In Part 1, we noticed the NEC often uses "grounding" when it means "bonding." Grounding is a connection to the earth. But what does bonding really mean, and what are the implications of the five bonding terms in Article 100?
The NEC defines first of those terms, “bonded (bonding)” as “Connected to establish electrical continuity and conductivity.” This leaves room for interpretation. For example, how much conductivity?
One purpose of bonding is to put metallic objects at the same electrical potential. You can achieve this only with low impedance bonding conductors. If you use a high resistance bond, then you will have a high enough voltage across that resistance that the two connected objects will be at a different potential from each other.
This fact, not the idea that the equipment grounding (bonding) conductor (EGC) needs ampacity, is why there’s a minimum size for the EGC. It’s also one of the reasons that, in data centers, you find bonding jumpers connected across the joints of metallic raceway.
The NEC answers the “how much conductivity” question in various ways, with a fairly high density of answers in Part V of Article 250. The next term defined in this list is also a clue, as we’ll see in Part 3.
