System grounding 333 conductors that connects them to the neutral bus, and then the neutral bus connects to ground by virtue of the system grounding electrode. When two or more independent power sources are used in proximity to one another, it is likely that some potential exists between them. To use the (somewhat dubious) pilot analogy again, it is as if we now have a pair of pilots flying low in fog, with no visual reference to each other or the ground. Without something to establish a relationship between the power sources, we do not know what potential may exist between them. Sounds like trouble, right? If a person were to touch the cas- ing of a piece of equipment grounded to one power source and at the same time touch the casing of another piece of equipment grounded to the other source, they might find a dangerous potential exist- ing between them. This is why a bonding conductor is used to create a zero-potential relationship between power sources. Here again the bonding conductor does not carry any appreciable current, but once it is established, all the equipment used on both power sources will have the same zero- potential to ground and to each other. When two power sources are bonded, they must both be connected to a single grounding electrode. There can be only one system ground. When power is supplied to the set by two or more separately derived systems (two generators, or a generator and house power), the systems must be bonded. In the case of bonding a generator to a building's service, the bond must be made to the building's grounding electrode conductor. In the case of two generators, the bonding wire connects from one generator's ground buss to the other's.