Final answer:
The usual resistance between an alarm panel and the ground varies, but when it comes to electrical safety, the lower the resistance, the greater the potential hazard. A person can experience shock with a resistance as low as 3.00 kΩ when wet. Electrical systems use grounding and circuit breakers to manage fault currents and protect against electric shocks.
Step-by-step explanation:
Electrical Safety and Resistance
The resistance between an alarm panel and the ground is an important factor in electrical safety. In regards to appliances and electrical systems, grounding helps to ensure that any fault current gets safely directed into the earth, minimizing the risk of electric shock. An example can be seen when a person experiences a shock from a grounded metal case of an appliance due to a short circuit. If the person is wet, their resistance to the ground can be as low as 3.00 kΩ - a dangerous scenario as this lowers the resistance and increases the potential for a harmful current to pass through the individual.
Another scenario involves a power line carrying 5.00 × 10² A being supported by insulators providing a resistance of 1.00 × 10¹ Ω each, which illustrates the high resistance provided by insulators in preventing electric current from traveling to ground through the tower. When discussing the resistance of the earth/ground wire in an appliance, it is worth noting that even with a low resistance such as 0.200 Ω, a significant enough short circuit current can trigger a circuit breaker designed to protect against currents exceeding 20.0 A.
It is critical to consider the difference between the resistance offered by an individual in various conditions. Dry conditions can provide very high resistance, preventing electric shock, as in the case of a man who does not feel a current through a 120-V AC because he is wearing rubber-soled shoes. Conversely, the presence of moisture greatly lowers this resistance, increasing danger. For instance, a person standing barefoot on wet grass offers a significantly lower resistance of only 4500 Ω, and at 120 V, the current could be hazardous.