Came across this plumbing component this morning. Water was dripping through the drain pipe. Had to break the photos into two due to shelving located in front of the wall. Could someone explain the purpose of this component? Should water be continuously dripping? Thanks. 
It’s a watts pressure relief valve(adjustable.
Sometimes used in place of a an expansion tank in some jurisdictions.
Is it normal to continually drip? Why the pressure relief valve at this location just above the main water shut off valve?
No, it should only discharge when the pressure setting it exceeded. It probably needs replacement.
Thanks Michael.
Also, with the leg terminating their, that outlet box may not be in the safest spot. Just a thought. It probably meets all the specs and blah blah blah. But you never know what could happen.