|  | 8.7 | Planning Structured Cabling: Cabling and Grounding
| 8.7.1 | Causes of ground potential problems
In order to understand the conditions that must be present in order for there to be a problem, assume that the ground wire for building A has a slightly different potential, to the common and hot wires, than the ground wire for building B. In this example, the outer casings of the computer devices in building A have a different potential from the outer casings of the computer equipment located in building B. If a circuit were established that linked the computer devices in building A to those in building B, then electrical current would flow from the negative source to the positive source. Theoretically, in such a situation, if someone were to touch network devices with different ground connections, they would receive a nasty shock. In the example outlined above, can you explain why a person would have to simultaneously touch devices with different grounds for a shock to occur? As this theoretical example demonstrates, when devices with different ground potentials are linked in a circuit, they can produce hazardous shocks. In the real world, however, the chances of any such occurrence as that described above, are very slight, because in most instances a person would have to have extremely long arms to complete the circuit. There are situations however, where such circuits can be created.