Classification of Devices Into Protection Classes

Classification Of Devices Into Protection Classes

All equipment connected to supply networks provided by power companies belong to one of three protection classes.

Protection class 1 - Protective grounding







This protection type is used for devices with housings manufactured from electrically conductive material. The housing is connected to the protective conductor (PE - protective earth) on the electrical system, which results in a protective ground and guarantees an equal potential between the housing and the protective conductor. Working voltages are discharged to ground or a shared reference potential via the protective conductor. The ground symbol is used to identify these devices. Typical protection class 1 devices include household appliances such as cookers and toasters, etc.

Protection class 2 - Total insulation







Devices from protection class 2 have basic insulation and additional insulation. If there is contact between an active conductor and the inner sheath, no voltage is present at the housing. Most devices from protection class 2 have plastic housings and no protective conductor connection. The device identification symbol indicates a double housing.

Protection class 3 - Safety extra-low voltage







SELV - Safety extra-low voltage
The safety extra-low voltage is solely a protective measure. The operating voltage of the devices is below the minimum contact voltage of 50 V AC or 120 V DC permitted for people. These include children's toys and 12-volt halogen lamps, for example. The devices must be fitted with a protective isolator. In order for the isolator to work effectively, there must be no connections to a reference potential. The 12-volt vehicle electrical system does not fulfil this requirement because the 12 V negative terminal is connected to the body. Battery-operated devices such as pocket lamps or mobile phones fulfil this requirement without the need for further technical modifications.

FELV - Functional extra-low voltage
The functional extra-low voltage (FELV) is not an independent protective measure. In the same way as the safety extra-low voltage, the operating voltage is less than the minimum permitted values but is solely functional. Devices with a functional extra-low voltage do not fulfil other requirements for dielectric strength, for example. Examples include different control systems and even the 12-volt electrical system on motor vehicles.

The currents that flow in the 12-volt vehicle electrical system are immensely high, but cannot flow through a person due to the comparably high resistance of the human body. In the case of direct, full contact (hand-hand) with the 12-volt battery terminals, the maximum current is a mere 12 mA (12 V/1,000 ohms). The secondary effects (burns from electric arcing, mental shock) represent a danger, however.