SPM-Main & SPM-4Relay

Product Overview

Introduction

Product Name	SONOFF Smart Stackable Power Meter (Main Unit)
Product Model	SPM-Main

Product Name	SONOFF Smart Stackable Power Meter (4-Relays)
Product Model	SPM-4Relay

SONOFF SPM is a smart, stackable power monitoring system that can control up to 128 channels by connecting to 32 SPM-4Relays. Each channel handles up to 20A, perfect for managing high-power devices. Real-time monitoring of current, voltage, and power is available in the eWeLink app. With microSD storage for over 20 years of data logging and built-in overload protection, it’s ideal for secure, organized energy management.

Notice:

The SPM-Main and SPM-4Relay must be used together for proper operation. One SPM-Main can support up to 32 SPM-4Relay units.

Highlights

UP to 32 SPM-4Relays
One SPM-Main connects up to 32 SPM-4Relays. Each relay includes 4 isolated channels for organized and scalable device control.
20A per Channel
Each channel supports up to 20 amps, making it ideal for high-power devices.
Overload Protection
Automatically cuts off power during overloads to protect your devices and ensure system safety.
MicroSD Storage
Store over 20 years of power data and up to 20,000 operation logs per device. Quickly export consumption reports via SD card.
Power Monitoring
Track real-time current, voltage, and power usage through the eWeLink app for smarter energy management.

Applications

Commercial/Industrial – Ideal for energy monitoring and control in server rooms, offices, retail stores, or workshops.
Residential Projects – Manage and track multiple high-current circuits (e.g., EV chargers, HVAC zones, workshop equipment).
Centralized Control Cabinets – DIN‑rail mountable design fits electrical panels for clean, organized installations.
Automation & API Integration – Use eWeLink or DIY REST/Node‑RED workflows for real‑time monitoring and control of individual channels.

Specification

SPM-Main

Model	SPM-Main
Input	100-240V ~50/60Hz 50mA Max
Wi-Fi	IEEE 802.11 b/g/n 2.4GHz
Working Temperature	-10℃~+40℃
App Operating Systems	Android & iOS
Shell Material	PC V0
Dimension	142.5x90x66.5mm

SPM-4Relay

Model	SPM-4Relay
Input	100-240V ~50/60Hz 20A/Gang 80A/Total Max
Output	100-240V ~50/60Hz 20A/Gang 80A/Total Max
Working Temperature	-10℃~+40℃
Shell Material	PC V0
Dimension	250x90x66.5mm

Key Features

eWeLink Platform

SPM-Main

Device Home Page Functions
Key Features	Feature Description
SPM-4Realy list	View the list of SPM-4Relay connected to the SPM-Main.
Scan device	Scan for connected SPM-4Relay. If not yet added, they will be added during this process.

Device Settings
Key Features		Feature Description
Share		The device can be shared with other eweLink accounts.
LAN control		A control method where the app communicates directly with the device over the same router, without going through the cloud platform. On/Off
Network Indicator		On/Off
Delete Device		Remove the device from the eWeLink platform.

SPM-4Relay

Device Home Page Functions
Key Features	Feature Description
On / Off	Device on/off state
Consumption	Real-time monitoring or historical record of power parameter changes on Channel 1 to Channel 4.
Schedule	Set the device to complete the specified action at the specified time.
Find me	Helps locate the corresponding device in the electrical cabinet.

Device Settings
Key Features		Feature Description
Assign location		Set up the home and room where the device is located.
OPS		Once the predefined threshold is exceeded, the associated load channel is turned off for safety. Channel 1~4: Min power/Max voltage/Min voltage/Max current/Max power Delay to switch off
Smart Scene	Trigger Condition	Channel 1~4 On/Off
	Execution Action	Channel 1~4 On/Off
Push notifications		After turning on "Push notifications", also make sure to grant notification permissions in Phone Settings > Permissions for the eWeLink app. This allows you to receive push notifications when the device status changes. On/Off
Logs		Records of device status changes. (You can view the operation records of the past three months)
Power-on State		The switch state of the device when power is restored after a power outage. Channel 1~4: On/Off/Last State
Delete Device		Remove the device from the eWeLink platform.

Installation and Configuration Guide

SPM-Main

LED indicator (Blue)

LED indicator status	Description
Quick flash	In Pairing Mode
Keeps on	Online
Flashes once	Unable to discover the router
Flashes twice	Connect to the router but fail to connect to server
Flashes three times	OTA

LED indicator (Another color)

LED Indicator (Another color)	Description
Green once	Read or write SD card
Orange	The device is malfunctioning and not working properly

Pairing button

Button	Description
Press & hold 5 seconds	Device enters the pairing mode.
Click	Scan for connected SPM-4Relay. If not yet added, they will be added during this process.

SPM-4Relay

Front

Bottom

Signal indicator

Signal indicator	Description
Infinitive flashes	After being added to SPM-Main, it will communicate with the Main every 1~2 seconds and flash a prompt.

ON/OFF LED indicator

Signal indicator	Description
Keeps on	Device is on
Keeps off	Device is off

Wiring Instruction

WARNING:

Please install and maintain the device by a professional electrician. To avoid an electric shock hazard, do not operate any connection or contact the terminal connector while the device is powered on!

Wiring Instruction of SPM-Main & SPM-4Relay and SPM-4Relay & the Slave Unit

The main unit can be added up to 32 slave units (The length of the RS-485 bus shall be less than 100m)
The wire connected to the main unit and slave unit must be a 2-core RVVSP cable with a single wire diameter of 0.2mm.
To ensure the reliable communication of the RS-485 bus, please keep one end of the shielded layer connected to the ground wire and the other end hanging in the air.

Light Fixture Wiring Instruction

There are 4 channels in SPM-4Relay, the first channel is designed to power the device so that it has to be powered on; Each channel is independent, only the input end is powered on can the corresponding output end of the channel work successfully.
Ensure the proper wiring before powering the units on.

Terminals		Wires
L	The SPM-Main Live (Input Terminal)	L	Live (100~240V) Wire
N	The SPM-Main Neutral (Input Terminal)	N	Neutral Wire
L1 ~ L4	The SPM-4Relay Live (Input Terminal)
L1 Out ~ L4 Out	The SPM-4Relay Live (Output Terminal)
N1~ N4	The SPM-4Relay Neutral (Input Terminal)
N1 Out ~ N4 Out	The SPM-4Relay Neutral (Output Terminal)

Special Reminder

The "RS-485 Termination Resistor Switch" of the slave unit is off by default. To make sure stable communication, the "RS-485 Termination Resistor Switch" of the terminal slave unit shall be turned on.

Add Device

eWeLink Platform

Open eWeLink, tap "+” and select "Add Device", then follow the prompt on the App.

Notice：

It's required to turn on the Bluetooth on your Phone when adding a device.

Add the Slave Unit to the Main Unit

Press the Pairing Button on the main unit once to enable it to enter the scan status, then the COMM Indicator of the slave unit“flashes slowly”. The slave unit will appear in the list of main unit interface on the eWeLink App as a sub-device after being added to the main unit.

Notice:

The slave unit has not been scanned successfully within 20s, the main unit will exit the scan status. If you want to scan the slave unit again, you can press the Pairing Button on the main unit once again.
The connected slave unit can be added and controlled by powering on the main unit again.

Insert Micro SD Card (SPM-Main)

Make sure Micro SD Card is inserted correctly (Micro SD Card is sold separately).

FAQ

1. What are the maximum capacities and scalability of the system?

Up to 128 channels supported (one SPM-MAIN + 32 SPM-4RELAY modules × 4 channels each)

2. How to use DIY mode?

DIY mode allows you to call the API interface to control SPM. For an introduction to DIY mode, see:

https://sonoff.tech/sonoff-diy-developer-documentation-spm-main-http-api/

3. What kind of overload protection and safety mechanisms are included?

The SPM system supports configurable overload protection with adjustable thresholds and delay settings. It can shut off or alert when a channel exceeds safe current, voltage, or power limits. However, it is not a substitute for a proper circuit breaker and should not be used as a safety fuse.