Class of protection against electric shock
The classification of devices according to the degree of protection of the user against electric shock implies a system of designation to inform the user. These classes are defined by the GOST R IEC 61140-2000 standard and reflect the way in which protection against electric shock is carried out in each specific case.
Protection classes higher than «0» have the corresponding icons, and grounding is marked with its own separate icon at the point where the potential equalization wire is connected (this wire is usually yellow-green in color, it is connected to the corresponding contact of the contact , chandelier, etc.).
Class «0»
Class 0 electrical appliances do not have special protective equipment against electric shock for the user. The main working isolation is the only protective element. Exposed conductive non-conductive parts of the equipment are connected neither to the protective conductor of the wiring nor to ground. If the main insulation breaks, then only the environment will provide protection — air, flooring, etc. There is no indication of dangerous voltage on the enclosure.
The use of such devices is permissible only in those premises where there are no grounded conductive objects in the working area of people, where there are no conditions of increased danger and where the access of unauthorized persons is limited. However, the IEC does not recommend Class 0 devices for release according to PUE (point 6.1.14.) lighting fixtures of this class can be used even in "dangerous" premises, but always in accordance with a number of requirements described in the PUE.
A vivid example of such a device is a Soviet heater with an open spiral. It is best to avoid using such devices as much as possible and decommission them as soon as possible. By the way, in many developed countries devices of class «0» are recognized as dangerous.
Class «00»
The only difference from class «0» is that there is an indication of the presence of dangerous voltage on the conductive body of the device. It can be used even in wet areas, but personnel must be trained and equipped with personal protective equipment. Mobile gasoline power plants are an example of such equipment.
Class «000»
Like class «00», however, there is a protective device in case the difference in currents in the supply wires is exceeded by more than 30 mA — the interruption occurs after 0.08 seconds. Persons working with the equipment must have personal protective equipment.
Class «0I»
The device has functional insulation, non-conductive conductive parts are not insulated, but they are connected to the protective earth conductor with a special conductor, or are in mechanical contact with the earth loop. The point of contact with the ground loop is marked with a special symbol.
An example of an installation is a stationary device or a device that moves on rails no longer than the length of the ground wire, for example, a crane, a transformer substation, an electric locomotive, etc. Such installations are always used only with earthing.
Class «I»
The conductive parts of the appliance are earthed by means of a plug that has a special contact with the outlet, which in turn has an earthing contact. If there is no ground, then the class becomes similar to class «0».
The basic protection is provided by simple insulation, and the conductive parts of the equipment are in contact with the protective conductor of the wiring, thus protected from dangerous voltages getting on them — the protection will work. Equipment that is used with a flex cable is protected by a yellow-green wire that goes into the flex cable.
Examples of equipment with protection class «I» — dishwasher, personal computer, food processor.
Class «I +»
As with class «I», earthing through the conductor in the cable, through the contact of the plug and the socket, but there is also RCD… If the ground is suddenly disconnected, the device will become similar in protection class to a device with protection class «000»
Class «II»
Equipment of this class has double reinforced insulation. The body is not grounded here for protection purposes and there is no dedicated grounding pin on the plug. The environment does not serve as a means of protection. All protection is provided by special insulation. At humidity above 85%, the use of the equipment may be restricted if enclosure protection class below IP65... Designation — two concentric squares.
Example of devices: TV, hairdryer, trolley, vacuum cleaner, street lamp on a pole, drill.For safe operation, all electrical equipment of the trolleybus, including low voltage, must be made in accordance with protection class II. European-made trolleybuses have electrically conductive tires for wheels, which significantly increases safety.
Sometimes, if necessary, Class II equipment may have protective resistance on the input terminals. For additional safety, equipment of this class can be equipped with means for monitoring the operation of protective circuits, which are isolated from the surface and are an integral part of the device.
Distinguish equipment of class «II» with a metal shell and fully insulated. If the sheath is metal, then it is allowed to have a means of connecting a shielded yellow-green wire (regulated by the specific equipment standard). It is allowed to connect the ground wire not only for the purpose of protection, but also for other purposes, if this is required by the standard for this equipment.
Class «II +»
Double reinforced insulation plus RCD. You do not need to ground the housing or the plug. No ground contact is provided. The notation is concentric squares with a plus sign inside.
Class «III»
In equipment of this class, protection against electric shock is provided by the fact that the power supply is carried out at an extremely low voltage, which is safe, and there is no voltage higher than a safe voltage in the device itself. This means 36V AC or 42V DC. Designation — Roman numeral 3 in a square.
These devices include portable battery powered devices, low voltage externally powered devices (flashlights, laptops, radios, players). A ground contact is not normally provided.
If the sheath is conductive, then it is allowed to connect it to a ground wire, if this is due to the requirements of the standard for this device. Grounding may also be present for functional purposes, again depending on the purpose of the grounding (not for protection purposes).