Every switching device has a maximum load it can safely connect and disconnect without causing damage to the switch contacts. Therefore there is a limit to how many devices can be connected dependent upon their individual load ratings. No switch can operate an infinite quantity of lamps, there will always be a limit. Cable sizes and protective devices will be calculated proportional to the load, cable length any correction factors etc. (as Steptoe pointed out).This should all have been covered during the typical cable calculations done at college. Do they no longer teach the basics how to design a circuit based on all the normal criteria? This used to be regular part of the C&G coursework. such as 'What is the minimum size cable to a load x, y meters from CU, run in conduit, then buried under thermal insulation, then in a loft void with ambient temp of z degrees etc, etc.' I would be very shocked if this is no longer covered on electrical courses.
Doc H.