Over the years I've seen where a duplex dwelling will have a single service drop supply 100 ampere Service Entrance conductors then split to two meters and the two meters (one for each half of the duplex) are feeding two service panels (one for each half of the duplex) grouped in one location. Let's say each panel is rated for 100a and the GEC is required to be minimum #8 cu. Since no one uses #8 for obvious reasons, the electrician will run a #6 out of each service panel to the water pipe electrode sometimes 50 feet away. Would we see this a paralleling of a #6 conductor? And if so, is there anything in the Code that prohibits paralleling of the GEC?
