They're two small, cheap accessories that connect the same way: in parallel with the load. That's where the confusion comes from. But they solve opposite problems, and fitting the wrong one fixes nothing.
The quick way to tell them apart: the bypass is used when the load is too small; the RC Snubber, when the load is inductive.
Identify your problem
Find your symptom in one of the two columns and you have your answer. If it doesn't appear in either, the problem probably isn't solved by either of them.
When you need a bypass
Shelly devices that work without a neutral wire have to power themselves from somewhere, and they do it by letting a minimal current pass through the load itself.
With an old incandescent bulb that went unnoticed. With a 7 W LED, that current is enough to make it glow or flicker even when the circuit is off.
Shelly sets the threshold at 20 W: below that power, on installations without neutral, the bypass is necessary.
Affected devices: Shelly 1L Gen3, Shelly 2L Gen3 and Shelly Dimmer Gen3.
When you need an RC Snubber
Here the problem is the opposite: the load isn't small, it's inductive. Motors, fans, transformers, contactor coils or LED drivers.
When the relay opens, the coil resists the current being cut and sends back a voltage spike that can reach hundreds of volts in microseconds. That spike is what causes the Shelly to reset on its own, sparks to jump between the contacts or the contacts to end up welded together.
The snubber is a 100 Ω resistor and a 0.1 µF capacitor in series, with a nominal voltage of 600 V AC. It offers a momentary path for that energy to discharge without damaging anything.
The difference almost nobody explains
Both go in parallel with the load, but for different reasons:
- The bypass adds a permanent consumption (less than 4 W) so the device can power itself.
- The snubber doesn't consume under normal operation: it only acts at the instant of the cut, absorbing the spike.
That's why they're not interchangeable. A bypass doesn't dampen voltage spikes, and a snubber doesn't provide the current a neutral-less device needs.
Could I need both?
Yes, though it's rare. It would happen with a neutral-less device controlling a very low-power inductive load, such as a small ventilation motor. In practice, almost all installations need one or the other.
Frequently asked questions
My LED bulb keeps a faint glow
That's the typical bypass case, as long as your device is neutral-less. We go into it in the guide on why an LED flickers with a Shelly.
My Shelly resets every time I turn off the extractor fan
A clear snubber case. We look at it in detail in why a Shelly resets when switching inductive loads.
Do I need a bypass if my installation has neutral?
No. The bypass only makes sense on devices that work without neutral. If your Shelly is connected to neutral, it powers itself and doesn't depend on the load.
Is the snubber always needed whenever there's a motor?
Not necessarily. Shelly recommends checking the manual of the specific device. If your installation works normally, you don't need to add it preventively.
Can they cause a meter to register consumption with everything off?
The bypass can: it draws less than 4 W permanently and a meter sees it. The snubber shouldn't, as long as it's in parallel with the load and not with the relay contacts. If you have odd readings, also check the causes of why a Shelly meter reads more than expected.
Can they be installed in the electrical panel?
The bypass goes in the light fixture, next to the load. The snubber should also go as close as possible to the inductive load: mounting it in the panel reduces its effectiveness considerably.
Summary
- Flicker, glow or the device drops off Wi-Fi → Bypass for 1L/2L Gen3 or Bypass for Dimmer Gen3
- Resets, sparks or stuck relay → RC Snubber
- Not sure which bypass → guide to choosing a bypass
Still unsure? Tell us which Shelly you have, what it controls and what symptom you're seeing, and we'll tell you which one you need. Technical support in English and shipping from Spain.
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