An instrument ground is sometimes referred to as an isolated ground.

The cello is such a melancholy instrument, such an isolated, miserable instrument.

I like to work my camera as if it were a musical instrument.

It's not necessary to go down there and hang out down there, ... This wasn't an isolated incident in that neck of the woods.

For governments at war, the media is an instrument of war or an element in war that is to be controlled.

We're all attempting to keep our feet on the ground.