Three-phase vs single-phase monitoring: choosing the right Shelly meter

Choosing between single-phase and three-phase energy monitoring is not a choice between a basic product and a more advanced one. The meter must match the electrical system being measured, the maximum expected current, the number of measurement points and the way the customer intends to use the data.

For a single-phase system requiring one or two current-transformer measurement points, Shelly EM Gen4 is generally the most flexible starting point. Shelly Pro EM-50 is designed for professional DIN-rail installations where two 50 A channels on the same phase, Ethernet connectivity and Modbus integration are required.

For a genuine three-phase supply, installers should start with the Shelly 3EM range. The choice between a 63 A, 120 A or 400 A model then depends on the current range, available panel space, communications requirements and whether the project needs whole-building monitoring or submetering. Supported Shelly 3EM models can also measure three independent single-phase circuits, making them useful for selected applications even where the incoming supply is not three-phase.

Which Shelly energy meter should I choose?

The product figures above refer to the supported measurement range of the current transformers. They are not the current that can be switched directly through the energy meter.

What is the difference between single-phase and three-phase energy monitoring?

A single-phase electricity supply normally has one live phase and a neutral. A single-phase energy meter measures the voltage and current associated with that phase. A two-channel single-phase meter can monitor two different conductors or energy flows on the same phase, but this does not make it a two-phase or three-phase meter.

For example, the two channels of Shelly EM Gen4 could be used to monitor the incoming supply and a solar PV circuit, or the overall supply and a significant load such as an EV charger. The current transformer selected for each measurement point must be appropriate for the maximum expected current.

A three-phase supply has three live phases. A three-phase meter measures each phase separately and combines them to create an overall view of the installation. This allows the system to show how demand is distributed between phases rather than assuming each phase is carrying the same load.

That distinction is important. A three-phase building may have different loads connected to each phase, and those loads will start, stop and change independently. Measuring one phase and multiplying the result by three will therefore not provide reliable whole-building consumption data. A purpose-designed three-phase meter also makes it easier to monitor phase-specific voltage, current, power and import or export direction from one device. Supported Shelly 3EM products can additionally identify phase-sequence errors.

How can I tell whether a property has single-phase or three-phase power?

The supply should be confirmed at the origin of the installation rather than inferred from the size or use of the building. A large house can still have a single-phase supply, while a small workshop may have three-phase power for machinery or other high-demand equipment.

UK Power Networks advises that a single-phase service head will typically have one supply fuse, while a three-phase arrangement will typically have three. However, the incoming equipment, metering arrangement and project documentation should be assessed by a qualified electrician before any monitoring system is selected or installed.

The number of consumer units is not, by itself, evidence of a three-phase supply. Several distribution boards may all be fed from the same phase. Equally, a three-phase site may contain many individual single-phase final circuits distributed across L1, L2 and L3.

Five questions to answer before selecting a Shelly meter

1. Are you measuring the whole supply or an individual circuit?

Whole-propertymonitoring normally requires CTs around the incoming phase conductors at an appropriate point after the supplier’s metering equipment. Circuit-level monitoring may instead be installed around the conductor feeding a specific EV charger, heat pump, PV inverter, lighting board or item of plant.

2. Is the measurement point single-phase or three-phase?

A single-phase circuit can bemonitored with Shelly EM Gen4 or Shelly Pro EM-50. A three-phase circuit or three-phase incoming supply should be measured across all three phases using a Shelly 3EM device.

3. What is the maximum expectedcurrent?

The CT range must suit the conductor being monitored. A 50 A meter may be appropriate for a PV inverter circuit or selected submain but may not be suitable for an incoming supply protected at 80 A or 100 A. Shelly’s current range provides 63 A, 120 A and 400 A three-phase options, while Shelly EM Gen4 supports compatible 50 A, 80 A and 120 A CTs.

4. Does the installation need Ethernet or Modbus?

Wireless connectivity may be sufficient for many homes and small projects. In plant rooms, commercial switchboards and integration-led projects, Ethernet can provide a more predictable connection and Modbus can simplify integration with a building or energy management system. This is where Shelly Pro EM-50 and the Pro 3EM range become particularly relevant.

5. Is the requirement monitoring only, or monitoring followed by control?

Understanding consumption and controlling a load are different functions. A meter can provide the information that an automation uses, but the final control method must be designed for the equipment involved. That may mean operating a suitably specified contactor, using a dedicated enable input, communicating through an API or passing the data to a wider control system.

Which Shelly meter is best for a single-phase supply?

Shelly EM Gen4: the flexible two-channel option

Shelly EM Gen4 provides two CT measurement channels for single-phase systems. It supports 50 A, 80 A and 120 A CT options, making it suitable for anything from selected circuits to higher-current incoming supplies, subject to the installation design.

Its two channels make it particularly useful where the customer wants to compare two related energy flows. Examples include grid demand and PV generation, overall consumption and EV charging, or a building supply and a significant heating load.

Shelly EM Gen4 also supports Wi-Fi 6, Zigbee, Bluetooth and Matter. It stores at least 30 days of one-minute data locally and includes a dry-contact output that can be used as part of an appropriately designed contactor-control arrangement.

Shelly Pro EM-50: professional DIN-rail monitoring

Shelly Pro EM-50 is a DIN-rail-mounted, two-channel single-phase energy meter. Both channels measure conductors on the same phase, and the product is supplied with two 50 A CTs.

The principal reasons to select Pro EM-50 are its professional panel format, Ethernet connection, Modbus TCP support and local historical data. It can store up to 60 days of one-minute records and includes a 2 A dry contact for contactor control.

Its 50 A measurement range must form part of the specification decision. Pro EM-50 may be ideal for two subcircuits, a suitably rated PV circuit or smaller incoming supplies, but it should not be selected for an 80 A or 100 A incomer if the monitored current could exceed the CT rating.

When should a 3EM be used on single-phase?

A three-channel Shelly 3EM may be appropriate on a single-phase installation where the objective is to monitor three independent circuits from one device. For example, an installer might want separate data for an EV charger, heat pump and electric hot-water system.

Both Shelly 3EM-63 Gen3 and selected Pro 3EM models support single-phase configurations. However, a 3EM is not automatically the better choice where only one or two measurement points are required. The additional channels, panel arrangement and cost should serve a defined monitoring objective.

Which Shelly meter is best for three-phase monitoring?

Up to 63 A per phase

For three-phase installations within a 63 A measurement range, there are two principal options.

Shelly 3EM-63 Gen3 is the compact choice. It can monitor a three-phase system or three independent single-phase circuits and stores up to seven days of one-minute data locally. It connects over Wi-Fi, with Bluetooth available for commissioning and inclusion.

Shelly Pro 3EM-3CT63 adds a professional DIN-rail format, Ethernet, Modbus integration and up to 60 days of local records. It uses a combined 63 A three-phase current transformer designed to fit over the three monitored conductors. The physical layout of the board should therefore be checked to ensure the combined CT arrangement is suitable.

Up to 120 A per phase

Shelly Pro 3EM 120A v2 is the general-purpose professional option for three-phase installations up to 120 A per phase. It is supplied with three 120 A CTs and provides phase-by-phase measurement, four-quadrant energy monitoring, optional phase-sequence detection and local data storage.

Typical applications include whole-building energy monitoring, larger residential supplies, commercial premises, three-phase EV charging, three-phase PV and projects where energy data needs to be integrated into a wider automation, BMS or EMS platform.

Up to 400 A per phase

For larger commercial or industrial incomers, Shelly Pro 3EM-400 extends the measurement range to 400 A per phase. It retains the professional connectivity, logging and integration capabilities of the Pro range but is supplied with three 400 A CTs.

This makes it the relevant starting point for higher-current distribution boards, larger buildings and plant where the current exceeds the operating range of the 120 A model.

Shelly meter selection by project type

Shelly EM Mini Gen4 is a monitoring-only device and does not contain a relay. It is intended for individual connected circuits up to 16 A rather than whole-property or three-phase monitoring.

Monitoring and load control are not the same thing

The current rating of a CT describes the range the meter can measure. It does not mean the meter can directly switch a 50 A, 120 A or 400 A load.

Shelly EM Gen4 and Shelly Pro EM-50 include dry-contact outputs intended for contactor-control applications. The load itself should be controlled through a suitably specified contactor or an approved control input rather than being routed through the energy-measurement channel.

The Shelly Pro 3EM products do not contain an integrated load relay. Where contactor control is required, the compatible Shelly Pro 3EM Switch Add-on provides a galvanically isolated dry-contact output for Shelly Pro 3EM and Pro 3EM-3CT63. The switching architecture, contactor rating, protection and behaviour under communications failure must still be designed for the particular load.

This distinction is particularly important for EV chargers, heat pumps, immersion heaters, motors and HVAC equipment. Some equipment can be safely enabled through a contactor, while other products require a manufacturer-provided control terminal, communications interface or managed shutdown sequence.

Installation and commissioning checklist

1. Confirm the supply and measurement point. Establish whether the incoming supply or selected circuit is single-phase or three-phase and identify exactly what the customer wants the data to represent.

1. Check the maximum current and conductor arrangement. Select a CT range that covers the expected current and confirm that the CT will physically fit around the intended conductor or board arrangement.

1. Match each CT to the correct voltage phase. In a three-phase installation, each current transformer must correspond with the correct phase-voltage input. Incorrect phase pairing can produce misleading power and energy readings.

1. Check CT direction and import/export values. Install each CT in the direction specified by the product documentation, then verify the result using a known load. Reversed CT orientation can cause consumption to appear as exported energy.

1. Validate and document the installation. Compare readings with other available measurements, label the monitored circuits and record the CT ratings, phase assignments, network settings and any automations created.

A connected energy monitor is not a replacement for the electricity supplier’s billing meter or the installation’s protective devices. Where measurements will be used for tenant billing, formal submetering, compliance or regulated reporting, the installer should establish the required metering standard and certification before specifying equipment.

Frequently asked questions

Can Shelly EM Gen4 monitor a three-phase supply?

No. Shelly EM Gen4 is a two-channel, single-phase energy meter. Its two channels can monitor two measurement points on the same phase, but a genuine three-phase supply should be measured using a Shelly 3EM product.

Can Shelly Pro 3EM be used on a single-phase installation?

Yes. Supported Pro 3EM configurations can be used to monitor up to three single-phase measurement points. This can be useful for submetering three important circuits, although Shelly EM Gen4 or Pro EM-50 may be simpler when only one or two channels are needed.

Which Shelly meter is best for solar PV monitoring?

For a single-phase PV installation, Shelly EM Gen4 can monitor two relevant energy flows, subject to correct CT selection and positioning. Shelly Pro EM-50 is an alternative where both monitored conductors are within 50 A and Ethernet or Modbus is required. For a three-phase PV installation or three-phase grid connection, Shelly Pro 3EM is the appropriate product family.

The exact measurement points depend on whether the customer wants to see PV generation, total building consumption, grid import and export, or all three.

Which Shelly meter should be used for an EV charger?

The answer depends on the charger and the measurement objective. A single-phase charger can be monitored using a suitable single-phase Shelly meter. A three-phase charger should be monitored across all three phases with a Shelly 3EM product.

Where the meter will contribute to dynamic load management rather than simply record consumption, the charger’s supported control method and the wider system architecture must also be considered.

Does a Shelly energy meter replace the supplier’s smart meter?

No. The supplier’s meter remains the billing meter. A Shelly energy meter provides additional local, phase-level or circuit-level information and can make that data available to the Shelly ecosystem or another automation platform.

Will installing an energy meter reduce electricity consumption?

Monitoring does not reduce consumption by itself. It can help homeowners, facilities teams and installers understand where and when electricity is being used, identify avoidable consumption and assess whether an efficiency measure has worked. When combined with appropriate automation, the data can also help loads operate at more useful times or switch off when they are not required.

Phase first, current second, application third

The simplest way to select the right Shelly energy meter is to follow a clear order:

Confirm the supply phase. Check the maximum current. Define the required measurement points. Choose the connectivity. Then decide whether the project needs monitoring alone or monitoring linked to control.

For most single-phase projects with one or two measurement points, Shelly EM Gen4 will be the natural starting point. Shelly Pro EM-50 is better suited to professional DIN-rail installations where two 50 A channels, Ethernet and Modbus TCP are required.

For three-phase monitoring, Shelly 3EM-63 Gen3 and Pro 3EM-3CT63 cover applications up to 63 A, Shelly Pro 3EM 120A v2 covers installations up to 120 A per phase, and Shelly Pro 3EM-400 extends the approach to higher-current commercial and industrial systems.

By selecting the meter around the electrical installation rather than simply the building type, installers can give customers energy information that is accurate, useful and ready to become part of a wider automation or energy-management strategy.

Explore the complete Shelly energy-metering range.

Products connected to fixed wiring, consumer units or distribution boards must be selected and installed in accordance with the relevant product documentation and applicable electrical regulations. Installation and commissioning should be carried out by a suitably qualified professional.