The "how is it done" will depend on how the existing branch circuits are wired, and how the associated conduits are routed. The electrician doing the installation will have to determine where to tap into the existing circuit. If you wish to describe the process in the study report you are writing, I would suggest using the "precision ambiguity" approach (an invention of my own, but feel free to plagiarize). The concept is to admit that there are unknowns, while asserting that you are aware of exactly what things are unknown.