Shelly Plus 1PM vs Pro 2CB: Which Energy Monitoring Relay Should You Choose?

When you’re building a smart home or office, monitoring energy consumption is a key step toward efficiency and savings. Shelly offers a range of relays with built-in power metering, and two of the most popular are the Shelly Plus 1PM and the Shelly Pro 2CB. Both deliver real-time energy data, but they differ in relay count, form factor, and ideal use cases.

In this buying guide, we’ll break down the differences between these two energy monitoring relays—focusing on single versus dual relay design, monitoring accuracy, load handling, and integration options. By the end, you’ll know exactly which model fits your needs. Along the way, we’ll also mention complementary Shelly products like the Shelly 1 Mini Gen3 and Shelly Plug M Gen3 White 4-pack to help you expand your smart energy setup.

At a Glance: Shelly Plus 1PM vs Shelly Pro 2CB

The Shelly Plus 1PM is a single-relay WiFi device with energy monitoring, designed for retrofitting into wall boxes or enclosures where space is tight. It handles up to 16A and includes advanced metering features like active power, apparent power, and energy counters. The Shelly Pro 2CB, on the other hand, is a DIN-rail mounted dual-relay controller with two independent channels, each with its own energy monitoring. It’s built for electrical panels and professional installations, supporting up to 20A per channel.

While both devices measure power with high accuracy, the Pro 2CB adds Ethernet connectivity and a built-in web interface for direct configuration—ideal for commercial or industrial environments. The Plus 1PM relies solely on WiFi and Bluetooth for setup and communication, making it more suited for residential retrofits.

• If you need a compact, single-relay monitor for a specific appliance, the Plus 1PM is a cost-effective choice.
• If you require two independent channels with higher current capacity and wired networking, the Pro 2CB is the professional option.

Design and Installation: Compact vs DIN-Rail

Installation environment is a major deciding factor. The Shelly Plus 1PM is extremely compact—it fits behind existing switches and outlets, making it perfect for hidden retrofits. It can be placed in a standard wall box alongside other devices. For those with limited space, the Shelly 1 Mini Gen3 offers an even smaller footprint, though without energy monitoring. The Plus 1PM strikes a balance between size and functionality.

The Shelly Pro 2CB is designed for DIN-rail mounting inside a distribution board. It’s larger but offers more robust connections and an integrated power supply. This makes it ideal for new constructions or major renovations where you can plan the electrical panel layout. The Pro 2CB also has a clear status display and physical buttons, simplifying on-site commissioning.

Single vs Dual Relay: Choosing the Right Number of Channels

The core difference lies in relay count. The Plus 1PM has one relay, so it monitors and controls a single circuit. Use it for a washing machine, water heater, or a dedicated lighting circuit. If you need to monitor two separate loads, you would install two Plus 1PM units. The Pro 2CB, with its two independent relays, can handle two different loads from one device—saving space in the panel and reducing wiring complexity.

For plug-level monitoring, consider the Shelly Plug M Gen3 White 4-pack, which gives you four WiFi smart plugs with energy tracking. While not a relay, it’s an excellent way to monitor individual appliances without any wiring. The Plus 1PM and Pro 2CB, however, are hardwired solutions for fixed installations.

• Single relay (Plus 1PM): Ideal for retrofitting one high-usage appliance or circuit.
• Dual relay (Pro 2CB): Best when you want to monitor two separate circuits (e.g., lighting + outlets) from one device in the panel.

Energy Monitoring Features: Accuracy and Data

Both relays provide real-time energy monitoring with high accuracy, but the data granularity differs slightly. The Plus 1PM measures active power (W), energy (kWh), current (A), and voltage (V) every second via WiFi. It also supports power on/off logging. The Pro 2CB offers similar metrics for each channel independently, and because it stays connected via Ethernet, data streaming is more stable in environments with heavy WiFi congestion.

Both devices integrate seamlessly with Home Assistant and mqtt, giving you dashboards and automation triggers based on power thresholds. For lighting control, you might pair these relays with a smart bulb like the Shelly Duo Bulb E27 Gen3 to dim and monitor simultaneously—though the relay controls the circuit, and the bulb has its own smart features.

Load Capacity: How Much Can Each Handle?

Understanding load limits is critical. The Shelly Plus 1PM handles up to 16A at 230V AC (3680W), which covers most household appliances like refrigerators, pumps, and electric heaters. The Shelly Pro 2CB supports up to 20A per channel (4600W), making it suitable for heavier loads such as large air conditioners or industrial machines. Additionally, the Pro 2CB has a total maximum current that must be respected across both channels.

For resistive loads (heating) and inductive loads (motors), both relays include over-temperature and overcurrent protection. If you need to control and monitor a dimmable lighting circuit, the Shelly Dimmer2 is a better choice than a relay, as relays only switch on/off, not dim.

• Plus 1PM: 16A max, great for single high-power appliances.
• Pro 2CB: 20A per channel, ideal for dual heavy loads in a panel.

Smart Home Integration and Automation

Both devices work with Shelly Cloud app, Google Home, Alexa, and are compatible with over 30 third-party platforms. The Plus 1PM uses WiFi and BLE, so it’s quick to pair via app. The Pro 2CB adds Ethernet, which is a huge advantage for installations where WiFi is unreliable or where you want a dedicated network connection. It also supports KNXnet IP via a separate gateway, extending its use in commercial buildings.

Automation scenarios: Use the Plus 1PM to turn off a water heater when power exceeds a threshold, or use the Pro 2CB to stagger two high-power loads to avoid tripping a breaker. For wireless control without hardwiring, the Shelly BLU Button1 Blue can trigger these relays via Bluetooth, adding a convenient remote switch.

Which One Should You Buy? Decision Guide

Choose the Shelly Plus 1PM if you’re retrofitting an existing switch box, need one channel, and prefer a low-profile solution. It’s great for homeowners who want to monitor a specific circuit without changing the electrical panel. If you plan to expand, you can add more Plus 1PM units as needed.

Choose the Shelly Pro 2CB if you’re doing a new installation or panel upgrade, need two channels with high current capacity, and want a wired connection for reliability. It’s the professional’s choice for commercial spaces, workshops, or whole-house energy management systems. Both are excellent for energy monitoring—your main decision is based on relay count, installation space, and networking preferences.

• Need a single relay behind a wall switch? Go with Plus 1PM.
• Need two relays in the panel with Ethernet? Choose Pro 2CB.

Whether you opt for the compact Shelly Plus 1PM or the dual-channel Shelly Pro 2CB, you’ll gain accurate energy monitoring and reliable control. Evaluate your current load requirements, available installation space, and preferred connectivity. For those starting with a single appliance, the Shelly Plug M Gen3 White 4-pack is another excellent entry point for wireless energy tracking with no wiring needed. Explore these smart relays and power monitoring solutions at Shelly Europe to take the next step toward an energy-efficient smart home.