I'm planning to design a few low voltage DC hobby circuits (<12V) that I want to put in metal project box/enclosures. I intend to power the circuits with regulated AC/DC adapters (Wall Warts). Being that the power supplies will be isolated, can I stick with the floating ground approach I use in plastic enclosures or must I establish a single point chassis ground? Any advice regarding what the rule of thumb is would be greatly appreciated!

 

I'm planning to design a few low voltage DC hobby circuits (<12V)

How many different volts you want and their purpose are?
How many adapters that you want to prepare?
Like as 3.3V, 5V, 9V, 12V and the current is xA?

Being that the power supplies will be isolated, can I stick with the floating ground approach I use in plastic enclosures or must I establish a single point chassis ground?

If you mean that the low voltage side less 12 Vdc then it should be ok and no any special rules, sometimes for the application is case by case, if you want then you can prepare a flat metal for the common ground, my DIY power supplies almost used the metal boxes as this, but the one for backup usage was used the universal flat plastic board as this.

 

You don't need to earth the box if you're using an isolated DC supply, it defeats the object of Total Isolation Cass II psus.

You can ground the Negative supply for signal input purpose.