power supply grounding

[minibutmany]

Hello,
I have thought about building a bench power supply, as I have gone a long time without one. I wanted it to have both positive and negative 12V rails as well as a variable one, probably using an LM317. I wanted it to be as oscilloscope safe as possible, but i wasn't sure what needs to be done in terms of grounding. Is it possible to completely isolate the supply from ground while still having both positive and negative rails?
Thanks

[SebG]

How will you be generating the negative voltage.  If you are using a transformer with a center tap as the ground you will get a positive and negative voltage (after diode bridge).  A transformer will isolate the AC Line (Hot and Neutral).  As long as you don't connect the earth ground to your power supply ground you will have an isolated device.  If you are using a switching supply to power your circuit, it might not be isolated from neutral or earth ground.  You would need to isolate the voltage somehow (using an isolation transformer for example or use an isolated switching power supply)