The RC Snubber has no configuration and no polarity. Like the bypass, it all depends on where you put it, and here the location matters more than it seems.
Before you start
Cut the supply at the corresponding breaker and verify the absence of voltage before handling anything.
Be clear about which load you're going to protect. The snubber is installed per inductive load, not per Shelly device.
The rule that decides everything
Shelly states it expressly: as close as possible to the inductive load. Not in the panel, not next to the Shelly.
The voltage spike is born in the motor coil. If you dampen it right there, it doesn't get to propagate. If the snubber is ten meters away inside the panel, the spike travels the whole cable before reaching it, and along the way it has already generated interference and disturbed the Shelly's power supply.
Step by step
- Cut the power and verify it with a multimeter.
- Locate the inductive load's terminals: the junction box of the motor, the fan or the contactor.
- Connect the snubber in parallel to those two terminals, between the relay output and the circuit's neutral. It has no polarity.
- Insulate the connections with heat-shrink or insulating tape. Shelly insists on this point in its support documentation.
- Secure the assembly so it doesn't hang from the wires or rub against moving parts.
- Restore the power and switch the load several times, checking that the Shelly no longer resets.
The mistake that multiplies problems
There's another classic way to fit a snubber: in parallel with the relay contacts instead of with the load. It's valid in other contexts and that's why many people apply it out of habit.
Not here. With a 0.1 µF capacitor, that position lets through about 7 mA permanently at 230 V even with the relay open. Consequences: LED bulbs with a ghost glow and meters that record consumption with the circuit off.
Specifications
- Capacitance: 0.1 µF
- Resistance: 100 Ω
- Dissipation: 1/2 W
- Nominal voltage: 600 V AC
Frequently asked questions
Can I install it in the panel if I can't reach the motor?
It'll work partially, but you'll lose a good part of its effectiveness. If access to the load is impossible, place it as close as you can to the end of the circuit.
Does the order of the wires matter?
No. It's a passive component with no polarity.
Do I need one per channel or one per load?
One per inductive load. A Shelly 2PM Gen3 with two motors needs two.
Does it get hot?
Barely. Its nominal dissipation is half a watt and in normal operation it works well below that, because it only acts at the instant of the cut.
Is it good for DC loads?
It's rated for 600 V AC. In DC, the usual protection against inductive spikes is a flyback diode, which is a different component.
Does it need checking over time?
Shelly's support documentation recommends periodically inspecting snubbers and their connections to ensure they keep protecting.
Related products and guides
Installation by qualified personnel. Working in a motor's junction box requires electrical knowledge: if in doubt, use an authorized installer.
Leave a comment