Electrical engineering - Basics Page 38

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6. Safety regulations, protection types, safety measures according to DIN/VDE and UVV VBG 4

Under point 1. (introduction into electrical engineering) different effects of electric current had been discussed.
The most common reasons for accidents with electric current are lack of knowledge, negligence and carelessness. This is because human beings mostly are only able to recognise the effects of electric current with their senses and not the causes (the electric current itself).
Statistics and research studies that had been conducted by trade/professional associations prove that only a small part of the accidents with electric current had been caused by defective electrical installations or devices.

This means that in order to avoid accidents it is necessary that

6.1 Dangers of electric current

If a human being touches an electric conductor through which electric current is flowing then this current will also flow through his/her body since the human body also conducts electric current. In such a case, the applied voltage and the total resistance of the body determine the size of the occurring amperage. The total resistance depends on:
Humidity strongly reduces the transition resistance. The amperage is increasing with a decreasing total resistance. For this reason, especially in humid rooms where the transition resistance is usually very small the danger is particularly high.

International safety regulations specify that human beings can only be exposed for a very short period of time:
If these limits are exceeded, electric current can have the following dangerous effects:
  1. An electric current that flows through a human body can have a very negative effect on important body functions. As a result, e.g. muscle cramping, heart flutter and cardiac arrest can occur.

  2. If the human body comes in contact with very high amperages, the electric heat effect causes burns, especially at the points where the current enters and leaves the body.

  3. If an electric current flows for a longer period of time through a human body, the body fluids (among other things the blood) are being decomposed by electrolytic processes. As a result intoxications can occur which sometimes break out with a time delay of several days. For this reason, a medical examination is absolutely necessary after accidents with electric current.

  4. Accidents with electric current very often cause so called "secondary accidents". An example for a secondary accident would e.g. be if a service technician gets an electric shock and is reacting uncontrolled and in panic. Because of this uncontrolled wrong reaction he falls off a ladder or hurts himself with the machine he was working with, etc....


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