3-Phase Energy Meter for Home Assistant — ENM-223-R1, DIN Rail, Modbus RTU

Tech Specs

Installation, Environmental & Mechanical

Home Assistant / Modbus / Web Config Integration

The ENM-223-R1 supports flexible integration with:

• HomeMaster MicroPLC and MiniPLC controllers
• PLC and SCADA systems via Modbus RTU
• Home Assistant using ESPHome (controller side) or a Modbus integration
• Direct USB-C configuration using browser-based WebConfig

Configuration (metering options, calibration/offsets, alarms, relay modes, LED/button mapping) is saved persistently and restored at power-up.

Quick Setup Process (USB-C WebConfig)

1. Mount & Power – Install on DIN rail and connect the 24 V DC supply.
2. Connect USB-C – Connect USB-C cable to the module.
3. Open WebConfig – Open WebConfig in Chrome/Edge.
4. Connect Device – Click Connect and select the serial device.
5. Configure Modbus – Set Modbus address and baud rate.
6. Meter Calibration & Alarms – Select line frequency, scaling, and thresholds per phase.
7. Map Relays/LEDs/Buttons – Choose relay control mode and alarm/ack behavior.
8. Save & Disconnect – Save settings and disconnect USB-C for field operation.

Typical WebConfig options:

• Modbus address (1–247) and baud rate (9600–115200)
• Line frequency (50/60 Hz) and metering sum mode
• Per-channel gains/offsets (U/I calibration)
• Alarm / warning / event thresholds with optional acknowledgment behavior
• Relay control modes (alarm-controlled or Modbus-controlled) and inversion
• User LED sources (alarms/warnings/events/overrides)

WebConfig provides live meter values and configuration settings (stored persistently).

uart:
  id: uart_modbus
  tx_pin: 17
  rx_pin: 16
  baud_rate: 19200
  parity: NONE
  stop_bits: 1

modbus:
  id: modbus_bus
  uart_id: uart_modbus
  turnaround_time: 100ms
  send_wait_time: 250ms

packages:
  enm1:
    url: https://github.com/isystemsautomation/homemaster-dev
    ref: main
    files:
      - path: ENM-223-R1/Firmware/v0.2.0/default_enm_223_r1_plc/default_enm_223_r1_plc.yaml
        vars:
          enm_prefix: "ENM #1"
          enm_id: enm_1
          enm_address: 3 # Modbus address set in WebConfig
    refresh: 1d

Connectors & terminal map

Top row (24Vdc | CT | VOLTAGE)

Bottom row (RS-485 | RELAY OUTPUT | CT)

Ports & service interfaces

Housing notes

• CT1 is on the BOTTOM row while CT2 and CT3 are on top.
• CT polarity order differs by row: the top blocks read (-,+), CT1 reads (+,-).
• Voltage input descends L3 L2 L1 from right to left.
• Current-output CT only, secondary <=60 mA RMS. A 1 A or 5 A CT will destroy the module.
• Never open a live CT secondary.

Cabling and Wirings

24 V DC Supply (V+ / 0V)

Connect + to V+ and − to 0V; use appropriate protection upstream.

• Power is SELV-rated and supports reverse-polarity protection
• Route power wiring separately from mains and sensor wiring
• Apply terminal strain relief and maintain cabinet segregation

Voltage Inputs (L1 / L2 / L3-N / PE)

Connect mains sensing inputs and protective earth (PE) per the terminal map. Voltage inputs can be hazardous.

Current Transformers (CT1 / CT2 / CT3)

External current-output CT, ≤ 60 mA RMS secondary. Set CT ratio and PGA in WebConfig. Shielded pairs recommended.

Relay Outputs (NO / COM / NC)

Dry contact wiring only — external load supply and protection are mandatory.

RS-485 / Modbus RTU

Terminal order differs across the HomeMaster range. Always read the silkscreen - do not wire by habit from another module. On this module the order is B-A-COM. Swapping A and B damages nothing but the node will not communicate. COM is required on every node.

All HomeMaster controllers and modules share the same RS-485 front end.

Bus wiring rules — apply to every device on the bus:

• One twisted pair for A/B, 120 Ω characteristic impedance.
• Run COM to every node. Required, not optional: the ports are not isolated, and COM is what bounds the common-mode voltage the transceivers see.
• Prefer one power supply for the whole bus, distributed in star topology. With separate supplies, additionally tie the 0 V references together at a single point.
• Bond the cable shield to cabinet PE at one end only. Never land a shield on A, B or COM.
• Where the bus crosses into a different electrical installation with its own earthing reference — a utility or billing meter, another building, another cabinet's PE system — fit an external galvanic RS-485 isolator at that boundary. The on-board components are transient protection, not isolation, and will not survive a sustained ground-potential difference.

Wire A to A, B to B, and COM to every node (required).

Cable Recommendations & Shield Grounding

General Routing Rules

• Route low-level signal cables separately from mains, relay outputs, contactors, and power wiring
• If crossing power cables is unavoidable, cross at 90°
• Keep cable runs as short as practical and avoid parallel runs with high-current conductors
• Label cables and provide strain relief at terminals

RS-485 (Modbus) Cable

• Twisted pair for A/B (120 Ω characteristic impedance recommended)
• Second conductor/pair can be used as COM (0V reference) depending on the network design
• Prefer shielding for industrial/noisy panels

Shield Grounding

• Bond cable shield(s) to cabinet PE/EMC ground at the PLC/controller end only by default
• Do not connect shields to RS-485 signal terminals (A/B/COM)
• If both ends are in equipotential bonded cabinets, shields may be bonded at both ends using proper 360° clamps

System Architecture & Pinout

System block diagram showing internal architecture and interfaces.

MCU interfaces and major connector/pin reference.

Field board: voltage sensing and CT front-end connectors.

MCU board: controller + comms overview.

Safety and Installation Notes

• Qualified personnel only: Installation by trained technicians familiar with SELV and mains wiring.
• Mixed voltage domains: 24 V DC is SELV; voltage sensing inputs are mains hazardous (85–265 V AC).
• Install inside an IP20 control cabinet and protect terminals using the required front plate/door.
• Respect relay contact system limits (3 A @ 250 V AC resistive) and provide external overcurrent protection.
• For inductive/high-inrush loads: use proper suppression (RC snubbers / TVS as required).
• Use current-output CTs (secondary ≤ 60 mA RMS) — do not use voltage-output CTs (333 mV / 1 V class) or 1 A / 5 A secondaries; observe polarity and shielding to avoid incorrect metering.
• Maintain RS-485 cabling best practices: twisted pair, correct A/B polarity, and bus termination as required.

Compliance & Certifications

The ENM-223-R1 module is CE marked. ISYSTEMS AUTOMATION S.R.L. (HomeMaster® brand) maintains the technical documentation and a signed EU Declaration of Conformity (DoC) available for download in the Documents and Resources section above.

• EMC Directive 2014/30/EU — EN 55032:2015 (Class B emissions), EN 55035:2017 (immunity), tested by Idvorsky Laboratories Ltd. (Job #1648)
• Low Voltage Directive 2014/35/EU — EN 62368-1:2020 + A11:2020, in-house dielectric and isolation testing by ISYSTEMS AUTOMATION compliance laboratory
• RoHS Directive 2011/65/EU — EN IEC 63000 technical documentation
• HomeMaster® — registered EU trademark (EUTM No. 019082911, EUIPO, registered 15 January 2025)