Hello Ralf,

separateObj uses the same factory as the MoI function separate. So it smashes joined objects like segmented curves, joined surfaces and solids into the lower level e.g. solids into faces. Is your input atomic, nothing will happens. To intersect something you need at least 2 intersecting geometries at the input for intersect objects. e.g. a curve and a surface -> output point. If you want to have all edges of a brep you can use the extractEdges node. For an overview for most of the factories, have a look to the document hosted by Max, if you don't know it already.

http://moi.maxsm.net/api/

Have a nice day
Karsten