What I want to stress in my over-simplified model is the critical need for the ground wires to ultimately be connected - at the service only - to the utility neutral.
It amazes me how many times I see the neutral bonded on sub panels!
Other folks will bond the neutral to the pipe, when there's no neutral wire convenient. A very dangerous practice - even if the two are connected at the main service!
And 90% of th time it is probably an old guy who does this!!
