Electric Safety
Electric Shock and the Human Body
In modern countries, workshops, offices, classrooms or workplaces, it is forbidden to work alone when working with equipment, especially if it utilize the electric main supply or if the voltage is higher then 24 or 25V. If working alone, in the event of an accident, should you receive an electric shock or burns, there would be no-one nearby who could help you.
Voltage such as domestic AC mains voltage or voltage higher than 24V can rise to particular hazards.
The human heart is a muscle and happen to be most susceptible to stimulation at an applied frequency of about 50-60Hz, which happen to be the most used frequency for mains supplies around the world.
DC Voltage above a few volts is dangerous.
The effect of electric shock are a combination of the voltage level applied (amplitude), the current which flows through (into) the body and the time period of the shock itself.
Assuming that an unfortunate person pick up or touch a "Live" Electric circuit, the typical effects on the victim would be:
| Current | Effect on human being |
|---|---|
| 1mA | Tingling. |
| 9mA | Probably able to release the device or circuit. |
| 16mA | Borderline on ability to drop the faulty device. |
| 25mA | Probably unable to release the device to escape further electric shock |
| 16 - 50mA | Pain, possible unconsciousness. Possible problem with heart and respiration functions in the future. |
| >100mA | Ventricular fibrillation (Heart tremor). Respiration paralysis (asphyxia, suffocation), severe shocks and burns and possible death. |
Electric current rise in temperature in material
Accidental heating can be dangerous. Any current passing through any material is subjecting that material to heat due to its resistive losses. Excessive heating will cause fire.
Protection devices
In many countries, legislation to protect humans and assets dictates the use of protection devices to protect peoples, properties and equipment.
To select a disconnection device, several characteristics need to be taken into account:
- The time it will take to disconnect the source.
- From what type of fault (over-current or leakage current) you want to be protected.
- The amplitude of fault current which will trigger the device.
In case of over-current load protection, circuit breakers are utilized to break the circuit supplying a load.
In case of leakage current protection, earth leakage circuit breaker, or ground fault circuit breaker are utilized.
Always equip you workbench with safety device.
