bathroom anti mist mirror with leds

I have seen demister designs that are essentially a meander line of deposited resistance element printed onto a flexible film, stuck on the rear of the mirror like a big sticking plaster. The resistor is then across the mains. Such thing produce a few tens of picofarads of capacitance per square inch  between mains and the mirror glass. If it is one  of those, do not be tempted to try and peel it off to look  - the result is a no longer silvered mirror.

Depending how it is made, the mirror "silvering" may be conductive or not. The one thing it will not be is real silver, sadly.  If it is metal, then there is an effective  second plate to the accidental capacitor to the heater, and depending on the area, the impedance between it and live may be low enough for a tingle. Worse if the sticky back plastic has a nick in it, the mirror metal may be live.

 So does the voltage go away when the supply to the demister is removed - can you switch lights and demister separately ?


As noted already, when investigating possible shocks.  always assume the worst until proven otherwise - switches may be in the neutral, the  earthing of the house may be high Z, L-N polarity may be reversed. Probably not any of those, but keep one hand behind you while you do a quick sanity test to verify before wading in and assuming that flicking the light switch makes it truly safe to investigate.

Assuming it is the mirror that is a bit live, and it's supply and switching  etc is fine, maybe take some pics of the internal wiring - we may be able to help better if we can see it.

I have seen demister designs that are essentially a meander line of deposited resistance element printed onto a flexible film, stuck on the rear of the mirror like a big sticking plaster. The resistor is then across the mains. Such thing produce a few tens of picofarads of capacitance per square inch  between mains and the mirror glass. If it is one  of those, do not be tempted to try and peel it off to look  - the result is a no longer silvered mirror.

Depending how it is made, the mirror "silvering" may be conductive or not. The one thing it will not be is real silver, sadly.  If it is metal, then there is an effective  second plate to the accidental capacitor to the heater, and depending on the area, the impedance between it and live may be low enough for a tingle. Worse if the sticky back plastic has a nick in it, the mirror metal may be live.

 So does the voltage go away when the supply to the demister is removed - can you switch lights and demister separately ?


As noted already, when investigating possible shocks.  always assume the worst until proven otherwise - switches may be in the neutral, the  earthing of the house may be high Z, L-N polarity may be reversed. Probably not any of those, but keep one hand behind you while you do a quick sanity test to verify before wading in and assuming that flicking the light switch makes it truly safe to investigate.

Assuming it is the mirror that is a bit live, and it's supply and switching  etc is fine, maybe take some pics of the internal wiring - we may be able to help better if we can see it.