What are the physical differences between shocks by AC
and DC current? Both are dangerous and can be lethal in
high amounts. Learn more here.
Difference between AC and DC CurrentAn AC current is alternating in nature and follows a sine curve. It is continuously changing direction and passing through zero to a maximum positive value and then to a maximum negative value. The voltage of an AC current is a RMS or root mean square value, and the peak or maximum value is 1.4 times the RMS value. It means that a 220 V AC supply is going to 308 Volts before coming down to zero and changing direction.
DC current is direct current and does not change in magnitude, though it can be negative or positive depending on the direction of the circuit. DC current is ideal for electronic circuits whereas AC is ideal for electrical installation and motors, etc.
Effects of an AC or DC Currents on the Human Body
The three basic factors that determine what kind of shock you experience are the amplitude of the current, the duration of the current passing through the body, and the frequency.
Direct Currents actually have zero frequency, as the current is constant. However, there are physiological effects during electrocution no matter what type of current.
The factor deciding the effects of the AC and DC current is the path the current takes through the body. If it is from the hand to the foot, it does not pass through the heart, and then the effects are not so lethal.
However DC current will make a single continuous contraction of the muscles compared to AC current, which will make a series of contractions depending on the frequency it is supplied at. In terms of fatalities, both kill but more milliamps are required of DC current than
AC current at the same voltage.
If the current takes the path from hand to hand thus passing through the heart it can result in fibrillation of the heart. Fibrillation is a condition when all the heart muscles start moving independently in a disorganized manner rather than in a state of coordination. It affects the ability of the heart to pump blood, resulting in brain damage and eventual cardiac arrest.
Either AC or DC currents can cause fibrillation of the heart at high enough levels. This typically takes place at 30 mA of AC (rms, 60 Hz) or 300 – 500 mA of DC. Though both AC and DC currents and shock are lethal, more DC current is required to have the same effect as AC current. For example, if you are being electrocuted or shocked 0.5 to 1.5 milliamps of AC 60 Hz current is required and up to 4 mA of DC current is required. For the let-go threshold in AC a current of 3 to 22 mA is required against 15 to 88 of DC current.
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