630 terminal A = Modbus data+ (same as RS-485 A convention). If communication fails: swap A and B connections — the SDM630 manual uses opposite polarity labelling from some RS-485 masters.

Key SDM630 Modbus registers

All registers: function code 03 (read holding registers), float32 IEEE 754 big-endian (word order: high word first, low word second), 2 consecutive registers per value. Register 0x0000 (0) = V L1 (Volts float). 0x0002 (2) = V L2. 0x0004 (4) = V L3. 0x0006 (6) = V average. 0x000C (12) = A L1 (Amps). 0x000E (14) = A L2. 0x0010 (16) = A L3. 0x0012 (18) = A neutral (calculated). 0x0034 (52) = W total 3-phase (Watts, signed — negative = export). 0x003C (60) = var total (reactive power). 0x0046 (70) = VA total (apparent power). 0x0048 (72) = PF L1. 0x004C (76) = PF average. 0x0156 (342) = kWh total import (energy from grid). 0x0158 (344) = kWh total export (energy to grid — for solar PV). 0x0160 (352) = kWh L1. 0x0162 (354) = kWh L2. 0x0164 (356) = kWh L3. Note: SDM630 register addresses differ from Carlo Gavazzi EM340 — do not reuse EM340 CODESYS code without updating all register addresses.

WAGO CODESYS integration

In WAGO e!COCKPIT CODESYS: add 750-653 RS-485 module to 750-893 rack. Instantiate FB_ModbusRTU_Master for each SDM630: fbSDM630_1(eSlave:=1, eFunction:=FC_READ_HOLDING_REGISTERS, iStartAddress:=16#0034, iLength:=2, bExecute:=bReadTrigger); After read done: rPowerTotalW := WAGO_ModbusFloatBE(fbSDM630_1.aData[0], fbSDM630_1.aData[1]); Write to KNX: GA_Power_Circuit1 := rPowerTotalW / 1000.0; (DPT 9.002, kW). For kWh energy import (polling every 60s): iStartAddress:=16#0156, iLength:=2 → rEnergyImport_kWh → GA_Energy_Circuit1 (DPT 14.019). Polling sequence: poll one meter every 500ms, cycle through all meters — 8 meters polled in 4 seconds, well within 10-second update interval for KNX energy dashboard.