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

The module needs a Modbus master on the bus. In a HomeMaster system that is the MiniPLC or the MicroPLC — both run ESPHome and connect to Home Assistant over the native API. To work out how many modules a panel needs and how wide it comes out, use the System Builder.

Current transformers, heat-pump circuits and load-shedding targets are sized from the installation drawing — the meter reports what those circuits draw; it does not ship with CTs or prescribe which loads to disconnect.

New to this kind of system? Two guides cover the ground: building a Home Assistant automation system and a wired ESPHome smart home.

Going deeper on this module: monitoring more circuits than your panel has room for and wiring a new house before the walls close. Related modules: the MicroPLC and the OpenTherm Gateway.

Frequently asked questions

Which current transformers do I need?

Current-output CTs with a secondary of 60 mA RMS or less, working into the 6 Ω burden on the board. Full scale is 120, 60 or 30 mA depending on the PGA setting (×1, ×2 or ×4; default ×2), which is how the CT ratio is matched to the circuit being measured. Do not fit voltage-output clamps of the 333 mV or 1 V class — they are a different device class and will read wrong. Do not fit 1 A or 5 A secondary CTs: they will destroy the module. Never open a live CT secondary.

How does it get into Home Assistant?

Through a Modbus master on the RS-485 bus. In a HomeMaster system that is the MiniPLC or the MicroPLC running ESPHome, which exposes the readings to Home Assistant over the native ESPHome API. No MQTT broker and no hand-written register map. On ESPHome 2026.7.0 and later, set turnaround_time and send_wait_time explicitly — the defaults changed in that release and a Modbus bus tuned for the old values will time out.

Can it cut a load off by itself?

Yes, within its two relay channels. Thresholds, alarm and warning events and the acknowledgement behaviour are configured in WebConfig and evaluated on the module, and a relay can be set to alarm-controlled instead of Modbus-controlled. That rule keeps running with the bus master offline. Relay rating is 3 A at 250 V AC resistive as a system limit, 750 VA at 250 V AC or 90 W at 30 V DC maximum; the outputs are not internally fused, so fit external overcurrent protection, and switch anything heavier through a contactor.

Can I bill a tenant from these readings?

No. The module is not a certified revenue meter and carries no MID approval, so its figures are for monitoring, diagnostics and automation, not for settlement or resale. Where a reading has to hold up commercially, a certified meter is required and this module sits alongside it.

Is it single-phase compatible?

Yes — populate one voltage channel and one CT channel and leave the others unused. Line frequency is selectable between 50 and 60 Hz in WebConfig, along with the metering sum mode and per-channel gain and offset calibration.

Do I have to use HomeMaster controllers?

No. The module is a standard Modbus RTU slave on RS-485, address 1–247 and baud 9600–115200 (default 19200, 8N1). Any Modbus master reaches it: a third-party PLC, a SCADA system, or your own ESP32 with an RS-485 transceiver.

Is the RS-485 port isolated?

No. It has transient protection — TVS diodes, resettable PTC fuses and fail-safe biasing — but that is surge protection, not galvanic isolation; the transceiver shares the device's logic ground. Run COM to every node on the bus, and fit an external RS-485 isolator where the bus crosses into a separate electrical installation with its own earthing reference.

How is it configured?

Over USB-C from a browser using WebConfig — Web Serial, no driver and no vendor application. Modbus address and baud rate, line frequency, per-channel gain and offset, event thresholds, relay modes and LED sources are set there and stored in on-device flash (LittleFS).

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)

Licensing. Hardware design files — schematics, PCB layouts and bills of materials — are published under CERN-OHL-W v2. Firmware and the ESPHome integration packages are published under the MIT licence. Full terms are in the LICENSE files in the HOMEMASTER repository.