You fit the device behind the switch, everything looks right, and when you turn the light off the bulb keeps a faint glow. Or worse: it flickers every few seconds, as though it were breathing.
You have done nothing wrong. It is a predictable consequence of combining a no-neutral device with modern LED bulbs, and it has one specific, cheap fix.
Where that current comes from
A Shelly needs current to stay alive: the Wi-Fi, the processor and the relay. Models wired to neutral take it from there, which is the natural thing. No-neutral models have no such option, so they take it from the only place left: through the bulb itself.
With a 60 W incandescent that did not matter — a filament never noticed a few milliamps. A 7 W LED is another matter: its electronics start on very little, and that residual current is enough to light it faintly.
The rhythmic flicker has an even more specific explanation: the current slowly charges the lamp’s internal capacitor until it reaches the threshold, the lamp flashes, the capacitor discharges, and the cycle starts again. That is why the interval is so regular.
The number that decides it: 20 watts
On devices that work without a neutral conductor, a load below 20 W needs a bypass. Above that, usually not.
Add up your light fitting before ordering anything. Three 5 W LEDs are 15 W and sit under the threshold. Six of them are 30 W and will probably behave. It is a ten-second sum that saves you ordering the wrong thing.
The four symptoms
- A glow with the light switched off. The most common and the easiest to recognise.
- Rhythmic flicker. Flashes at regular intervals, on or off.
- The device drops off the Wi-Fi when you switch off. It cannot get even the minimum current to stay alive.
- The lamp never lights fully. It sits at half brightness or does not respond.
The fix
The bypass connects in parallel with the load and gives that current somewhere else to go. The device still powers itself exactly as before, but the current no longer passes through the bulb — and the bulb goes properly dark.
It draws under 4 W and measures roughly 39 × 23 × 13 mm, small enough to sit inside most light fittings. It is a passive component: you wire it in and it works. There is nothing to configure in any app.
There are different versions depending on your device — the one for a no-neutral relay is not the one for a dimmer. Check which yours takes before ordering.
Rule these out before buying
A bypass solves one very specific problem. Make sure it is yours:
- Does your device work without a neutral? If it is wired to neutral, a bypass is not the answer and the problem lies elsewhere.
- Is the load under 20 W? If you have 40 W of LED and it still flickers, the cause is somewhere else.
- Have you tried a different bulb? Some very cheap LEDs flicker because of their own driver, Shelly or no Shelly.
- Is the symptom that the device restarts when you switch off? That is not a shortage of current, it is a voltage spike — and what you need is an RC snubber, not a bypass.
When the report arrives by phone
The third symptom — the device that falls off the network when the light goes off — has a recognisable signature from a distance. In the console, that unit’s last seen comes and goes: it disappears, returns, disappears. It is not a dead device, it is one losing its supply every time somebody hits the switch.
Telling «intermittent» from «dead» before you set off decides whether you take a bypass in the van or a replacement device.
Common questions
What if I just fit a more powerful bulb? It works, but it is the worse deal: you spend more electricity permanently to avoid a one-off accessory that draws under 4 W.
How many do I need? One per controlled circuit, not per bulb. If one device governs two circuits and both sit under 20 W, you need two.
Does it get hot? It dissipates some heat, like anything that consumes energy. It tolerates up to about 70 °C, but do not seal it into an unventilated void.
Can I fit it myself? It means working on the light fitting’s wiring. Switch off at the board and verify the absence of voltage before touching anything. If you are not confident, have an installer do it.