Thank you for your question regarding Step Potentials (Voltage) and bonding, it is our pleasure to help.
Step and Touch Potentials are hazardous electrical voltages that form when electrical energy enters the earth, typically (but not exclusively) during fault conditions. Let’s take for example a high-voltage tower with a cellular communications site (cell site) installed under it. The insulators on the tower get dirty over time and must be washed and maintained to prevent unintentional arcing as the build-up of dirt eventually forms a conductive path to ground. If this path is allowed to from, the electrical energy in the lines will arc over to the tower and down into the earth through the footings. Note: birds landing on the insulators can do the same thing.
The massive amount of electrical energy will enter the earth and saturate the surrounding soil charging everything touching in the immediate area, including the cell site. This is called a Ground Potential Rise or GPR event. The further one is away from the tower, the less of the charge they will encounter. You could imagine a pebble being dropped into a still pond, the waves will propagate away from the pebble getting smaller and smaller as the distance increases. This is similar to an electrical fault, the energy will travel out and away from the tower decreasing the potential with distance. Step voltage is the difference in voltage a person could experience between their front leg and their back leg when walking near the tower. In other words, if you are walking towards the tower during a fault, your front leg might be at 1,000-volts, and your back leg at 750-volts, giving you a 250-volt difference between your two legs (these numbers are for example only). This 250-volt differential can be hazardous to your health.
Touch Potential is the difference between your hands and your feet should you be touching a metal object when the fault occurs. For more information please follow the link below:
The reason everything must be bonded, is to prevent hazardous differences in potential from forming. It would take quite a bit to explain all the reasons why bonding is important, but not only does proper bonding ensure that your circuit-breakers will work right, but it is the “Law of the Land”. Needless to say, you are far safer being in at a site that is properly bonded than one that does not have all the metallic objects tied together via a good grounding system.
We hope you have found this information useful. If you should have any further questions, please do not hesitate to call one of our engineers and they will happily answer your questions free of charge.
The Engineering Team at E&S Grounding Solutions
Photo credit: http://www.flickr.com/photos/mamchenkov/2856984903/sizes/o/in/photostream/