NFPA 12 2015 edition - Standard on Carbon Dioxide Extinguishing Systems
4.2.1* Carbon Dioxide fire-extinguishing systems protecting areas where explosive atmospheres could exist shall utilize metal nozzles, and the entire system shall be grounded.
4.2.1 The discharge of liquid carbon dioxide is known to produce electrostatic charges that, under certain conditions, could create a spark. see (NFPA 77)
NFPA 77 2014 edition - Recommended Practice For Static Electricity
188.8.131.52 Where wire conductors are used, the minimum size of the bonding or grounding wire is dictated by mechanical strength, not by its current-carrying capacity. Stranded or braided wires should be used for bonding wires that will be connected and disconnected frequently. (see Annex G for additional information)
So my question is how do you determine the proper wire size based on mechanical strength and why is the method of mechanical strength used over current-carrying capacity?