There's a situation that comes up in any electrical refurbishment: the customer wants to monitor their three-phase consumption, but when you open the panel there's no room for three 120 A clamps. They're bulky and in a panel that has grown over the years, they simply don't fit.
The Shelly Pro 3EM-3CT63 exists precisely for that.
One piece instead of three
The 3CT63 integrates the three phases into a single 14×54×26 mm piece that mounts directly over the circuit breaker, with no rail fixing and taking up no extra space.
That's its real selling point: no other three-phase meter in the range solves the space problem this way. In exchange you accept two limits: 63 A maximum and a conductor opening of 9 mm.
Where it makes the most sense
Shelly's documentation aims it at environments where panel space is a scarce resource:
- Refurbishments and panel expansions. When you need to add metering to an existing installation without rebuilding it.
- Commercial buildings and offices. Floor panels with little margin.
- Motor control centers. Monitoring currents per machine, useful for preventive maintenance.
- Data centers. Precise per-circuit metering in very dense cabinets.
- Substations and industrial installations. Where space is always at a premium.
Integration via Modbus TCP
Like the rest of the Pro range meters, this unit speaks Modbus TCP over port 502, in addition to MQTT and RPC.
Modbus is the standard protocol of industrial automation and building management systems. Being able to speak it natively avoids intermediate gateways and greatly simplifies integration into installations that already have a BMS or SCADA running.
The Pro EM-50, the Pro 3EM and the Pro 3EM-400A share this capability. If your project needs Modbus but you have no space problem, any of them works: the choice then goes back to maximum current and clamp size.
Connectivity via Wi-Fi, Ethernet and Bluetooth 4.2, with TLS on incoming connections.
What data it delivers
4-quadrant measurement per phase: active and apparent power, active and apparent energy, power factor and fundamental active and reactive energy. Accuracy of 1% between 2 and 63 A.
It stores up to 60 days at one-minute resolution (more than the Pro 3EM, which gives 45), exportable to CSV and JSON.
It supports both three-phase and single-phase wiring, which makes it more versatile than its name suggests.
Check this before you order it
The 9 mm opening is the limitation that causes the most returns. Measure the outer diameter of the cable with its insulation, not the cross-section in mm²: they're different things and the whole cable passes through the opening.
And if you're going to control loads, bear in mind it has no relay: you need the Shelly Pro 3EM Switch Add-on.
Related products and guides
- Shelly Pro 3EM-3CT63: the meter with the 63 A combined clamp.
- Shelly Pro 3EM: if you exceed 63 A or 9 mm.
- Pro 3EM-3CT63 installation guide.
- Pro 3EM-3CT63 frequently asked questions.
- Pro range comparison: the four DIN-rail meters.
Not sure if your cables fit through the opening? Send us a photo of your panel and we'll confirm it. Technical support in English and shipping from Spain.
