The Pro EM-50 is the smallest meter in the Pro range, and the only one with a built-in relay. Those two facts explain almost every question it raises: people buy it expecting it to measure more than it does, or expecting the relay to take more than it can.
If you already have one and what you want is the fitting, that is in how to install the Shelly Pro EM-50, step by step.
Can I measure the whole house supply with it?
Only if it stays under 50 A per channel, which single-phase is about 11 kW. For a home on a normal contracted capacity that is plenty; for a larger supply or an industrial board you will fall short and want the Pro 3EM, which reaches 120 A.
The limit is not a guideline: above that current the clamp saturates and the reading stops meaning anything.
Can I wire a water heater or a radiator to the relay?
No, and this is the mistake that has killed the most units. The Pro EM-50’s relay takes 2 A maximum at 240 V. It is a control contact, not a power one.
An electric water heater draws around 9 A. Wiring it directly is not stretching the margin: it is four and a half times what the contact can break. The contacts weld, and a welded relay cannot be repaired.
The correct arrangement is for that relay to drive a contactor coil, and for the contactor to handle the load. It is set out in when to replace the relay with a contactor, including the RC snubber the coil needs.
Will 120 A clamps work?
No. The unit is calibrated for 50 A transformers, and that calibration is part of the measurement. Fit a clamp of a different range and the reading comes out consistent but wrong — the worst kind of error, because nothing about it looks broken.
How accurate is it?
- 1% between 5 and 50 A — where it will spend nearly all its time.
- 2% below 5 A.
That 2% on small loads is worth keeping in mind: if you are watching a 100 W draw the absolute error is tiny, but as a percentage it shows. None of these meters is fit for billing; for knowing what each thing costs you, they are more than enough.
Does it do three-phase?
No. It is single-phase. It has two channels, but both share one voltage reference, so it cannot measure three independent phases.
For three-phase there is the Pro 3EM with separate clamps up to 120 A, or the Pro 3EM-3CT63 with a combined clamp up to 63 A.
Does it need internet to work?
No. It measures and stores on its own: it keeps at least 60 days of history at one-minute resolution in its own memory. If the network drops it carries on recording, and when the connection returns there is no gap.
That matters more than it sounds where the consumer unit is far from the router: you are not depending on good Wi-Fi to avoid losing data.
Can I extend the clamp cable?
You can, but it is one to avoid. That cable carries a small signal, and the longer it is the more electrical noise it picks up — especially inside a board full of contactors and drives. Keep it short, and if it will not reach, move the meter rather than extend the clamp.
Reading the history without opening the board
The 60 days the unit stores can be read from the console without opening the board or connecting to its IP. That is where you see whether the consumption worrying you is constant or comes in spikes — which is exactly what separates a real problem from an impression.
Both the console and the app work with Gen2, Gen3 and Gen4 devices, not only the models named here.
How to use both, section by section: mobile app manual and web console manual.