Shelly
Bulgarian WiFi IoT relays — rapid retrofit solution bridged to KNX via Home Assistant local API.
Shelly (Allterco Robotics, Sofia, Bulgaria — founded 2016) manufactures compact WiFi-based smart relays, dimmers, sensors, and energy metering devices designed for installation inside existing switch boxes and distribution boards. In KNX building automation projects, Shelly devices fill a specific niche: cost-effective retrofit of circuits where running new KNX TP bus cable is impractical or economically unjustifiable — for example, individual circuits in an existing apartment renovation, AV rack control in a small office, or holiday home lighting automation. The integration architecture is always the same: Shelly device communicates locally via CoAP (Gen1) or MQTT (Gen2/Gen3) to Home Assistant, which runs the KNX integration and bridges state changes between Shelly group addresses and KNX group addresses in both directions. Shelly is not a professional KNX product — it is not certified to IEC 61439, has no ETS6 plugin, and is not suitable for safety-critical circuits — but Shelly Gen2 devices configured for local-only MQTT with no cloud dependency provide adequate reliability for residential and light commercial low-criticality loads.
Role in our panels
How we use Shelly
Shelly Gen2 and Gen3 devices (Plus series, Pro series) use a documented local REST API and MQTT protocol that allows full control and status readback without any cloud service dependency — a critical requirement for KNX integration, where cloud outages cannot disrupt building control. The integration flow for relay bridging: Shelly Plus 1PM publishes relay state to a local Mosquitto MQTT broker running on Home Assistant or Synology NAS; HA subscribes to the MQTT topic and updates the entity state; HA KNX integration writes the entity state as a binary value (DPT 1.001) to a KNX group address, and conversely a KNX binary 1 written by a KNX push-button can trigger a Shelly relay via HA. For energy monitoring: Shelly EM Gen2 with 3-phase CT clamps publishes kW and kWh values per phase to MQTT; HA reads these and writes to KNX group addresses for visualization on a KNX energy display or Gira X1 dashboard. The Shelly Pro DIN-rail series (Pro 4PM, Pro 3EM) is the preferred choice for panel-mounted installations — standard 35mm DIN-rail form factor with screw terminals, unlike the compact retrofit models that use push-in connectors and rely on spring tension.
In PanelCraft panels for hybrid Shelly-KNX projects, only the Shelly Pro series is panel-mountable on DIN-rail — the Plus series sits inside wall boxes, not in the panel. Panel design for Shelly-KNX projects includes: Shelly Pro 4PM on DIN-rail (4× relay, power metering); Shelly EM Gen2 on DIN-rail adjacent to the main incomer for 3-phase CT metering; a dedicated IoT VLAN on the managed switch (separate from the KNX IP subnet) with firewall rules isolating Shelly devices — this is important because Shelly firmware updates pull from Shelly cloud servers, and the IoT VLAN prevents firmware traffic from reaching the KNX network. The local Mosquitto MQTT broker runs on the HA instance (or Synology); the HA KNX integration connects to the KNX IP router (Weinzierl 730, MDT IP Interface) on the KNX IP VLAN. No Shelly device has direct KNX TP bus connection — all bridging is done by HA automation rules mapping MQTT topics to KNX group addresses and vice versa.
Used in these project types
Shelly products
Key components we install
Shelly Plus 1PM Single Relay with Power Metering
1-channel 16A relay with integrated 50Hz power metering (W, kWh). WiFi Gen2 with local CoAP and MQTT API. Fits behind a standard EU 60mm switch faceplate (45×41×17mm). For retrofit: replaces traditional switch mechanism; Shelly publishes relay state and power consumption to HA MQTT; HA bridges to KNX binary group address. No cloud required for local MQTT operation. Not DIN-rail mountable — install inside wall box or junction box.
Shelly Plus 2PM Dual Relay or Roller Shutter
2-channel relay (10A per channel) with roller shutter mode for motor control. In roller shutter mode, drives a single AC motor with up/down direction control. For retrofit roller blinds or venetian blinds: HA bridges shutter position (0-100%) from KNX DPT 5.001 shutter group address to Shelly 2PM open/stop/close MQTT commands. Also usable as 2× independent relay for two lighting circuits. Energy monitoring per channel.
Shelly Dimmer 0/1-10V Analog Output
0-10V DC analog output for controlling LED drivers, DALI drivers with 0-10V input, or Belimo actuators with 2-10V control. Push-button input for local manual override. WiFi Gen2 MQTT. HA translates KNX DPT 5.001 (0-255 integer) to Shelly brightness percentage (0-100%), which the device converts to 0-10V output. Eliminates need for a KNX analog output module (e.g. MDT AMS-0816.02) for non-KNX 0-10V loads in retrofit projects.
Shelly Pro 4PM DIN-Rail 4-Channel Relay
DIN-rail mountable 4-channel relay, 16A per channel, with power metering. RJ45 Ethernet port (100Mbps) plus WiFi Gen2. For panel-mounted installations: 4 circuits controllable via local MQTT or Ethernet REST API. HA bridges all 4 relay states and power readings to KNX group addresses. Used in small office AV racks, server room power control, and kitchen appliance circuits in residential KNX projects. Screw terminal connections suitable for 2.5mm2 wire.
Shelly EM Gen2 3-Phase Energy Meter
3-phase energy meter with external CT clamps (50A, 120A, or 200A options). WiFi Gen2 MQTT. MID-certified version available for billing purposes. Modbus TCP option for direct integration without HA. For load management: EM Gen2 measures per-phase kW and cumulative kWh; HA reads via MQTT and writes to KNX group addresses (DPT 14.056 for active power, DPT 13.010 for energy counter) for display on KNX energy visualisation touch panel or Gira X1.
Shelly FAQ
Can Shelly devices and KNX coexist in the same building project?
Yes — the standard architecture uses Home Assistant as the integration hub, with Shelly devices on a dedicated IoT VLAN communicating via local MQTT to HA, and HA connecting to the KNX IP router (Weinzierl 730, MDT IP Interface) on the KNX IP subnet. HA automation rules map Shelly MQTT topics to KNX group addresses bidirectionally: when a Shelly relay changes state, HA writes the binary value to a KNX group address so that KNX visualization panels and loggers see the state; when a KNX push-button or timer writes to a KNX group address, HA receives the KNX telegram and publishes the corresponding MQTT command to the Shelly device. This coexistence is common in retrofit projects where main rooms have full KNX (MDT or Berker push-buttons, KNX HVAC) and secondary circuits (balcony lighting, boiler room, garden sockets) use Shelly Plus 1PM for cost reasons.
Is Shelly reliable enough for professional KNX installations?
Shelly Gen2 devices configured for local MQTT with cloud access disabled are reliable for low-criticality residential and light commercial loads — typical mean time between failures for the Pro series in temperature-controlled panels is comparable to budget-tier KNX actuators. However, Shelly is explicitly not suitable for safety-critical circuits: fire door holds, emergency lighting, evacuation alarms, and access control systems must use certified KNX devices that comply with IEC 62386 or IEC 14543. Shelly devices are also not certified to IEC 61439-1 for switchgear and controlgear assemblies, which is relevant if the panel must carry a CE mark under the Low Voltage Directive. For professional panel installations, use only the Shelly Pro DIN-rail series (Pro 4PM, Pro 3EM) with local-only MQTT and IoT VLAN isolation — the compact Plus series is a site-installed device, not a panel component.
How does Shelly Dimmer 0/1-10V work with KNX for non-KNX loads?
The Shelly Dimmer 0/1-10V outputs 0-10V DC on its output terminal and accepts a push-button input for local manual control. When integrated via HA, the KNX dimming group address (DPT 5.001, integer 0-255) is received by HA as a KNX telegram; HA maps the 0-255 integer to a 0-100% brightness value and publishes it to the Shelly MQTT topic; the Shelly device converts the brightness percentage to the corresponding 0-10V DC output voltage — 0% = 0V, 100% = 10V, 50% = 5V. This 0-10V output connects directly to the Y terminal of a Belimo air damper actuator or HVAC valve actuator, or to the DIM+ terminal of a non-KNX DALI driver with 0-10V analog input. The practical advantage is eliminating a KNX analog output module (such as MDT AMS-0816.02 at roughly 180 EUR) for a single non-KNX 0-10V load in a retrofit project — though for new installations with multiple 0-10V loads, the KNX analog module remains the preferred solution because it has ETS6 parameterization, does not require HA, and is panel-integrated.
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