[floatsome]

Back to basics. Here is a simple, theoretical schematic. I've never had formal training in electricity beyond high school physics, and I don't want to presume anything.

1. The engine block is in the negative side of the DC system. What creates "boat ground potential" in that system -- the connection to the negative posts of the batteries? What is the relevance of the fact that the propshaft is in the ocean and electrically continuous with the engine block -- is that important in the nature of DC ground, or does "boat ground potential" in that circuit just mean return to the negative battery pole?

2. What happens if the boater unhooks black cable E from the starter mounting bolt in order to disable the engine circuit but leaves house circuit intact and switched on? Is the house circuit still "grounded" because cable F completes the house battery circuit to the house battery negative post?

3. ABYC E-11 states "11.5.4.7.4 If the negative side of the DC system is to be connected to ground, the connection shall be made only from the engine negative terminal, or its bus, to the DC grounding bus. This connection shall be used only as a means of maintaining the negative side of the circuit at ground potential and is not to carry current under normal operating conditions." What does "not to carry current" mean? Does not the black wire in a standard two-wire DC system carry current, and so the engine block also carries current for devices that ground through their metallic attachment to the block?