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This article is the first in a 12-part series on the differences between grounding and bonding.
Article 250 provides requirements for the grounding and bonding of electrical installations. It covers two different concepts:
- “Grounding” is the connection to the earth. The grounding requirements provide a path to the earth to reduce overvoltage from lightning strikes, line surges, or unintentional contact by higher‑voltage lines [Sec. 250.4(A)(1)].
Failure to ground metal parts to earth can result in millions of volts induced on those metal parts. This energy seeks a way to the earth within the building, taking whatever paths are available (not just “the one with least resistance”, see Kirchhoff’s Law of Parallel Circuits). This can easily result in a fire and/or electric shock either by direct contact or from a flashover.
- “Bonding” is mechanically connecting electrically conductive components to ensure electrical conductivity between metal parts [Art. 100]. The bonding requirements establish a low‑impedance fault current path back to the source of the electrical supply so overcurrent protective devices (OCPDs) operate if there’s a ground fault [Sec. 250.4(A)(3)].
These two systems overlap, but each serves a different purpose. You need them in both solidly grounded systems [Sec. 250.4(A)] and ungrounded systems [Sec. 250.4(B)].
