The fundamental concept of Electrical Power Transmission always gives rise to a chronic confusion faced by numerous students and professionals. Namely, the difference of intensity between AC and DC, and the hazardous threats posed by both.
In order to learn about this ambiguity, we first need to be clear about the basic difference between AC and DC.
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The difference between AC and DC:
AC, known as alternating current, is the current which reverses its direction over a time period. Alternating current flows in the form of a sine wave. The number of cycles completed in a second is known as frequency.
The common frequency used globally is 50 Hz, meaning that the current completes 50 cycles in one second.
DC, or direct current, is the current which does not reverse its direction and flow in a straight path while the polarity remains constant. Since DC does not flow in sinusoids nor change direction, it does not have a frequency.
What causes an Electric Shock? Current or Voltage?
The root cause of an electric shock is always current, not voltage. An electric current can be defined as the flow of charges from a higher potential point to a lower potential point.
Nevertheless, voltage can positively determine the magnitude of current, which can ultimately determine the magnitude of an electric shock.
Why does the human body feel an Electric Shock?
One thing we should know is that every human body possesses an internal resistance to electric current which varies throughout the body. The skin having the most resistance of about 100,000 ohms while the internal body having at least 300–500 ohms.
This internal resistance can cause energy from the current to dissipate, resulting in a severe heating effect or even burns. Once the tissue breakdown of the skin occurs, the body acts as a perfect conductor for the current as our muscles, blood and organs contain many ions to propagate.
Some important factors:
Sweaty or wet conditions cause the skin to significantly reduce resistance, resulting in increased intensity of electric shock as more current passes through it.
Some values of skin resistance can be seen Here.
Human body fat has a high resistance. So, for two people having different body fats, the person with the higher percentage of body fat will experience a less severe shock as compared to the person with lower fat.
AC can cause stimulation of sweat glands and induce sweating thus lowering our body resistance which will consequently increase the shock current.
The time duration of electric shock is also important. The severity of the injuries increases with the duration of time. Even a small current of 0.4 mA can be painful if held on for too long. Fibrillation can occur within 0.2 seconds at 500 mA, while it can take 0.5 seconds at 75 mA.
Let’s talk about AC vs DC comprehensively now.
RMS and Peak Values
Since AC current and voltage are represented in the form of a sine wave, hence it possesses a minimum and maximum peak. The current/voltage values obtained at these points are the Peak values or the highest values achieved in the process.
As for RMS values (root mean squared values), these are the values of AC current and voltage which produce the same level of heating effect as DC.
Since DC does not have a sinusoidal waveform, it will not have any RMS value, and only a constant peak value will be maintained.
Same level of AC and DC power:
Let’s suppose we have a 220 Vrms AC and a 220 V DC, what do you think will be more dangerous?
Well, for 220 V being a RMS value for AC, its peak value will be 311 V, hence it will be having a higher value of current at some point.
One thing should be kept in mind that it’s not the voltage but the current that causes an electric shock. Apart from voltage, current will also be dependent on the body resistance.
Therefore, the value of resistance matters more than the same levels of AC and DC power. The lower the resistance of the current path, the greater will be the electric shock.
The hazardous effects of AC and DC
We can observe various damaging effects based on different DC and AC values employed to a human body. Such effects can range from slight current sensation to serious tissue burns and heart failures. One can find specified AC and DC values along with their effects in a tabular form in our detailed article.
The effect of frequency
A 50 or 60 Hz AC current can be much more fatal than a 2000 or 4000 Hz one because the electrical pulses can effectively stimulate our body’s muscles at this frequency. For reference, a 50 mA AC current at 50 Hz will be sufficient to cause a heart failure while a 150 mA DC signal will be required to produce the same effect.
DC and AC both can prove to be lethal. However, since AC has the potential to influence internal body damages at much small magnitudes than DC, make it far more lethal.
In conclusion, we would like to stress that electricity should never be taken lightly. Avoiding bare contact with electricity is the least we can do. It is also important for workers to have relevant PPE’s such as rubber boots and gloves while handling Electrical equipment.
Another hazard is an Arc Flash event in an electrical system. That is why electrical safety and prevention techniques are crucial for any commercial or industrial facility.
Let us know if you have any queries regarding this topic and do provide us with your feedback in the comments.
AllumiaX, LLC is one of the leading providers of Power System Studies in the northwest. Our matchless services and expertise focus on providing adequate analysis on Arc Flash, Transient Stability, Load Flow, Snubber Circuit, Short Circuit, Coordination, Ground Grid, and Power Quality.
About The Author
Abdur Rehman is a professional electrical engineer with more than eight years of experience working with equipment from 208V to 115kV in both the Utility and Industrial & Commercial space. He has a particular focus on Power Systems Protection & Engineering Studies.
Abdur Rehman is the CEO and co-founder of allumiax.com and creator of GeneralPAC by AllumiaX. He has been actively involved in various roles in the IEEE Seattle Section, IEEE PES Seattle, IEEE Region 6, and IEEE MGA.