Understanding Ground Resistance

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Basic Definitions:

By Ohm’s Law, there will be a current of 100 amperes ** through the fault (from the motor frame to the earth). If you happen to touch the motor frame and are grounded solidly to earth, (say, by standing in a puddle) you could be subjected to 1,000 volts (10 ohms times 100 amperes).

This may be much more than enough to kill you instantly. If however, the earth resistance is less than one ohm, the “shock” you’d get would be under 100 volts (1x100) and you’d probably live to correct the fault. Equipment can also be damaged similarly by over-voltages caused by high-resistance grounding systems.