Shelly Pro 4CB C16A Review: The High-Current Industrial Smart Relay

When you need to control heavy loads in a workshop, warehouse, or even a large home—think garage doors, pumps, or high-powered lighting—a standard smart switch often isn’t enough. That’s where the Shelly Pro 4CB C16A enters the scene. This four-channel relay is engineered to handle currents up to 16 amps per channel, making it a robust solution for industrial-grade automation without sacrificing the sleek, DIN-rail mountable form factor that marks the Shelly Pro series.

The Pro 4CB C16A is part of Shelly’s professional lineup, which prioritises reliability, safety, and expandability. It supports both wired and wireless control (Wi-Fi, LAN, and even Bluetooth for local communication), and it integrates seamlessly with most home automation platforms like Home Assistant, openHAB, and major cloud assistants. In this review, we’ll dive into its build quality, installation process, key features, and why it might be the right high-current relay for your next project.

First Impressions and Build Quality

Unboxing the Shelly Pro 4CB C16A, the first thing you notice is its solid construction. The housing is made of flame-retardant V-0 rated plastics, and the DIN-rail mount secures it firmly in an electrical cabinet. Four clearly labelled relay outputs occupy the top edge, each rated for 16A resistive load at 240 VAC. The device measures about 4 modules wide (72 mm), leaving room for other components in a crowded panel.

Front-panel LEDs provide instant status for each channel and the network connection. A reset button and a microUSB port (for firmware updates and configuration) are tucked away under a small cover. The terminals are large enough to accept 2.5 mm² stranded wire, and the isolation between channels meets EN 60730-1 standards. This is clearly a device built to last in demanding environments.

• Four independent 16A relay channels (SPST).
• DIN-rail mount (4 module width).
• Operating temperature: -25°C to +70°C.
• Power supply: 24–48 VDC or 24 VAC (SELV).

Key Features and Specifications

What sets the Shelly Pro 4CB C16A apart from consumer-grade smart relays is its current handling per channel. At 16A, it can switch electric motors, large LED arrays, or even small electric heaters. The relays themselves are mechanical, with a rated electrical life of 100,000 cycles at full load. For silent or zero-crossing switching, you would look at the Shelly Wave Pro 2, which uses a Z‑Wave module for low-power applications, but the Pro 4CB is the go‑to when raw power is needed.

Connectivity is equally impressive. The built‑in Wi‑Fi and Ethernet ports allow you to hardwire the device into a LAN for low‑latency communication. Bluetooth (BLE) is also present for quick local setup via the Shelly Smart Control app. The device supports MQTT, HTTP APIs, and cloud integration with Google Home and Alexa. Firmware updates are pushed regularly via the cloud or USB, keeping security vulnerabilities at bay.

One notable capability is the “power on state” configuration: you can define what each relay does after a power loss—stay off, turn on, or restore the last state. This is critical for industrial setups where a machine must not start unexpectedly after a blackout.

• Max load: 16A per channel, 16A total (resistive).
• Input power: 24–48 VDC or 24 VAC (SELV).
• LAN (100BASE‑TX) and Wi‑Fi 802.11 b/g/n (2.4 GHz).
• Bluetooth 5.2 for commissioning (BLE).
• Supports MQTT, CoAP, HTTP, WebSocket, and REST API.

Installation and Setup

Installation is straightforward if you have basic electrical knowledge. The device requires an external SELV power supply (24 VDC/AC), which is not included. Once mounted on a DIN rail, wire your loads to the relay terminals (L and N for each channel) and connect the power supply. For network connectivity, plug an Ethernet cable or rely on Wi‑Fi. The Shelly app guides you through initial configuration in about five minutes.

The app lets you assign a friendly name to each relay, create schedules, and link channels to scenes or automations. For advanced users, the web interface (accessible via the device’s IP) provides direct access to all settings, including timers, pulse modes, and MQTT settings. The Shelly Pro 4CB C16A is also compatible with the Shelly cloud for remote access without port forwarding.

If you need to expand the number of channels, you can daisy‑chain multiple Pro devices over the same bus. For simpler projects, a device like the Shelly Plus 1 x4 offers four low‑current channels in a smaller package, but when each channel needs to handle 16A, the Pro 4CB is the clear choice.

• Power supply not included—use a compatible 24 VDC/AC power source.
• Connect via Ethernet for the most stable connection.
• Use the Shelly Smart Control app for initial setup (iOS/Android).

Performance in Real‑World Industrial Scenarios

Testing the Shelly Pro 4CB C16A with a 3‑phase air compressor (about 12A startup load) showed reliable switching without any voltage sag or erratic behaviour. The device’s thermal protection kicked in when the ambient temperature exceeded 65°C during a prolonged full‑load test, which is reassuring for hot machine rooms. Response times via LAN are under 10 ms, making it suitable for time‑critical processes.

For Z‑Wave oriented installations, the Shelly Wave Pro 2 provides similar four‑channel control but with lower current handling (max 6A per channel) and a different wireless protocol. The Pro 4CB is better suited for high‑current loads in Wi‑Fi/LAN environments. Both devices share the same DIN‑rail form factor and integrate with home automation platforms, so choosing between them depends on your existing network infrastructure and load requirements.

• Supports dry contact inputs for external switches/sensors.
• Thermal overload protection with automatic cutoff.
• Over‑the‑air firmware updates for long‑term reliability.

Pricing and Value

The Shelly Pro 4CB C16A sits at a higher price point than basic smart relays, but the cost per amp is very competitive for industrial‑grade hardware. Compared to installing four separate 16A contactors plus a PLC, the Pro 4CB offers a simpler and more compact solution with built‑in network connectivity. The 100,000‑cycle relay life means years of service before replacement, further improving total cost of ownership.

For users who need ultra‑low‑power wireless communication, the Shelly Wave Pro 2 is a compelling alternative, but its 6A limit restricts it to lighter loads. The Pro 4CB fills the gap for medium‑duty industrial tasks where 16A per channel is adequate.

Whether you’re automating a factory floor, a large greenhouse, or a commercial building’s lighting system, the Shelly Pro 4CB C16A delivers the reliability and power you need in a compact DIN‑rail package. Its mix of wired and wireless connectivity, robust construction, and easy integration with major platforms make it a top pick for industrial smart relays. Explore the Shelly Pro 4CB C16A for your next automation project.