LED Light Buzzing After Shelly Install

    Hello! I have a slightly unusual 3-way (US) light that I wanted to smarten. There aren't enough wires in the the walls for me to connect both of my wall switches (momentary switches) to Sx so I read that they can be connected to N instead. I've done this and it works but now there is a very noticeable buzzing when the light is on. Previously, the switches were standard, dumb 3-way switches and I tried re-wiring the 3-way with a TP-Link Kasa 3-way switch on one end just to check but neither of these circumstances created the buzzing; just with the Shelly 1L. Any idea why this is happening? Diagram attached.

    Welcome to the forum!

    Switching the SW input of a Shelly 1L with neutral potential drives a current of approximately 2,2mA through the innards behind terminal SW. This is substantially a resistor of 47kΩ and a diode. Hence, the Shelly is loaded with an extra dissipation loss of 280mW, which will drive the resistor to its limits! Consequently, I would not recommend to wire the Shelly 1L in this configuration!

    Alternatively, a simple Shelly 1 would do the job: Both switches should handle live potential which can be easily managed by re-wiring the switches. The extra terminal I at Shelly 1 must be connected to live wire. The rest remains the same…

    Please have a look at the forum‘s lexicon section - you may find the appropriate wiring diagrams here!

    „Habt Geduld. Alle Dinge sind schwierig, bevor sie einfach werden!“ (aus Frankreich)

    „Nothing in life is to be feared, it is only to be understood.“ (Marie Curie, 1867-1934)

    „Es reicht nicht“, rief Schiller, „Gedankenfreiheit zu fordern, man muß auch denken können, sonst fordert man Gedankenlosigkeitsfreiheit und die ist die Freiheit zur Dummheit, welche wiederum die schlimmste Unfreiheit überhaupt ist!“
    (Aus „Besuch aus Weimar“ von Gert Heidenreich, Schriftsteller, *1944 in Eberswalde)

    For anyone reading the future: connecting the switches to L and Sw does not work. The switches can turn the light off but not back on. I have reverted to N and Sw with the intent to live with the buzzing.

    Re: Previous comment. The switches are momentary switches so any load they may create on the Shelly will be momentary. Additionally, and I should have mentioned this before, the LED driver is buzzing not the Shelly.

    The buzzing of the LED driver is a consequence of the very special switching system the Shelly 1L has: Due to the fact, 1L has to work without neutral wire, it contains not only a simple relay but a power transistor, which is involved in switching on and off. Very sensitive LEDs tend to flickering and or buzzing if connected with Shelly 1L.

    As I mentioned earlier, a simple Shelly 1 (or Shelly plus 1) would do a significantly better job in this scenario…

    And yes: Shelly 1L does not switch with SW connected to L! SW input must be switched to Sx or O (or N, if momentary buttons are used). You may find the appropriate diagrams in the „lexicon“ part of this forum.

    „Habt Geduld. Alle Dinge sind schwierig, bevor sie einfach werden!“ (aus Frankreich)

    „Nothing in life is to be feared, it is only to be understood.“ (Marie Curie, 1867-1934)

    „Es reicht nicht“, rief Schiller, „Gedankenfreiheit zu fordern, man muß auch denken können, sonst fordert man Gedankenlosigkeitsfreiheit und die ist die Freiheit zur Dummheit, welche wiederum die schlimmste Unfreiheit überhaupt ist!“
    (Aus „Besuch aus Weimar“ von Gert Heidenreich, Schriftsteller, *1944 in Eberswalde)

    As mentioned by thgoebel, the Shelly 1 or Plus 1 is a better. When lights flicker, or make noise they are telling you they are unhappy. best to put it back, and start over.

    A very useful tool that can be used to determine how three way switches are wired is a Non Contact Voltage Tester.

    The person that did this blog spent a great deal of time documenting US three way wiring. take your time and look at it:

    Smart Three Way Switch Installation | DIY Smart Home Guy

    Also, here is a picture of my switch installThree way shelly 1 Plus.jpg