So I have a +-15 V and a neutral switching power supply. As far as I can see the outputs are floating. The power supply has no earth connection. Voltage from negative terminal to neutral and to positive are 15V and there is a small Ac component of 0.8mV at 50hz.
What confuses me is if I measured from any of the outputs to earth taken from the mains I observe a 114 V Ac at 50 hz. This worries me a bit since I don't fully understand it. I measured the same for a different power supply and it was around 5 volts ac. I thought the DC side is meant to be insulated from the AC side and I read somewhere it could be something to do with decoupling capacitors inside but I don't understand it ?
So my question why have 114 volts AC and can I pull down the negative or the neutral to earth safely? I.e. ground the PS.
I'm using the power supply to power a number of opamps used for transimpedance amplifiers of photodiodes. Currently the power supply injects a lot of noise. My PCB ground plane is connected to the virtual ground of the opamps ( non-inverting input) and also to the neutral of the PS. My feeling is that if I connect the neutral of the PS to the mains earth I'd solve some of my problems but I'm not sure it's safe ( for my components) currently.