Three devices can switch a load remotely: a smart circuit breaker, a smart relay module and a contactor driven by a remote switch. They overlap in function, and buyers mix them up constantly. The wrong choice costs either money (paying for protection you do not use) or safety (switching a 15 kW motor through a device rated for lighting circuits).
A smart circuit breaker replaces a conventional MCB in the distribution board. It combines three jobs in one device: overcurrent and short-circuit protection, remote on/off switching, and (on metering models) energy measurement. Our SMR1 Wi-Fi metering RCBO, for example, is a DIN-rail unit that protects a 63 A circuit, switches it from the app and logs voltage, current and energy with class-1 accuracy.
A smart relay module does only switching. It sits behind an existing wall switch or inside a distribution board and adds remote control to a circuit that is already protected by a conventional breaker. The AT-SY3 mini smart switch is the classic example: it makes an existing switch smart without touching the panel wiring, which matters in retrofit and rental situations.
A contactor is a heavy-duty electrically-operated switch. It carries no protection at all and is meant to be driven by a control signal. For three-phase pumps, compressors and anything above 63 A, the standard architecture is: a small 4G switch driving the contactor coil, and the contactor doing the heavy switching. Our AT-SY7 three-phase 4G switch covers loads up to its rating directly; bigger loads take the coil-drive route described in our three-phase pump wiring guide.
Side-by-side comparison
- Smart breaker (e.g. ATQCB2, SY1): 6–63 A, full overcurrent protection, optional metering, occupies one DIN module. Choose it when the circuit needs protection anyway, or when you bill for energy.
- Smart relay module: 10–16 A per channel, no protection, zero panel space if hidden behind a switch. Choose it to retrofit existing circuits cheaply.
- Contactor + 4G switch: 9 A to 400 A+ depending on the contactor, no protection, needs a control circuit. Choose it for three-phase and high-current loads.
The three decisions in order
First, does the circuit need new protection? If you are wiring a new circuit, a smart breaker is almost always right: the protection is mandatory, so the smart part is nearly free. Second, is the load three-phase or above 63 A? Then a contactor driven by a 4G switch is the only correct route. Third, is this a retrofit where the panel must stay untouched? Then a slim retrofit unit such as the AT-SY3 mini smart switch wins.
When the cheap option is the right one
For pure lighting with many circuits and no motor loads, one relay module per circuit is dramatically cheaper than a smart breaker per circuit. Conversely, do not put a relay module on a pump circuit: if the conventional breaker upstream trips at night, the relay will happily re-close at the next schedule and run the pump dry. A metering smart breaker shows you the trip in the app because the current drops to zero while the switch command stays on.
If you are unsure which of the three fits your load, send us the nameplate — power, voltage, phase and starting method — and we will come back with a recommendation and a wiring sketch. Start here, or read how to size a smart breaker first.