My main amp is plugged into a dedicated grounded circuit and all is fine....
However, I would like to be able to use another amp without having to plug and unplug
and the other outlets in my home do not have a grounded receptacle, however there
is a bare copper wire that goes from steel box to steel box in most cases.

The worst case scenario is that it is ungrounded.

I usually don't play when soaking wet- is there a concern here?