Energized conductor is potential hazard and proper precaution need to be followed while handling energised conductor. Whenever a person comes in contact with an energized conductor, he / she becomes a conducting path for the current. In general, the electric current will take the shortest possible path. If a person is touching energized conductors with both hands, or if he is touching an energized conductor with one hand and a grounded object with the other, the current will pass directly through the person’s heart. However, if only one hand is touching an energized conductor, the current travels to ground along the path of least resistance. In this case, the current moves up the arm, down the body, and out through the nearest leg. The current tends to stay on one side of the body, so it is less likely to pass through the heart.
The body is a conductor, which means that current will pass through it when path is formed. The severity of electrical shock depends on how much current passes through the body, duration of the current passing through body, the path that it takes and the physical dimensions of the man.
Although the human body is a conductor, it does offer resistance to the passage of current through it. Different people have different amount of resistance, and different parts of the same body have different resistance values.
The amount of resistance that an individual body offers to the flow of current can vary. Resistance is affected by factors such as individual physiology, a person’s emotional state, and the moisture that may or may not be on a person’s skin.
The amount of current flow passing through a body depends on three factors.
(1) Source voltage
(2) Body resistance along the current path
(3) Current capacity of the source
Thus it is the voltage level and its current capacity which determines the amount of current flowing through the body. This does not mean that high voltage is dangerous rather the source should have enough capacity to flow the required current through human body for shock.
Let us take another example. Suppose there is a source of capacity 10 VA. Assume this source can deliver 5 A current at 2V. If one touch such system then even he will not feel shock as the capacity of source is not enough to flow current more than 0.5 mA required for shock perception (Assuming body resistance to be 1kOhm). Thus we can say that, it is the capacity of source to derive current through human body is responsible for shock. Thus we can’t just say that voltage or current is dangerous though current flowing through the body is responsible for shock.
The effects of current flowing through human body are tabulated below to give a general idea.
|Sr. No||Current magnitude||Physiological effects||Description|
|1||0.5 mA||Threshold of perception||A current at which a person is just able to detect a slight tingling sensation in his hand or finger tips.|
|2||0.5 – 5 mA||Unpleasant to sustain||This is often termed as let go currents. Do not impair the ability of a person holding an energised object to control his muscles and release it.|
|3||5 – 9 mA||Threshold of muscular contraction||These are threshold values of muscular contraction.|
|4||9-25 mA||Muscular contraction||
May be painful and can make it hard or impossible to release energised objects grasped by the hand.