The Sonoff SPM-4Relay is a smart power meter expansion module designed to increase the monitoring and control capabilities of your electrical system. By connecting to an SPM-Main unit via RS485, this module adds four independent channels to your setup, each supporting a maximum current of 20A for a total capacity of 80A. It operates within a voltage range of 100-240V AC at 50/60Hz, allowing you to track voltage, current, power, and energy consumption for each circuit in real time through the eWeLink app. Built for stability and safety, the device is housed in a white PC V0 fireproof plastic casing and measures 250 x 90 x 66.5 mm, making it easy to install on a standard DIN rail. To ensure your data is preserved even during connectivity gaps, it includes a microSD card slot that supports storage from 8GB to 32GB. This system is highly scalable, as you can link up to 32 of these modules to a single main unit to manage as many as 128 channels, providing a comprehensive solution for those who need detailed energy oversight and individual circuit control with built-in overload protection.