Each of the existing electrical appliances, power tools, as well as electrical equipment, electrical installations pose a certain danger to humans. Of course, she comes out differently. With it, it helps to determine the electrical safety class, which is introduced in relation to each of the electrical devices. We will get acquainted with these classes, their characteristics. Let us consider separately the electrical safety groups not only for equipment, but also for production facilities and personnel.
Norms and Standards
To make the use of various electrical equipment safe, the designers at the design stage solve a number of problems that can minimize and neutralize operational risks for humans. Such a solution may be enhanced insulation of conductive components, protective power offs, separation of electrical circuits, etc.
Depending on the similar measures taken for electrical safety, as well as the design of a particular product, the conditions for its use, a specific electrical safety class is assigned to the device.
When classifying such electrical products, specialists rely on the following state standards:
- GOST 12.2.007.0-75.
- GOST R IEC 536-94.
Main classes
The above standards introduce several classes of electrical safety for devices, instruments, industrial equipment:
In addition to them, there are additional classes of electric tools for electrical safety. We will present and characterize all of them further.
Group 0
What defines this electrical safety class of equipment? In such devices there is only operational isolation from alternating or direct current. In case of its (current) leakage, grounding contact is not provided.
Here, open, non-conductive conductive elements are not connected either to ground or to the protective conductor of the electrical wiring. In the case when such insulation is punched, protection for a person can be provided only by the environment - air, flooring, etc. There are no hazardous voltage indicators on the enclosures of this class of devices.
Such devices can only be used in spaces where there are no conductive grounded elements in the area where people are located, where there are no conditions of increased danger, where unauthorized persons are prohibited.
Therefore, such equipment must be installed only in dry spaces and rooms. If you rely on the recommendations of the International Electric Commission, then the use of class 0 electrical equipment should be completely abandoned. Why?
If the insulation is damaged on the non-conductive elements of the devices, voltage can appear that is dangerous to human health and life. Accordingly, such a threat increases when operating Class 0 equipment in damp, humid rooms.
An example is any appliance in a metal case that is not connected to the ground by the manufacturer - the same electric stove with open heating elements. Another striking example is Soviet heaters equipped with open spirals.
Group 00
What distinguishes this hazard class in electrical safety from the previous one? The conductive case of such a device contains a warning sign. In addition, equipment of class 00 may be used in hazardous spaces and premises. For example, characterized by high humidity.
But at the same time, electrical personnel must be provided with the necessary protective equipment:
- Latex gloves.
- Rubber bots.
- Rubber galoshes.
- Rubber insulating mats, stands and walkways for work.
Of course, before using PPE, workers should be instructed in the proper use of these personal protective equipment.
An example of Class 00 electrical equipment is portable gasoline generators.
Group 000
This class of protection for electrical safety has a number of distinctive features:
- Power line connection through RCD.
- The value of the differential current here cannot be higher than 30 mA.
- The response speed for this class is - no more than 80 ms.
If there is the necessary PPE, then class 00 electrical equipment can be operated in spaces, premises, which belong to the increased electrical hazard group.
Group 0I
The following stands out this class of hand-held electric safety tool. Current-carrying parts of such equipment are insulated, but insulation is already absent on the metal components of the structure. Protection is realized here by mechanical or electrical contact with the PE bus. This ensures equalization of potentials. And also does not allow the formation of electric charges on metal elements when insulation is damaged.
Here, contact with the ground loop will be displayed with a special graphic symbol. According to existing standards, grounding wires have a yellow-green hue.
An example is both stationary and rail-moving devices, but no further than the length of the ground wires. That is, cranes, electric locomotives, transformer substations, etc. Such installations will always be operated only with grounding.
Group I
A prerequisite for this class of tolerance for electrical safety is the presence of both protective grounding and working insulation. As for grounding, it is usually implemented by installing a special plug, where there is a mechanical contact that provides connection to the PE bus.
As for the metal shells of the device (for example, the cases of electric tools, other metal structural elements), they are also connected to the common ground loop.
The main protection here is ordinary isolation. The conductive parts of the device are in contact with the protective conductors of the electrical wiring, which protects them from harmful voltage. After all, protection will work.
An example of equipment of this class can be called almost all existing household appliances and electronics - personal computers, food processors, dishwashers and so on.
Group I +
What is its difference from the previous class? This is a mandatory RCD. Moreover, the conditions for its operation are the same as those given above for class 000.
Equipment of this category is allowed to be used in spaces, premises of increased danger. A typical example of such electrical devices is boilers (storage water heaters), washing machines for installation in bathrooms.
Group II
Now we will determine how the electrical devices of this class differ. This is the presence of a double insulating coating in relation to conductive elements. But the metal components (in particular, the casing) here will not be connected to the common ground loop.
As a result, there will be no special contact for protective grounding on the device plug. Electrical equipment, electrical appliances of this class may be used in rooms where air humidity can reach even 85%.
Sometimes they are divided into two subclasses - equipment with metal shells and completely isolated.
There are quite a few examples of such equipment: hair dryers, trolleybuses, electric drills, vacuum cleaners, street lamps.
Group II +
It is important to highlight that the installation of RCDs is mandatory in the power circuits of such equipment. The connection of metal components to ground loops is not performed here. Therefore, in the electric plugs, the presence of PE contacts is not provided.
Group III
This will mean electrical equipment that is powered only through a voltage-sensing transformer. Therefore, devices of this class will operate on 36 and 48 V (respectively, AC or DC voltage).
Protection is provided by the fact that power is supplied from an ultra-low voltage that is safe for humans. And in the device itself there is no voltage more than it.
This class includes many portable devices powered by rechargeable batteries, as well as devices with a low-voltage external power supply. These include laptops, lights, players, radios and so on. Grounding contact is not provided here in principle.
If the shell is conductive, then its connection with grounding conductors is allowed (but only if it is provided for by the standards for this device). Also, grounding can be present for functional purposes (depending on the purpose of this grounding).
Categories of premises
You can also distinguish the classes of premises for electrical safety:
- Without increased danger. These are spaces with reduced air humidity (up to 45%). There is a ventilation and heating system. Floors are non-conductive (earth, reinforced concrete, earth, etc. are considered to be conductive). If this is a production workshop, then its floors are covered with a dielectric. In such rooms there are no high temperatures, dampness, chemical environments, conductive floors and dust.
- With increased danger. What can be said about this hazard class of electrical safety facilities? Space will be included in the category if it meets at least one of these conditions: damp (air humidity over 75%), conductive dust is constantly present, there is conductive flooring (reinforced concrete, brick, metal, earth), constantly high temperatures (more than 35 ° FROM). Also, these are the rooms where people can simultaneously touch the metal shells of the equipment and the grounded metal structure of the building.
- Particularly dangerous. These are rooms with "special dampness" (in some cases it can reach 100%), spaces in which there is an active chemical or organic environment (which can destroy equipment). Also, premises that fall under any two conditions from the category of “with increased danger” are considered particularly dangerous.
Classes for staff
We will also get acquainted with the electrical safety classes of personnel:
- The first group. Assigned to workers who do not work on electrical installations and do not serve them.
- The second group. Assigned to electrotechnological personnel working on electrical equipment. It is possible to work on electrical installations, but under supervision and without connection.
- The third group. Assigned to electrical personnel servicing electrical equipment. Gives the right to independently connect, inspect devices with voltages up to 1000 V.
- The fourth group. The specialist can work with installations in which the voltage exceeds 1000 V.
- Fifth group. Maximum liability is assumed. A specialist can not only work with all existing electrical devices, but also supervise the work on them, and be responsible for the field of electrical engineering.
We analyzed the main classes of electrical safety, as well as well-known subcategories, their characteristics. Electrical safety groups have also been introduced for personnel, premises, and production spaces.