What is the Shelly i3

11 Jul 2021

The Shelly i3 is not like other Shelly products. It doesn’t have a relay so it can’t physically control a circuit or be used as a switch. It can however monitor and show the status of up to 3 inputs such as switches and sensors and command other connected Shelly relays, sensors, or HTTP, MQTT or CoAP controlled devices.

Thanks to having no relays or dimmer circuits, the Shelly i3 is a very small device, measuring just 40mm x 36mm x 10mm. It can easily fit into a crowded junction box or switch backbox where there may not be enough room for the larger devices with relays built in.

To help keep its small form, the Shelly i3 comes with wires built directly into the device, instead of the typical terminal blocks seen in the other Shelly devices. There are 5 colour coded wires coming from the i3 for connections to Live (L) in red, Neutral (N) in Blue, Input 1 (I1) Black, Input 2 (I2) Black and Input 3 (I3) Black.

Shelly i3 Installation

Why would you use a Shelly i3?

The Shelly i3 is ideal for sending commands based on the state of a switch. The best way is to achieve this is within a standard UK lighting circuit would be to detach the light switch from it’s circuit. This would mean at the junction box you would connect the Shelly i3 to switched live coming from the switch while using the lighting circuit live and neutral to power the device itself. The light itself would be switched from a Shelly Relay, not connected to the switch itself, or even Smart Bulbs being permanently powered on. The switch is then used to control the i3 to send commands to Shelly Cloud or to a home automation system such as Home Assistant to perform an action such as a scene or simply turn the lights on somewhere else.

Like all Shelly devices, it works in a wide range power supply both in AC, 110-230V ±10%, 50/60Hz and DC, 24 – 60V. This means it lends itself to several different applications as long as they are wired on the same circuit using the same power supply. We have seen the Shelly i3 used with wired motion sensors, reed switches such as door sensors, toggle switches and momentary switches.

To get the full benefit of all of the 24 different possible actions Shelly offer with the i3, you are best to use a momentary type of switch which gives you the most range of commands including short press and long press options. The i3 also works with normal rocker style switches but they are only able to support simple on and off commands.

The Shelly i3 has 3 channels which means it can have up to 3 different inputs attached to it from the same circuit, such as 3 different switches on the same lighting circuit. The i3 works by detecting the state of the light switch on the circuit while having no actual effect on that circuit. It then sends the state of that switch via the Shelly Cloud, HTTP, MQTT or CoAP to trigger an action somewhere else. 

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