Measures to ensure electrical safety depend on the purpose of the room in which the electrical installation is located, and on the nature of the room. According to the purpose, specialized premises with electrical installations and premises for other purposes (industrial, household, service, trade, etc.) are distinguished.

State atmospheric air and other factors environment may increase or decrease the risk of injury to people electric shock. So, for example, dampness, conductive dust, caustic vapors and gases, heat have a destructive effect on the insulation of electrical equipment, leading to a decrease in the resistance of the human body.

The risk of electric shock also increases in the presence of conductive floors and metal grounded objects close to electrical equipment that contribute to the creation electrical circuit through the human body.

According to the degree of danger of electric shock to people, all premises of electrical installations are divided into three classes: without increased danger, with increased danger and especially dangerous.

Premises with electrical installations- these are such premises or fenced off parts of the premises in which the operated electrical equipment is installed and which are accessible only to personnel with necessary qualifications and .

Premises with electrical installations are characterized, as a rule, by conditions that differ from normal, elevated temperature, humidity and large quantity metal equipment connected to earth. All this creates an increased risk of electric shock. In the following classification of premises is given: dry, damp, damp, especially damp, hot and dusty.

Dry rooms are called rooms in which the relative humidity of the air does not exceed 60%.

Wet rooms are called rooms in which vapors and condensing moisture are released only briefly in small quantities, and the relative humidity of the air is more than 60%, but does not exceed 75%.

Damp rooms are rooms in which the relative humidity of the air exceeds 75% for a long time.

Particularly damp areas are called rooms in which the relative humidity of the air is close to 100% (ceilings, walls, floors and objects in the room are covered with moisture).

Hot rooms called rooms in which, under the influence of various thermal radiations, the temperature exceeds constantly or periodically (more than a day) 35 ° C.

dusty rooms they are rooms in which, according to production conditions, process dust is released in such an amount that it can settle on wires, penetrate machines, apparatus, etc. Dusty rooms are divided into rooms with conductive dust and rooms with non-conductive dust. In addition, there are rooms with a chemically active or organic environment, where aggressive vapors, gases, liquids are constantly or for a long time, deposits or mold are formed that destroy the insulation and current-carrying parts of electrical equipment.

Considering these indications, premises are divided into three groups according to the degree of danger of electric shock.

Premises without increased danger, in which there are no conditions that create an increased or special danger.

An example of such premises can serve as housing rooms, offices, laboratories, some industrial premises (assembly shops of watch and instrument factories).

Premises with increased danger, which are characterized by the presence of one of following conditions that create an increased danger: dampness or conductive dust, conductive floors (metal, earthen, reinforced concrete, brick, etc.), high temperature, the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological apparatuses, mechanisms, on the one hand, and to the metal cases of electrical equipment, on the other hand.

Examples of such premises are stairwells various buildings with conveying hearths, various workshops, mill rooms, hot shops, workshops with electrified machines, where there is always the possibility of simultaneously touching the motor housing and the machine, etc.

Particularly dangerous premises, which are characterized by the presence of one of the following conditions that create a special danger: special dampness, chemically active or organic environment, simultaneously two or more conditions of increased danger.

An example of such a room is most industrial premises, including all machine-building and metallurgical plants, power plants and chemical plants, electroplating shops, etc.

With regard to the danger of electric shock, the territories where outdoor electrical installations are located are equated to especially dangerous premises.

WORKBOOK

ON THE SUBJECT "HEALTH AND SAFETY"

Developer: teacher Klimova S.N.

2010

annotation

The study of the proposed questions activates the mental activity of students, develops independence.

Use at work workbook can be teachers of special disciplines, masters of industrial training, students in preparation for lessons on the proposed material.

1. Classification of premises for electrical safety

pp.4-6.

2. Tests on the topic "Classification of premises for electrical safety" p. 7-13.

3. Safetyworkwith electrical installations

pp. 14-20.

. 4.Safety tests underworkin existing electrical installations

pp. 21-24.

5. Traumatism. Rendering of the 1st medical aid.

Pages 25-31.

6. Tests on the topic

Pages 32-36.

7. First aid kit universal

Page 37.

8. Public resuscitation techniques.

pp.38-43.

9. Questions for self-control

Page 44.

10. Combustion and properties of substances that characterize their fire safety. Basic concepts.

Page 45-56.

11. Questions for self-control and mutual control

Page 57-58.

Classification of premises for electrical safety

Electrical rooms are called rooms or fenced off, for example with grids, parts of the room, accessible only to qualified service personnel, in which electrical installations are located.

Dry rooms are called rooms in which the relative humidity does not exceed 60%.

Wet rooms are rooms in which steam or condensing moisture is released only briefly in small quantities, and the relative humidity of the air is more than 60%, but does not exceed 75%.

Damp rooms rooms where the relative humidity of the air exceeds 75% for a long time are called.

especially raw premises rooms are called rooms in which the relative humidity of the air is close to 100% (the ceiling, walls, floor and objects in the room are covered with moisture).

Hot rooms rooms are called rooms in which, under the influence of thermal radiation, the temperature constantly or periodically (more than 1 day) exceeds + 35 ° C (for example, rooms with dryers, drying and roasting furnaces, boiler rooms, etc.).

dusty rooms rooms are called in which, according to the conditions of production, process dust is released in such an amount that it can settle on wires, penetrate inside machines, apparatus, etc.

Dusty rooms are divided into rooms with conductive dust and rooms with non-conductive dust.

Premises with a chemically active or organic environment are rooms in which aggressive vapors, gases, liquids are constantly or for a long time, deposits or mold are formed that destroy the insulation and current-carrying parts of electrical equipment.

According to the risk of explosion or fire, the premises are explosive (six classes - B-I, B-Ia, c, d, B-II and B-IIa) and fire hazardous (four classes - P-I, P-II, P-IIIa, P-III).

According to electrical safety conditions, electrical installations are divided into installations up to 1000V and installations above 1000V, operating and inactive.

With regard to the danger of electric shock to people, there are:

Premises without increased danger , in which there are no conditions that create an increased or special danger.

Premises with increased danger awn, characterized by the presence in them of one of the following conditions that create an increased danger:

a) dampness or conductive dust (relative humidity exceeds 75%);

b) conductive floors (metal, earthen, reinforced concrete, brick, etc.);

c) high temperature (more than 35◦С);

d) the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological apparatus, mechanisms, etc., on the one hand, and to the metal cases of electrical equipment, on the other.

3. Particularly dangerous premises , characterized by the presence of one of the following conditions that create a particular hazard:

a) special dampness;

b) chemically active or organic environment;

c) simultaneously two or more conditions of increased danger.

4. Territory for outdoor electrical installations. With regard to the danger of electric shock to people, these territories are equated to especially dangerous premises.

Characteristics of residential premises

and outbuildings

Tests on the topic "Classification of premises for electrical safety"

In accordance with the PUE, according to the degree of danger of electric shock to people, industrial premises are divided into:

High risk areas.

conductive dust;

conductive floors (metal, earth, etc.);

high temperature (more than 35ºС);

relative humidity over 75%;

the possibility of a person simultaneously touching the metal structures of buildings, technological equipment connected to the ground, on the one hand, and to the metal cases of electrical equipment, on the other hand.

The premises are especially dangerous.

They are characterized by the presence of one of the following conditions:

• special dampness (humidity about 100%);

  chemical active or organic medium acting on the insulation;

  simultaneous presence of 2 or more conditions for rooms of increased danger.

Premises without increased danger.

They do not contain conditions that create an increased or special danger.

Protective measures in electrical installations

Protection against the possibility of accidental contact with live parts.

Electrical networks and installations must be designed so that their current-carrying parts are inaccessible to accidental contact.

The inaccessibility of current-carrying parts is achieved by their reliable isolation, the use of protective fences (casings, covers, grids, etc.), the location of current-carrying parts at an inaccessible height.

In installations with voltages up to 1000 V, the use of insulated wires provides sufficient protection. In the case when it is impossible to achieve reliable isolation or fencing of live parts, interlocks (electrical and mechanical) are used to automatically turn off dangerous voltage when a person enters the danger zone. The design of the fences depends on the voltage of the installation. Guards must be designed so that they can be removed and opened with keys or a tool. Mesh fencing of current-carrying parts in residential, public and other domestic premises is not allowed. Fences should be solid here.

PUE provides different kinds testing and insulation control

1. Acceptance testing of insulation. All electrical machines and devices with voltage up to 1000 V are tested with a voltage of 1000 V for one minute.

   Periodic control of insulation. It is carried out by measuring the insulation resistance with a megohmmeter. The measurement is carried out on a switched off installation, the frequency of measurements is at least 1 time per year. The insulation resistance of the network up to 1000 V must be at least 0.5 MΩ.

Permanent insulation monitoring (PKI). PKI is carried out in networks with an isolated neutral. In practice, devices for constant control of types are used: on direct operational current and valve ones. The isolation control valve circuit is shown in fig. 12.1.

Rice. 12.1. Gate circuit

The device measures the insulation resistance of the entire network:

The disadvantages of the scheme:

if the device malfunctions, it shows ¥, i.e. good insulation;

the accuracy of the measurement depends on fluctuations in the mains voltage and on the degree of asymmetry of the insulation resistances.

Advantages: simplicity, no operational DC required.

The insulation control circuit on three voltmeters is shown in fig. 12.2.

Fig.12.2. Diagram of three voltmeters

The insulation control circuit on three voltmeters allows you to judge not only the deterioration of insulation, but also ground faults (deaf).

There are for such circuits and schemes for the zero sequence voltage or for the zero sequence current.

Application of low voltages. PTE and PTB establish voltage limits for manual current collectors for rooms of various categories.

For especially dangerous rooms:

portable lamps - voltage 12 V;

miner's lamps - voltage 2.5 V.

For hazardous areas:

hand tool - voltage 42 V;

lamps - voltage 42 V.

If it is impossible to use a voltage of 42 V, the PTB allows the use of a power tool for U = 220 V in the presence of a device protective shutdown or reliable grounding of the body of the power tool with the obligatory use of protective equipment (gloves, mats).

Transformers are used as low voltage sources. To reduce danger when crossing higher voltage in the network of the lower secondary winding of the transformer is grounded. The use of autotransformers as low voltage sources for powering portable power tools is prohibited.

double insulation. With double insulation, in addition to the main working insulation of current-carrying parts, another layer of insulation is used, which covers metal non-current-carrying parts that may be energized. It is possible to manufacture electrical equipment cases from insulating material (plastic, nylon). Widespread use of double insulation is limited due to the lack of plastics and coatings resistant to mechanical damage. Therefore, the scope of double insulation is limited. It is used in electrical equipment of low power (tools, portable current collectors, household appliances).

Potential equalization. This method is used when working on power lines, substations. At high-voltage substations, potential equalization is carried out by arranging grounding conductors along the contour around the grounded equipment at a small distance from each other, and horizontal strips are laid in the ground inside the circuit (Fig. 12.3).

Rice. 12.3. Earthing switch with potential equalization

The distance from the boundaries of the ground electrode to the fence of the electrical installation on the inside must be at least 3 m. As a result, the potential difference between the points inside the circuit is reduced and the touch voltage coefficient a is much less than unity. The step stress factor is also less than the maximum possible value.

Protection against the danger of voltage transition from high to low side. The appearance of a voltage in the network that is much higher than the nominal one can lead both to failure of current collectors, the insulation of which is not designed for this voltage, and to personal injury by current, since this usually causes a short circuit to the case and dangerous touch and step voltages appear.

Protection of networks with voltage up to 1000 V with an isolated neutral from a possible transition to this network of higher voltage is carried out by installing a breakdown fuse (Fig. 12.4).

Rice. 12.4. Scheme for switching on a breakdown fuse

Consider two cases at U 1l = 6000 V, U 2f = 220 V.

Closure on the high side. Punch-through fuse P is missing. When closed, the voltage between the neutral point and earth will be

.

The voltage of the phase wires of the 380 V network will be U 2F \u003d 3460 + 220 \u003d 3680 V.

The consequence of this case may be an insulation breakdown and the appearance of a voltage of 3680 V on the case.

U 2F \u003d 125 + 220 \u003d 345 V.

In this case, there will be no breakdown of the insulation. In networks with grounded neutral fuses are not installed. Safety in them is ensured by the correct choice of grounding resistance R З.

Protection against loss of attention, orientation and wrong actions th. This protection is carried out through the use of interlocks, alarms, special equipment coloring, markings, safety signs.

Dry rooms are rooms in which the relative humidity of the air does not exceed 60%.
Wet rooms are rooms in which vapors or condensing moisture are emitted only briefly in small quantities, and the relative humidity of the air is more than 60%, but does not exceed 75%.
Raw rooms are rooms where the relative humidity of the air exceeds 75% for a long time.
especially raw rooms are rooms in which the relative humidity of the air is close to 100% (the ceiling, walls, floor and objects in the room are covered with moisture).
hot rooms are rooms in which, under the influence of various thermal radiations, the temperature constantly or periodically (more than 1 day) exceeds +35 ° C (for example, rooms with dryers, drying and kilns, boiler rooms, etc.).
dusty rooms are rooms in which, according to production conditions, technological dust is released in such an amount that it can settle on wires, penetrate inside machines, apparatus, etc.
Dusty rooms are divided into rooms with conductive dust and rooms with non-conductive dust.
Premises withchemically active or organic environmentare rooms in which aggressive vapors, gases, liquids are constantly or for a long time, deposits or mold are formed that destroy the insulation and current-carrying parts of electrical equipment.
According to the risk of explosion or fire, the premises are explosive (six classes - B-l, B-la, c, g, B-II and B- II a) and flammable (four classes - P- I, P-II, P-III a, P-III ).
According to electrical safety conditions, electrical installations are divided into installations up to 1000 V and installations above 1000 V, active and inactive.

With regard to the danger of electric shock to people, there are:
1. Premises without increased danger, in which there are no conditions that create an increased or special danger.
2. Premises with increased danger, characterized by the presence in them of one of the following conditions that create an increased danger:
a) dampness or conductive dust (relative humidity exceeds 75%);
b) conductive floors (metal, earthen, reinforced concrete, brick, etc.);
c) high temperature (more than 35 °C);
d) the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological apparatus, mechanisms, etc., on the one hand, and to the metal cases of electrical equipment, on the other.
3. Particularly dangerous premises, characterized by the presence of one of the following conditions that create a particular hazard:
a) special dampness;
b) chemically active or organic environment;
c) simultaneously two or more conditions of increased danger.
4. Territories for placement of outdoor electrical installations. With regard to the danger of electric shock to people, these territories are equated to especially dangerous premises.

§ 4. Classification of premises according to the danger of electric shock.

The risk of electric shock depends on the environment and setting. Dampness, heat, caustic vapors and gases, conductive dust have a destructive effect on the insulation of electrical installations, significantly reducing its resistance. There is a danger of voltage transfer to non-current-carrying parts of electrical equipment (housings, frames, casings) with which the worker is in contact. Under such conditions, the electrical resistance of the human body also decreases, further increasing the risk of electric shock.

The danger is aggravated by the presence of conductive floors and metal grounded objects close to the equipment: if you simultaneously touch these objects and electrical equipment cases that accidentally become energized, a large current will pass through the human body. This necessitates the division of premises according to the degree of danger of electric shock.

The current rules for the installation of electrical installations (PUE) all rooms are subdivided for the next three classes.:

I. Premises without increased danger: dry, with normal temperature air, with non-conductive floors.

II. Premises with increased danger: damp with relative humidity air (long-term) more than 75%; hot with air temperature exceeding +30°C for a long time; with floors made of conductive materials; with a large amount of emitted conductive technological dust deposited on the wires and penetrating inside electrical installations; with the placement of electrical installations with metal cases connected to the ground, metal structures of buildings and technological equipment, allowing simultaneous contact with them.

III. Particularly dangerous premises: especially damp with relative air humidity close to 100%, chemically active environment, simultaneous presence of two or more conditions typical for premises with increased danger.

One of the measures to ensure electrical safety in rooms of II and III classes is the use of low voltage current.

As examples of the division of premises according to the degree of danger, the following can be cited: class I includes office premises and laboratories with precision instruments, assembly shops of instrument factories, watch factories, etc.; to class II - warehouse unheated premises, stairwells with conductive floors, etc.; to class III - all workshops of machine-building plants: galvanic, storage batteries, etc. They also include areas of work on the ground in the open and under a canopy.