The following is a comment from a Linked-In discussion concerning grounding and bonding of gas piping in buildings. It is a critical piece to understand when attempting to differentiate between GROUNDING and BONDING. The difficulty arises because bonding, in most cases, achieves at least some degree of grounding as well, but the intent, methods, and applicable conductors can be significantly different.

This comment, posted by Aron Kumar, explains the difference about as well as it can be:

Bonding is the physical connection of the conductive materials of equipment and metal objects to the ground reference point in order to prevent the generation of voltage potentials between conductive materials. This has nothing to do with making a gas piping system part of the grounding grid (which it is not to be part of, as in using gas piping for grounding purposes) but has everything to do with attempting to establish a safe, zero voltage potential between conductive materials. Bonding also provides lightning protection by preventing (hopefully) the sudden increase of voltage on one conductive material (metal gas supply, CSST, cable TV, telephone cable, etc.) as opposed to another conductive material. The differential voltage between these materials, circuits, results in damage to sensitive devices, and in the case of CSST can result in blowout with arcing and a fire.

The grounding requirements for lightning protection are not the same as for electrical bonding or as for the NEC electrical grounding requirements. Typical electrical grounding and bonding in the NEC is for residential/commercial voltages at a frequency of 60 HZ, which travel within the conductive material. The grounding and bonding requirements for lightning protection are for significantly higher voltages at high frequencies that travel along the exterior surface of the material.

A safe grounding and bonding system must consider the voltage potential, conductive ground return, ground voltage differences, single point grounding, lightning protection, electrical safety, and lightning protection. The grounding and bonding conductor sizes and materials are not the same for typical NEC requirements for residential/commercial systems and for lightning protection. An example is the fact that rebar in concrete is now allowed by the NEC to be used as a primary grounding point for the electrical system. However, lightning protection requires the primary grounding point be located outside the building and via driven grounding rods, and that all grounding rods be connected (bonded) to each other, and that all conductive materials/circuits that can be exposed to lightning (such as a metal gas pipe) be bonded to the grounding point.