[Connect up to 32 SPM-4Relays]One SPM-Main can be connected 32 SPM-4Relays. Each SPM-4Relay has 4 isolated channels to help you manage devices more conveniently. [Power metering]You can monitor the power consumption by checking eWeLink App on your mobile phone. Obtaining current, voltage and power easily. [Max. 20A/Gang]Each channel can support maximum current of 20A, no fear of high power load. [Communicated by RS-485]The SPM-Main communicates with the SPM-4Relays through RS-485, which allows for multi-terminal and stable long-distance data transmission. [Overload Protection]Once the overload protection is enabled, it can protect your devices from burning out.