A Shelly energy monitor shows what a circuit, or the whole supply, is drawing. The seven we stock are not the same job. Some sit in a wall box. Some clamp a three-phase board. Only some can switch a contactor. Fitting any of them to the mains is work for a competent electrician.
Start with the phases, then the space you have. The model follows from that. For how Shelly bodies differ more widely, see Shelly Mini vs Pro vs BLU vs Wave.
The short answer
- One circuit in a wall box, up to 16 A, current through the device: the Shelly EM Mini Gen4.
- One or two single-phase circuits on clamps, plus a 2 A contact: the Shelly EM Gen3.
- A three-phase board up to 63 A, on the breakers: the Shelly 3EM-63W Gen3 or the Shelly 3EM-63T Gen3.
- Two DIN clamp channels, up to 50 A, with a built-in 2 A relay: the Shelly Pro EM - 50A.
- Whole supply on a DIN rail, with 63 A, 120 A or 400 A clamps: the Shelly Pro 3EM.
- A contactor from that Pro 3EM needs the Switch Add-On. The meter has no relay.
One circuit or the whole supply
The EM Mini Gen4 has one live and one neutral, and the load current passes through it. Shelly rates it at 0 to 16 A, and 3840 W. It is for one circuit in a wall box, not a house incomer.
The EM Gen3 is single-phase and measures with clamps. Shelly calls it two channels, with up to two current transformers. A 50 A clamp is included. An 80 A clamp is listed as compatible. Use it for two circuits whose current fits the clamp.
The 3EM-63W Gen3 and 3EM-63T Gen3 measure three phases at once. Each phase has an integrated transformer, rated 0 to 63 A, with saturation noted at 130 A. They sit on the breakers, not in a wall box.
The Pro EM - 50A is two clamp channels on a DIN rail, rated 0 to 50 A. It is for two circuits, not a three-phase incomer.
The Pro 3EM is the DIN meter for the supply. Shelly says it can be three-phase or single-phase. We sell it with 63 A, 120 A or 400 A clamps. Choose the clamp from the current you expect.
Single-phase or three-phase
Most UK homes have a single-phase supply. Some, often larger properties, have three-phase. The meter has to match the supply.
The EM Mini Gen4, the EM Gen3 and the Pro EM - 50A are single-phase. The EM Gen3 and the Pro EM - 50A each have two channels on that one supply. They can see two loads. They cannot see three phases.
The 3EM-63 models have three live inputs, LA, LB and LC, plus neutral. Shelly rates each phase at 0 to 63 A.
The Pro 3EM lists both three-phase and single-phase wiring. It has clamp inputs for three phases and an optional neutral. On one phase, Shelly's diagrams use the channels for separate circuits, such as the supply and a solar feed.
DIN rail, breaker, or wall box
The EM Mini Gen4 is 29 x 34 x 16 mm and mounts as a wall console. Shelly also says it fits very small spaces, including a wall box. The load conductor goes through its terminals.
The EM Gen3 is 37 x 42 x 16 mm. Shelly lists a wall console, an electrical cabinet, or a wall box. The clamps sit on the cables.
The 3EM-63 pair mounts above or under the DIN breakers. It is not a standard DIN module. Phase conductors pass through an 8 mm aperture. The 63W is 21 x 54 x 42 mm without its wires. The 63T is 31 x 54 x 42 mm without its wire.
The Pro EM - 50A and the Pro 3EM are DIN-rail bodies, 94 x 19 x 69 mm.
When you need a contactor
Measuring and switching are different jobs. A meter that only reports cannot open a contactor.
The EM Mini Gen4 has no relay. Neither 3EM-63 model lists a switching current. They report. They do not switch.
The EM Gen3 has one dry contact, rated 2 A at 240 V. That can operate a contactor coil. It cannot carry a cooker, a charger or a heat pump.
The Pro EM - 50A has a built-in relay, also rated 2 A. It has Ethernet as well as Wi-Fi.
The Pro 3EM has no relay. Shelly says contactor control needs the Switch Add-On. It clips to the meter, takes 3.3 V and 12 V from it, and switches up to 2 A AC or 2 A DC.
The seven monitors side by side
Shelly EM Mini Gen4. Single-phase, one circuit. Current passes through the terminals, up to 16 A and 3840 W. Wall box. No relay. Wi-Fi, Bluetooth 5.0 and Zigbee. At least 10 days of one-minute data.
Shelly EM Gen3. Single-phase, two channels. Clamps: a 50 A transformer is included, and an 80 A transformer is listed as compatible. Wall box or cabinet. One dry contact at 2 A. Wi-Fi and Bluetooth. At least 10 days of one-minute data.
Shelly 3EM-63W Gen3. Three-phase, three channels. Integrated clamps, 0 to 63 A each phase. Sits above or under the breakers, and connects with colour-coded wires. No relay. Wi-Fi and Bluetooth. At least 7 days of one-minute data.
Shelly 3EM-63T Gen3. Same ratings as the 63W. The difference is the connection. Shelly calls this the flat-terminal model. The terminals share the breaker screws with the phase conductors. No relay. Same storage and radios as the 63W.
Shelly Pro EM - 50A. Single-phase, two channels. Clamps rated 0 to 50 A. DIN rail. Built-in 2 A relay. Ethernet, Wi-Fi and Bluetooth. At least 60 days of one-minute data.
Shelly Pro 3EM. Three-phase or single-phase. Separate clamps: 63 A (3CT63), 120 A, or 400 A. DIN rail. No relay, unless you add the Switch Add-On. Ethernet, Wi-Fi and Bluetooth. The 120 A version stores at least 45 days of one-minute data. The 63 A and 400 A versions store at least 60 days.
Shelly Pro 3EM Switch Add-On. Not a meter. It attaches to a Pro 3EM on the DIN rail and switches up to 2 A. Power comes from the meter, not from its own mains supply.
Common mistakes to avoid
- Buying the EM Mini for a house incomer. Measurement stops at 16 A, and the conductor has to pass through the device.
- Using an EM Gen3 or a Pro EM - 50A on a three-phase supply. Both are single-phase meters with two channels.
- Ordering a 3EM-63 without checking the breaker. The 63W uses wires. The 63T uses flat terminals that share the breaker screws. The ratings are otherwise the same.
- Putting 63 A clamps on a supply that can run well above that. The Pro 3EM body is the same. The clamp rating is the limit.
- Expecting the Pro 3EM to switch a load. It has no relay. The Switch Add-On, or a different meter with a 2 A contact, does that job.
- Treating a 2 A contact as a power switch. It operates a contactor coil. It does not carry the cooker, the charger or the heat pump.
Can one Shelly energy monitor see the house and the solar?
Only if it has two channels, and both currents are inside the clamp rating. The EM Gen3 and the Pro EM - 50A each have two clamp inputs on one phase. Shelly's Pro 3EM diagrams also show a single-phase supply beside a solar feed. These are current readings, not an export figure or a tariff rule.
Will these work with Home Assistant on the local network?
Yes. These monitors are Wi-Fi devices, and the Pro models also have Ethernet. They can be used on the local network without the cloud. Our Shelly and Home Assistant guide covers what that means in practice. The EM Mini Gen4 also has Zigbee. The others in this list do not.
Do I need the Pro 3EM Switch Add-On?
Only if the Pro 3EM must operate a contactor. The meter does not switch by itself. The add-on switches up to 2 A and takes its power from the meter. If you already have an EM Gen3 or a Pro EM - 50A, that 2 A contact is built in. You do not add this unit to those.
Shop the Shelly energy monitors
One circuit in a box: Shelly EM Mini Gen4. Two clamp channels and a 2 A contact in a box: Shelly EM Gen3. Three-phase on the breakers: Shelly 3EM-63W Gen3 or Shelly 3EM-63T Gen3. Two DIN channels up to 50 A: Shelly Pro EM - 50A. Whole-supply DIN meter: Shelly Pro 3EM, plus the Switch Add-On if a contactor has to follow it.