Isolation (or not) in energy monitoring
The classic power monitoring circuit is the kill-a-watt.  It is a 'hot power supply' design.  Galvanic isolation is provided by the case (meaning: assume the traces on the inside are connected to the mains).  The user is kept safe by virtue of the plastic case.

Hot designs are done to save cost and space (transformers are costly and big, even in SMPS designs).  But you can't attached scope probes to them or you will trip your GFI.  To work on them, put an isolation transformer between the device and the mains.  Then your scope will work.

In hot designs, very often the ground planes is 'starred' so that separate sections of the design are isolated from one another.  This is done by picking a central ground point and running ground traces out to different sections.  This is how analog and digital grounds are connected together.