Which is dangerous current or voltage 1

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Effect of the electric current on humans

Electric current is dangerous to humans and animals for various reasons. All fluids in the human body conduct electricity.


Almost all organs function based on electrical impulses from the brain. These impulses with a strength of about 50mV control our movements and organs.

These currents can be measured with various electrical devices used in medicine. E.g. the EKG (electrocardiogram) with which the activity of the heart is measured. The heart also works with electrical currents which it generates itself.

Currents coming from outside (external currents) can influence the functions of organs.

The graphic below shows the range of effects of 50 Hz alternating current on adults.

Image 1

Source: Electrical engineering expertise; 22nd edition 1999; Europa Publishing House


If a current flows through the human body, the muscles cramp if the current coming from the outside is much larger than the body's own. (Image 1 + table) Now you are no longer able to let go of the point of contact. For example, if alternating current flows through the heart, the heart tries to follow the faster and stronger impulses from outside (e.g. with 50 Hz mains voltage, the heart would beat 50 times per second). It can too Cardiac arrhythmias and ventricular fibrillation come.

As a result, the heart stops working and cardiovascular arrest occurs. Because of the Lack of oxygen it's coming after a short time to a Damage to the brain. This leads to death in the further course.

The amount of current is decisive for the consequences of an electrical accidentthat flows through the body when touched, the duration of exposure to the body and the way the current takes over the body. It is known from experience that a stream of 50mA lethal can be when it flows over the heart.

Current strengths from 50mA are life-threatening.
The risk increases with higher amperage and longer exposure time
.

picture 2

The current flowing through the body, in turn, depends on the voltage and resistance of the body. This Body resistance R.K is made up of the internal resistance of the body (the Internal body resistance R.Ki) and the Contact resistances R.ü1 and Rü2 at the point of entry and exit. (Picture 2)


The contact resistances depend on external conditions. Dry skin and dry clothing have a high resistance. In the case of moisture, e.g. sweat or wet ground, the transition resistance is low.


Example:


With a current of 50mA through the human body and a body resistance RKfrom the equivalent circuit with RKi and Rü 1000 Ω is assumed, the life-threatening voltage U therefore begins at:


U = RK & middot I

U = 1000 Ω * 50mA

U = 50V

AC voltages over 50V are life-threatening (for animals already 25V).
DC voltages over 120V are life-threatening (60V for animals).
Alternating current with a frequency of 50Hz is more dangerous than direct current because ventricular fibrillation can already occur at this frequency.


Due to the chemical effect of the current, the blood can be electrolytically destroyed, especially if it is exposed to it for a long time. This leads to severe symptoms of intoxication. Such sequelae can only occur after a few days. For this reason, you should always consult a doctor after a voltage accident, even if there are no signs at first.


Due to the risk of accidents, working on live parts is prohibited!

With operating voltages above 50V AC or 120V DC, work on parts that are live is only permitted if these parts cannot be de-energized for important reasons (e.g. major economic damage due to a longer power failure). Such work may only be carried out by qualified electricians with additional training, but not by trainees (DIN VDE 0105).