Are common grounds safe?

[Braeden Hamson]

In my projects I tend to tie all of my grounds together and call it a day. I'm pretty sure this is safe most of the time, but I'm wondering if there is a case where it's not okay to put all the grounds together. Off the top of my head I'd say don't tie a DC ground to an AC ground. And I get a bit unnerved putting a high voltage say 24v ground to a 5v ground. I've often considered putting a diode between my ground and circuits that way electrons don't flow backward through my circuits.

 

[kellys_eye]

Common grounds are perfectly acceptable in most cases - even with high voltage differences. The only occasions where you need to take extra care is in circuits that have specifically seperated analog and digital grounds.

Audio circuits may need care to prevent earth loops (hum) and high current power supplies need care too.

You can't 'feed back' a voltage through a ground circuit (in your example from 24V to 5V) the conventional current flow is from supply positive to ground and once at ground.... that's it.

 

[Minder]

For the most part, there are two schools of though, one to keep all parts of the system isolated, and the other to set up common grounds.
I prefer the latter, and when setting up control panels that contain control electronics, I set up a common star ground point for all the ground references together with the service earth ground.
So far it has kept me out of trouble!
M.