Equipotential is a complex word that simply means equalizing electrical potential. Equipotential bonding is the process of making an electrical connection between the grounding electrode and any metal conductor—pipes, plumbing, flues, etc.—that may be exposed to a lightning strike and become a conductive path for lightning energy. Currently, in the United States, the National Electrical Code does not require equipotential bonding for all metal systems in the house. The NEC does require bonding of major metal systems, such as water piping, structural metal beams, and communications lines.
In Europe, equipotential bonding for the entire building and all appliances is the norm. According to Source IEC Session 20 – Earthing/Grounding Regulations:
“Full equipotential bonding is achieved by connecting not only the housings of the electrical equipment into the equipotential bonding, but also all other accessible, conductive structural parts such as building construction, metal containers, piping, etc. Extraneous conductive parts which do not belong to the structure or installation of the system (e.g. door frames, window frames) need not be incorporated into the equipotential bonding. This also applies to housings if their method of fixing provides reliable contact with structural parts for piping already involved in equipotential bonding. The connections for equipotential bonding must be reliable, e.g. using secured screw terminals."
By effectively connecting all metal systems in the house together to the building’s electrical ground, the chances of electrical arcing caused by unintended voltage surges from lightning or transformer failures are significantly reduced or eliminated. Areas of the United States and Canada that require bonding of mechanical and electrical systems have no history of damage to CSST as a result of lightning. Perhaps someday, equipotential bonding will be part of building codes in the United States. Until then, installing CSST piping with enhanced lighting protection and bonding as required by local codes offers optimum protection against the effects of indirect lighting strikes.