@spydrop, @kennethlimcp, for the AC part you can use a full-wave bridge and drive an opto-isolator whose output will be a logic level that you can read. DC will not make it through the full wave bridge so for that, you will need something else.
DC cannot be detected by induction since inductive pickup requires a changing magnetic field. However, a non-invasive hall-effect sensor will pickup the static magnetic field induced by the DC current. Here is an example of a DC sensor breakout. You pick a sensor based on the amount of current you expect to sense so you may have to experiment to measure the -48VDC vs -20VDC current levels in order to pick the right sensor. 
You may also want to take a look at this for some ideas on the ring part.