These two concepts are commonly confused. Sometimes with lethal results. The confusion exists even in the NEC. But the NEC also has the solution. Wherever you read “grounding” in the NEC, refer back to the Art. 100 definitions.
The NEC says all non current-carrying metal parts of fixed, portable, and mobile equipment “shall be grounded” [250.190(A)]. But does it really mean this?
Article 100 says that “grounding” means a connection to the earth. So the answer is no.
Yet read just a bit past 250.190(A) and you find requirements for the “equipment grounding conductor” [250.190(C)]. What’s going on?
Because of the Art. 100 definition, the “equipment grounding conductor” that’s mentioned in so many NEC Articles (in Chapters 2, 3, 4, 5, and 6) isn’t really a “grounding” conductor.
One major purpose of this conductor is to eliminate differences of potential between pieces of electrical equipment. You’re not going to accomplish that by relying on earth connections.
But you will accomplish that if you create a low-impedance path between equipment (and between the other items listed in 250.190(A)). You can create that low-impedance path with an electrical conductor.
Going back to Art. 100, we see five entries that begin with the word “bonding”. We’ll discuss bonding terms in Part 2.