Both containers must be physically interconnected to eliminate any static electricity which may cause a spark and ignite the flammable liquid vapors. Physically connecting the containers equalizes the difference in the static charge which may be present between the two object. Therefore, a ’bond’ wire between containers during flammable liquid filling operations must be provided, unless a metallic path between them is already present.
Although bonding will eliminate a difference in static potential between
objects, it will not eliminate a difference in potential between these objects and the earth unless one of the containers is grounded.