Actually it's pretty easy. There are rules to follow. I don't think the average electrician would have a clue how to balance the loads and calculate the currents in a delta as opposed to a wye configuration. Most of them have engineers do the planning and they run the pipe and pull the wire.
What do master electricians do?
Watch the wire pullers?
It's called electrical theory for a reason.
It really ticks me off when the electrons run through me rather than through the carefully designed circuits.
I've designed control systems for advanced HVAC systems since 1979. I am not an accredited "engineer," I am a technician. "I am wire puller."