2. Electrical Safety

If the voltage applied to the skin exceeds 240 v it

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Unformatted text preview: The danger of the foot- to- foot electric shock to the person depends on the difference of the electric potentials between the feet. The numerical values in Figure 2- 6 serve only as guidelines. The big idea is that the danger of the electric shock due to foot- to- foot connection to the ground is determined by the potential difference between the feet, which depends on the location of the person and on the distance between the feet. The safest behavior is either stand on one foot, keep both feet very close to each other, or run (so that only one foot touches the ground at any moment); if this is not practical, better walk with short steps than long strides. This strategy also applies to electric potentials on the ground caused by a fallen electric wire. <Sidebar> The electric potentials created on the surface of the ground by a thunderbolt or a fallen high- voltage wire may cause a lethal electric shock due to the foot- to- foot connection. The best survival strategy is to minimize the potential difference between the feet. A less probable (but not impossible) case is when a “hot” wire falls on your car so that the car body is at high voltage. Again, the strategy is to avoid potential differences between parts of your body: if you need to get out of the car, jump with both feet (do not step on the ground with one foot while the other touches the car). © 2013 Alexander Ganago Page 15 of 28 Last printed 2013- 07- 07 12:28 AM File: 2013 EEW 1- 02 Electrical safety.docx Engineering in the Electrical World (EEW) Part 1 Unit 2: Electrical safety Household wiring and Ground Fault Circuit Interrupter (GFCI) To build a complete circuit, which connects the source of electric power to the load, two wires suffice, as shown in Figure 2- 7. Figure 2- 7. Two wires are enough to connect an electric appliance to the power grid. The colors are in accordance with the National Electric Code (NEC). One of the wires is connected to the ground, in order to ensure the safe reference point at zero potential. The other wire is “hot” or live; its electric potential is definitely not zero: the exact value is determined by the power source, shown as a voltage source in Figure 2- 7. The difference of electric potentials between the two terminals of the power supply (and the two terminals of the power o...
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This note was uploaded on 12/06/2013 for the course EECS 314 taught by Professor Ganago during the Fall '07 term at University of Michigan.

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