I've recently came with a dirt cheap (and with that I really mean dirty!) design for a mains operated device
It has a transformerless PS (way dirty) and some stuff on the inside that consumes roughly 20mA as an absolute maximum.
The device in question needs to be woke up with a 220V signal and once it's energized it retains
it's source by means of a relay while doing some stuff. Then it releases the relay powering itself off.
IMHO this device is complete isolated, with no metal parts accessible whatsoever.
My question is, since this startup signal must be derived from 220V, if it's advisable to use a tact switch for a production run
(RA switch with 18mm stem and plastic cap). Any other switch (as far as I could find) will add too much to the cost.
However I designed the startup circuit with a 4700 ohm limiter resistor in series to the switch and a varistor before the switch, my main concern
comes from the eventuality of internal arcing started with a line transient, since this kind of switches uses to have contact ratings of 50mA@24VDC
For now I prototyped the circuit, with such a tact switch and it works like a charm, its permanently connected to the line and I power it 3-4 times at day and it works,
but I can't tell how many time it will work ok
Any experience with these switches?