Does the SPM-4Relay work without the SPM-Main?

No. It is an expansion module on the RS-485 bus: the manufacturer states the Main and 4-Relay must be used together. The SPM-Main handles the Wi-Fi or Ethernet link and supports up to 32 modules.

Why doesn't the module come online even though the bus is wired?

Usually channel 1 has no power: per the manufacturer's wiring diagram, the L1/N1 input feeds the module itself. Energise channel 1, then check RS-485 polarity and the termination resistor on the last module.

How do I see per-line consumption and for what period?

In eWeLink each of the four channels shows current, voltage, power and kWh history; operation logs are kept for three months. The SPM-Main additionally writes statistics to microSD (8–32 GB) — over 20 years of data per the manufacturer, with reports exported from the card.

I already have breakers in the panel — what are OPS thresholds for?

A breaker protects the wiring from shorts and fault overloads, while OPS solves the business side: a power cap per tenant, delayed cut-off, minimum power as a fault alarm. The manufacturer explicitly warns that OPS is not a substitute for a circuit breaker.

How many modules can I add and over what distance?

Up to 32 SPM-4Relay modules per SPM-Main — 128 channels. The RS-485 bus runs up to 100 m over shielded RVVSP 2×0.2 mm cable, with the termination resistor enabled on the last module. Enough for a basement panel and lines across the whole building.

Does the system connect to Home Assistant?

Yes, through the eWeLink integration — SONOFF's SPM documentation mentions it directly. Day-to-day control and charts live in the eWeLink app, including LAN mode on the same network as the router.

What happens to the lines after a blackout?

Power-on behaviour is set per channel: on, off or last state. A tenant's fridge comes back on its own, while a workshop machine safely waits for a manual start.

Can I pull readings into my own billing system?

Yes. SPM has an official DIY mode with an HTTP API: channel readings and control are available over REST — the manufacturer documents the SPM-Main HTTP API separately, used for billing in Node-RED or spreadsheets.

Sonoff SPM-4Relay — 4-relay power meter, Moldova

Name: Sonoff SPM-4Relay stackable power meter module with 4 relays 20 A
Brand: Sonoff
SKU: SONOFF-SPM-4RELAY
Price: 1699 MDL
Availability: InStock

casasmart.md

Compatibility

Works with these ecosystems

Ecosystems

eWeLink
Home Assistant

What it is, who it's for, what it does

About this product

Numbers end arguments: when every circuit in the panel has its own meter, nobody guesses who heated the water. SPM-4Relay splits loads across four isolated relay channels rated 20 A each (up to 80 A per module) and tracks current, voltage, power and kWh per line in the eWeLink app.<br><br>It is an expansion module: it connects to the SPM-Main head unit over a shielded RS-485 bus and will not start without it. The upside is growth — up to 32 modules and 128 channels on one SPM-Main. Each channel gets its own schedules, OPS protection thresholds and power-on behaviour, and an overloaded line is switched off automatically.

Delivery
Free from 1500 MDL
Returns
30 days to return
Warranty
24 months

15+projects delivered300+devices installed3 yearslocal-first experienceChișinăushowroom Columna 153Book a showroom visit →

CasaSmart essentials

What it works with, what it needs, what you can do

Verified compatibility

We test every device for these ecosystems. For non-standard integrations contact us before ordering.

Home Assistant
Zigbee
Matter
KNX
Wi-Fi

Install & requirements

What you need on your side and what we deliver.

Zigbee hub or Matter gateway for wireless variants
65 mm back-box or DIN panel for wired variants
Local setup on Home Assistant — included in install

Request install quote

Smart scenarios

Three typical automations we set up after the install.

01Morning: warm light + blinds up + climate at 22 °C
02Leaving: lights off, arm sensors, close the gas
03Evening: warm ambient + cinema scene

Where it works

Use cases

Home

In a Chișinău guesthouse every room sits on its own channel: at month end the owner exports per-line kWh and splits the bill without arguments.

Home

Four machines, four 20 A lines: OPS trips only the overloaded line after a set delay while the others keep running, with each machine's usage in eWeLink.

Home

The shop added a warehouse and a coffee corner — more modules joined the SPM-Main: up to 32 SPM-4Relay units and 128 channels in one system.

For the installer

Technical specifications

full spec · wiring · datasheet

Power

Input/output: 100–240 V~, 50/60 Hz
Max. current per channel: 20 A
Max. total module current: 80 A

Other

Channels: 4 isolated, relay and metering on each
Measurements per channel: current, voltage, power, kWh
OPS protection: min./max. power, voltage, current, shutdown delay
Data storage (in SPM-Main): microSD SDHC 8–32GB, over 20 years of statistics
Included: RVVSP cable 50 cm, instructions

Connectivity

Connection to SPM-Main: RS-485, RVVSP 2×0.2 mm cable, bus up to 100 m
Zoom: up to 32 SPM-4Relay modules (128 channels) per one SPM-Main

Wireless

Network (via SPM-Main): Wi-Fi IEEE 802.11 b/g/n 2.4 GHz or Ethernet

Physical

Mounting: DIN rail, distribution board
Dimensions (W×H×D): 250 × 90 × 66,5 mm
Housing: PC V0, white

Environment

Operating temperature: −10…+40 °C

Full device datasheet

Support

Frequently asked questions

Does the SPM-4Relay work without the SPM-Main?
No. It is an expansion module on the RS-485 bus: the manufacturer states the Main and 4-Relay must be used together. The SPM-Main handles the Wi-Fi or Ethernet link and supports up to 32 modules.
Why doesn't the module come online even though the bus is wired?
Usually channel 1 has no power: per the manufacturer's wiring diagram, the L1/N1 input feeds the module itself. Energise channel 1, then check RS-485 polarity and the termination resistor on the last module.
How do I see per-line consumption and for what period?
In eWeLink each of the four channels shows current, voltage, power and kWh history; operation logs are kept for three months. The SPM-Main additionally writes statistics to microSD (8–32 GB) — over 20 years of data per the manufacturer, with reports exported from the card.
I already have breakers in the panel — what are OPS thresholds for?
A breaker protects the wiring from shorts and fault overloads, while OPS solves the business side: a power cap per tenant, delayed cut-off, minimum power as a fault alarm. The manufacturer explicitly warns that OPS is not a substitute for a circuit breaker.
How many modules can I add and over what distance?
Up to 32 SPM-4Relay modules per SPM-Main — 128 channels. The RS-485 bus runs up to 100 m over shielded RVVSP 2×0.2 mm cable, with the termination resistor enabled on the last module. Enough for a basement panel and lines across the whole building.
Does the system connect to Home Assistant?
Yes, through the eWeLink integration — SONOFF's SPM documentation mentions it directly. Day-to-day control and charts live in the eWeLink app, including LAN mode on the same network as the router.
What happens to the lines after a blackout?
Power-on behaviour is set per channel: on, off or last state. A tenant's fridge comes back on its own, while a workshop machine safely waits for a manual start.
Can I pull readings into my own billing system?
Yes. SPM has an official DIY mode with an HTTP API: channel readings and control are available over REST — the manufacturer documents the SPM-Main HTTP API separately, used for billing in Node-RED or spreadsheets.

Same ecosystem

Works together

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Questions about this product?

A CasaSmart manager calls you within 1–2 working hours and answers anything — compatibility, install, alternatives.

+373 60 944 922

Updated: 13 June 2026· reviewed by CasaSmart Expert Team

Compatibility