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SW input incorrectly recognizes ON

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Dear Forum,

I would like to use my Shelly to query the status of a light switch.
The switch output is connected in parallel to the light to be switched.
If the switch is set to OFF, the SW input of the Shelly recognizes this as ON.
Is this a HW error?


Kind regards

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Posted (edited)

No, it’s a feature, not a bug! The intention of the developers was to arrange that a SW input is activated by live potential AND by neutral potential. Thus, the neutral potential via the lamp (in off state) activates the SW. Switchithe lamp on, live potential across the manual switch activates the input either.

Remedy is achieved by (a) an intermediate relay, whose NO contact may activate the SW input, or (b) by a resistor dropped in the wire from manual switch to SW terminal:


If desired, I gladly help with a  twofold isolated wire with resistor, ready for installation. 


Edited by thgoebel
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Thank you very much for your explanation.
Have you tested the solution with the resistor?
If the SW input evaluates potentials and practically no current flows at this input, a series resistor will not help from my point of view.

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Yes, indeed, this is tested.

Aim of the resistor is, to prohibit an activation of the SW input with live potential. Thus, only N-potential shall activate the input. Switching the lamp on leads live potential at SW and deactivates the input. This behaviour inverts the switching logic. Hence, the input has to be configured as „Reverse Input“ to correct the inverse logic.

Some details to the method of preventing live potential to activate the input: Activation is done by a very small current (approximately 37μA) which is flowing from terminal SW to L if the manual switch is operated. This current is driven by 3V DC. The resistor inhibits this current flow, but allows enough current with the potential of 230V AC which is present between SW and N whilst the manual switch is in off position.

You may find further details by searching for „Bukowski Draht“ in the web…


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I think I have a similar issue but cannot identify the problem.

I want to fade in/out an LED stripe controlled by an OPTONICA LED V1-F


(because Shelly RGBW2 does only support 3000ms fade)

I am using this circuit.

20240705_1627213.thumb.jpg.6604d8cc020089a20bb3237515932c74.jpgShelly is configured with auto-off after 0.5sec to generate a pulse for the controller. 

I am facing the problem that when I simulate the PIR by connecting L and Lout stripe manually it works fine but when I use the PIR the Shelly does not switch.

Anybody has an idea why?



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Most likely the PIR has either an electronic switch or a internal circuit which leads neutral potential at its output. Moreover, some PIR devices need a minimum load.

You may experience with the above mentioned resistor. In the case this will show no effort, you should add (for test purposes only) a incandescent bulb at the output of the PIR. If this is successful, you may replace the test bulb with a so called „Grundlastelement“. This is offered (amongst others) by ELTAKO.

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With the resistor, the SW input is activated with neutral potential only. Thus, “reverse input“ has to be configured to correct the switching logic. And: The Shelly Mini 1 has to be Gen3, cause the (out-of-stock) Shelly Mini 1 Gen2 has an error in printed circuit board. 
Does the test bulb light up if PIR is engaged?

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