Grounds...

[mortos360]

Can you always put them together or are there any conditions where you should never combine them?

I am wondering if I can use my function generator to drive an transistor... the problem is, that my FG seems to have mainsGround while my power supply doesn't. The PS has a 3th yellow connector that is mainsGround, but I don't know I can just short that with the negative rail of the PS.. or can I?
I remember a video of Dave where he talks about the danger of connecting oscilloscope probes (positive probe tip) to mainsGround, but I don't remember anything about him talking if I can safely connect all grounds together.

If I had 3 different power sources.. like a LabPS a battery and some other device.. is it in general safe to connect all grounds together?


ps: I just watched Daves video again and it seems to be OK to short negative rail of the PS with the mainsGround.

[benemorius]

ps: I just watched Daves video again and it seems to be OK to short negative rail of the PS with the mainsGround.

Yup. I was going to recommend watching it again with your situation in mind. I believe all the answers are there.

The very reason that your power supply isn't permanently mains earth grounded (it's called floating) is so that you can hook it up to other things that are grounded. It's usually a good idea for safety reasons to have it grounded any time you don't need it to be floating, which is why it gives you an earth terminal right next to the negative supply terminal. This makes it easy to short them together. If you leave your whole circuit floating it may float to a high enough voltage (relative to earth) to harm you. For instance, this can happen if some equipment fails and shorts part of your circuit to live mains voltage. Your circuit likely won't care, but now it will be at mains potential waiting for you to touch it and get a nasty shock. Dave's video probably addresses this too. It might not be a bad idea to re-watch the video until you grasp everything he has to say.