Tom
Far too many even so-called electricians can hook up power to something without the protection proper grounding provides. Yours is an excellent question, and you should be very comfortable with the answers you receive before you proceed with any electrical hook-ups. There are several good books on grounding that are written for the beginner and are easy to comprehend. The grounding of the system or circuit is simply put, the most important part of the connections that are made. These books will explain better than me the difference between: service ground, equipment grounding conductors, grounded conductors, neutral conductors, bonding, main bonding jumper, equipment bonding jumper, etc. along with proper sizing techniques. One common misconception is that the white conductor of a 12/2WG (common house wire ) is a neutral. If you have 12/2WG connected to a receptacle there is not a neutral involved this white wire is a grounded conductor. You would only have a neutral if you were using 12/3WG and connected two ungrounded conductors to different 120v legs which would produce 240v between them, and you used some 120v power to create a neutral which carries the unbalanced current. If you connected two 100 watt light bulbs to one 120v line and the neutral, and one 100 watt bulb to the other 120v line and neutral, the neutral would only carry 100 watts of current ( or the unbalanced current ) between the two 120v lines. If your white ( grounded conductor ) to the receptacle is broken and the black ( ungrounded conductor ) contacts the metal case of the equipment it is then that the ground ( equipment grounding conductor ) would trip the breaker ( overcurrent protection device ). The sad fact that is unknown to many installers is the grounding system does not operate until there is a problem such as a short or fault that requires its protection, and much too often this safety system has been improperly wired or is nonexistent. A common example of improper wiring is the grounded conductor and the equipment grounding conductor being connected under the same screw on the neutral buss. If this one connection is compromised, you loose both paths for fault current to return to the overcurrent protection device,without which the breaker will not trip. I hope this helps you as your question is not simple to answer even by a simpleton like me.
