Home Assistant integration for Eastron SDM energy meters reached over a Modbus-to-Ethernet gateway (RTU over TCP). Several meters share one gateway; each is addressed by its Modbus slave address and appears in Home Assistant as its own device under a name you choose.
Supported meters:
| Model | Meter code | Phases |
|---|---|---|
| SDM120 | 0x0020 |
1P2W |
| SDM630 | 0x0070 |
3P4W |
Home Assistant 2025.6.0 or newer. The reactive energy counters use the
reactive_energy device class, which was added in that release; on older
versions Home Assistant rejects those six sensors.
The integration ships its own brand icon in custom_components/eastron_modbus/brand/.
Home Assistant only reads local brand images from 2026.3 onwards; on older
versions the icon is simply not shown and everything else works unchanged.
Add this repository as a custom repository of type Integration, install Eastron SDM Modbus, then restart Home Assistant.
Copy custom_components/eastron_modbus into your Home Assistant
config/custom_components/ directory and restart.
Settings → Devices & Services → Add Integration → Eastron SDM Modbus
- Enter the gateway's host and port (default
8899) and the poll interval. The gateway must be configured for RTU over TCP — not Modbus TCP. - For each meter, enter its Modbus slave address and a name. The integration probes the address, detects the model from the meter's own identity registers, and refuses addresses where nothing answers.
- Repeat until every meter is added.
The entry's Configure option opens a menu to change the poll interval, add a meter, or remove one. Removing a meter deletes its device, entities and their history; the other meters on the same gateway are untouched. A single meter can also be removed straight from its device page with Delete device, which works even while the entry fails to load. The last meter of a gateway cannot be removed — delete the integration entry instead.
A meter that stops answering is skipped with a warning instead of taking the whole gateway down: the other meters keep polling, and the missing one can be removed. Only when no meter at all answers is the entry retried, since that points at the gateway rather than at a meter.
All meters behind one gateway share a single TCP connection and one lock, because the gateway funnels them onto a single RS485 bus. Only one request is in flight at a time, with a short gap between requests.
Each meter is polled by its own coordinator. Reads are grouped into blocks of adjacent registers — the meters cap one response at 40 registers, so a full SDM630 refresh costs 6 requests and an SDM120 costs 4, rather than one per value. Measured against real hardware: 1.4 s for the SDM630, 0.7 s per SDM120.
Entities are keyed by the meter's hardware serial number rather than its slave address, so history survives readdressing a meter on the bus.
RS485 has no arbitration between masters. If something else polls the same
meters — a leftover modbus: block in configuration.yaml, another gateway
client, a vendor tool — the two masters' frames interleave and each sees
truncated replies and timeouts. Truncated reads are rejected rather than
decoded into wrong values, and the log then asks whether another master is on
the bus. Remove the other poller; there is no setting that makes sharing work.
Most registers are created disabled by default; see Entities below for what is enabled and how to turn on the rest.
The SDM120 exposes 18 values and the SDM630 62, but most are created disabled so a fresh install stays readable. Enabled by default are the everyday quantities — voltage, current, power, power factor, frequency and the import and export energy counters:
| Meter | Enabled | Total |
|---|---|---|
| SDM120 | 7 | 18 |
| SDM630 | 19 | 62 |
On the SDM630 those are the per-phase values (L1/L2/L3) plus the averages and system totals for power and power factor.
Everything else — apparent and reactive power, reactive energy, the total energy registers, line-to-line voltages, neutral current, THD, demand figures, phase angles, apparent energy, ampere hours and the per-phase energy counters — is created but disabled. Enable what you need per entity on the device page.
Each meter also carries six diagnostic entities reporting how its own polling is going. They live under Diagnostic on the device page and are enabled by default, since they are what tells you a meter has gone quiet:
| Entity | Meaning |
|---|---|
| Poll status | ok, timeout (nothing answered), invalid (truncated frame — usually a second master on the bus) or error. Carries the last error text as an attribute. |
| Poll duration | How long the last full refresh took, in milliseconds |
| Last successful poll | Timestamp of the last good read |
| Consecutive failures | Resets to zero on the next success |
| Failed polls | Running total since Home Assistant started |
| Poll success rate | Share of polls that succeeded, in percent |
Unlike the measurement entities, these stay available while a meter is failing — otherwise they could not report the failure.
Device classes follow Home Assistant's own validation tables:
| Values | Device class | State class |
|---|---|---|
| Voltage, current, power, apparent/reactive power, frequency | matching class | measurement |
| Power factor | power_factor (unitless) |
measurement |
| kWh counters | energy |
total_increasing |
| kvarh counters | reactive_energy |
total_increasing |
Active energy counters can be used directly in the Energy dashboard.
Four value types carry a unit but no device class, because Home Assistant has no matching one: apparent energy (kVAh), ampere hours (Ah), THD (%) and phase angle (°). Assigning a device class to these would make Home Assistant reject the state.
The register maps were transcribed from the Eastron protocol specifications and verified against live hardware:
docs/SDM120-MODBUS_Protocol.pdf— SDM120 V2.4docs/SDM630_MODBUS_Protocol.pdf— SDM630 V1.8
All measured values are 32-bit IEEE-754 floats spanning two input registers, read with function code 04, most significant register first.
The PDFs are vendor documents and are not redistributed here; they are kept
locally in docs/ and excluded from the repository.
Every version and its changes are listed in the changelog.
This project is not affiliated with Eastron Electronic Co., Ltd. "Eastron" and "SDM" are trademarks of their respective owners. Use at your own risk.