I'm building a Wi-Fi controllable light switch that will use rocker style (up/down) plastic buttons. My plan is to have all the electronics enclosed behind a metal gang plate (the part that screws onto the gang box) in it's own plastic enclosure.

I would like to have plastic 'legs' on the back of the rocker switch (for up/down) that protrude into small holes in the single metal gang plate so that the plastic legs push tactile switches on the inside PCB, mounted behind the metal plate in the enclosed area. The depth of the holes is roughly 1.25 cm.

Some of the sensing electronics I'd like to keep mains referenced, so a non-isolated power supply would be preferable. I would like to have this UL certified eventually.

My question is simple. Do I need an isolated power supply in this case? The buttons will only ever be pressed by the plastic 'legs', not touched by a finger and everything else is enclosed.

Don't get me wrong, I have experience designing switching mode isolated power supplies in the past. But am not too sure of what I'll need in terms of certification for this specific case.

Any help / clarification / expertise is appreciated. Thanks.


1 Answer 1


From the point of view of users' safety, during manual operation, a Wi-Fi controlled switch is no different from a standard switch. Hence an isolated power supply would not be required. Isolation would also entail an increase in size and cost.

You would also need to factor in the requirement of a 2- wire switch as a replacement for a standard 2-wire switch (without neutral wire). The standby current of a 2-wire Wi-Fi switch would not light up a high wattage incandescent lamp but could cause a dull glow in low wattage LED bulbs.

A metal gang plate could hinder Wi-Fi access.

  • \$\begingroup\$ Thanks for the response. From the point of view of users' safety, during manual operation, a Wi-Fi controlled switch is no different from a standard switch. This is what I was thinking as well. A metal gang plate could hinder Wi-Fi access. Do you think I could forgo the holes in the metal gang plate and have a larger opening (still keep the legs on the rocker) in order to improve the propagation of Wi-Fi signal? \$\endgroup\$ May 26, 2020 at 13:17
  • \$\begingroup\$ Standard switches have two insulation layers, so even when the faceplate is taken off or destroyed you don't come into contact with mains power easily. Basically, expect a kid to break the faceplate by accident and then get curious about the holes. \$\endgroup\$ May 26, 2020 at 13:45
  • \$\begingroup\$ @SimonRichter I was thinking about this scenario as well. I assume UL will be too. I suppose the challenge now is to think of a way I could still use a non-isolated power supply and provide the secondary insulation layer, while still allowing the rocker legs to press the buttons some how. \$\endgroup\$ May 26, 2020 at 13:54
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    \$\begingroup\$ I think I found my answer. fccid.io/QGH-DDMX1/Internal-Photos/… Thanks a lot both of you! \$\endgroup\$ May 26, 2020 at 14:18
  • \$\begingroup\$ Anytime, AdvancedNewbie, I'm glad you got your answer! The integral assembly will avoid the problem, a user may have faced, of maintaining the required gap between the rocker actuator and the tactile switch. \$\endgroup\$
    – vu2nan
    May 26, 2020 at 18:07

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