If you are working on electric circuits, there is often possibility of receiving an electric shock by touching the "live" conductors when the power is on. The shock is a sudden involuntary contraction of the muscles, with a feeling of pain, caused by current through the body. If severe enough, the shock can be fatal. Safety first, therefore, should always be the rule.
The greatest shock hazard is from high-voltage circuits that can supply appreciable amount of power. The resistance of the human, body is also an important factor. If you hold a conducting wire in each hand, the resistance conductor tighter lowers the resistance. If you hold only one conductor, your resistance is much higher. It follow that the higher the body resistance, the smaller the current that can flow through you.
Note that it is current through the body, not through the circuit, which causes the electric shock. This is why high-voltage circuits are most important, since sufficient potential difference can produce a dangerous amount of current through the relatively high resistance of the body. For instance, 500 V across a body resistance of 25,000 Ω produces 0.02 A, or 20 mA, which can be fatal. As little as 10 µA through the body can cause an electric shock. In an experiment on electric shock to determine the current at which a person could release the live conductor, this value of "let-go" current was about 9 mA for men and 6 mA for women.
In high voltage, the other important considration in how dangerous the shock can be is the amount of power the source can supply. The current of 0.02 A through 25,000 Ω means the body resistance dissipates 10 W. If the source cannot supply 10 W, its output voltage drops with the excessive current load. Then the current is reduced to the amount corresponding to how much power the source can produce.
The greatest danger is form a source having an output of more than about 30 V with enough power to maintain the load current through the body when it is connected across the applied voltage. In general, components that can supply high power are physically big because of the need for dissipating.
The greatest shock hazard is from high-voltage circuits that can supply appreciable amount of power. The resistance of the human, body is also an important factor. If you hold a conducting wire in each hand, the resistance conductor tighter lowers the resistance. If you hold only one conductor, your resistance is much higher. It follow that the higher the body resistance, the smaller the current that can flow through you.
Note that it is current through the body, not through the circuit, which causes the electric shock. This is why high-voltage circuits are most important, since sufficient potential difference can produce a dangerous amount of current through the relatively high resistance of the body. For instance, 500 V across a body resistance of 25,000 Ω produces 0.02 A, or 20 mA, which can be fatal. As little as 10 µA through the body can cause an electric shock. In an experiment on electric shock to determine the current at which a person could release the live conductor, this value of "let-go" current was about 9 mA for men and 6 mA for women.
In high voltage, the other important considration in how dangerous the shock can be is the amount of power the source can supply. The current of 0.02 A through 25,000 Ω means the body resistance dissipates 10 W. If the source cannot supply 10 W, its output voltage drops with the excessive current load. Then the current is reduced to the amount corresponding to how much power the source can produce.
The greatest danger is form a source having an output of more than about 30 V with enough power to maintain the load current through the body when it is connected across the applied voltage. In general, components that can supply high power are physically big because of the need for dissipating.
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