It happens in every refit: the client wants to see their three-phase consumption, the panel is opened, and there is no room for three 120 A clamps. They are bulky, and in a panel that has grown over the years they simply do not fit. The Shelly Pro 3EM-3CT63 exists for that.
One piece instead of three
The 3CT63 covers all three phases in a single 14 × 54 × 26 mm piece that sits directly on the circuit breaker, with no rail fixing and no extra space taken. No other three-phase meter in the range solves the space problem this way.
The price is two limits: 63 A per phase and a 9 mm cable opening.
Where it makes sense
- Refits and extensions. Adding metering to an existing panel without rebuilding it.
- Offices and shops. Floor panels with little margin.
- Motor control centres. Current per machine, for preventive maintenance.
- Dense cabinets — data centres, industrial installations — where space is always short.
Modbus TCP, no gateway
Like the rest of the Pro range, it speaks Modbus TCP on port 502, alongside MQTT and RPC. Modbus is the protocol of industrial automation and building management systems; speaking it natively avoids intermediate gateways where a BMS or SCADA is already running.
It is not unique to this model: the Pro EM-50, the Pro 3EM and the Pro 3EM-400A speak it too. If you need Modbus but space is not a problem, any of them will do, and the choice comes back to current and clamp.
Wi-Fi, Ethernet and Bluetooth 4.2, with TLS on incoming connections.
What it reports
Four-quadrant metering per phase: active and apparent power, active and apparent energy, power factor and fundamental active and reactive energy, with 1% accuracy between 2 and 63 A.
It keeps up to 60 days at one-minute resolution — more than the Pro 3EM’s 45 — exportable to CSV and JSON, with a real-time clock. And it accepts single-phase wiring as well as three-phase.
Before you order it
The 9 mm is the limit behind most returns. Measure the outside diameter of the cable with its insulation, not the cross-section in mm²: they are different things, and the whole cable has to pass through the opening.
And if it is going to control loads, remember it has no relay: you need the Shelly Pro 3EM Switch Add-on. Past 63 A or 9 mm, the meter for the job is the Pro 3EM with its 120 A clamps.