Grounding is a protective measure against electric shock. Methods of personal protection against electric shock. Precautions to Protect Against Electric Shock

3 Technical measures and means of protection against electric shock

Some terms and definitions:

live part: The conductive part of the electrical installation, which is under operating voltage during its operation, including the neutral working conductor.

exposed conductive part: A conductive part of an electrical installation that is accessible to touch, not normally energized, but which may become energized if the main insulation is damaged (for example: the metal housing of an electric motor).

With external conductive part: Conductive part that is not part of the electrical installation (for example: metal heating pipes).

direct touch: Electrical contact of people or animals with live parts.

indirect touch: Electrical contact of people or animals with exposed conductive parts that become live due to insulation failure.

ultra-low (small) voltage: Voltage not exceeding 50 V AC and 120 V DC.

automatic power off: Automatic opening of the circuit of one or more phase conductors (and, if required, the neutral working conductor), performed for safety purposes.

potential equalization: Electrical connection of conductive parts to achieve equality of their potentials.

3.1 Precautions against electric shock

Electric shock can occur from direct human contact with live parts of an electrical installation, as well as when touching exposed live parts (metal parts of an electrical installation) in cases of insulation damage. To protect against electric shock from direct contact with live parts, the following protective measures are applied individually or in combination:

basic insulation of live parts;

fencing and shells;

installation of barriers;

placing live parts out of reach;

use of ultra-low (small) voltage – not exceeding 50 V AC and 120 V DC.

To protect against electric shock in the event of insulation damage, the following protective measures for indirect contact are applied:

protective grounding;

protective automatic power off (including using protective grounding, residual current devices);

equalization of potentials;

potential equalization;

double or reinforced insulation;

ultra-low (low) voltage;

protective electrical separation of networks;

insulating (non-conductive) rooms, zones, areas.

Protection against direct contact is not required if the electrical equipment is located in a potential equalization zone and the highest operating voltage does not exceed 25 V AC or 60 V DC in non-hazardous locations and 6 V AC or 15 V DC in all cases. Protection against indirect contact should be carried out in all cases where the voltage in electrical installations exceeds 50 V AC and 120 V DC. In hazardous areas, particularly hazardous and outdoor installations, indirect contact protection may be required at lower voltages.

The conditions for applying protective measures (taking into account GOST R 50571.3-94. Safety requirements. Protection against electric shock) can be presented in the form of diagram 3.1

Scheme 3.1 – Conditions for using protective equipment

When a current exceeding 30 mA passes through a person’s body, a threat to his health arises. Adverse effects affect muscle tissue, respiratory organs, and the functional state of the heart. The current must be turned off quickly enough to prevent the situation from becoming life-threatening. It's even better to use special means and measures to prevent the occurrence of relevant situations.

Definitions and standards

Measures for protection against electric shock are set out in detail in the state standard of the Russian Federation GOST R IEC 61140-2000, which came into force on January 1. 2002. Its main provisions are identical to international standards. This document is basic. On its basis, it is permissible to develop federal, industry and other standards. The terminology used corresponds to the data of international specialized (electrical) dictionaries.

The scope of this document applies to electrical equipment that uses voltages up to 1,000 V AC, or up to 1,500 V DC. The rules apply not only to individual installations, but also to systems and their mutual connections.

For additional clarification on individual parameters of security equipment, specialized standards are used. So, to learn more about the protective properties of the insulating shells of conductors, you can study the state standard of the Russian Federation 14254 - 96.

Explanations of some of the main definitions:

1. By “direct” we mean the touch of a person to a conductor that is energized. But dangerous situations also occur in the event of an insulation breakdown. If a piece of equipment is not normally a conductive part, another term is used - “indirect contact”.
2. Insulation is not only the polymer sheath of the wire. It can be liquid (oil in a transformer), gaseous (air gap).
3. The reinforced insulation version consists of at least two parts. Each of them cannot be tested separately as a main or additional protective layer.
4. In addition to insulation, safety measures also include:
   

• non-conducting environments - floors, walls;
• devices and fences preventing unauthorized access;
• shells that prevent contact with live elements;
• means ensuring the same potential between the conductor and the ground;
• systems that disconnect one or more conductors in the event of an emergency;
• use of low voltage.

Personal and automatic means of protection

In any case, when building a high-quality security system, the basic rule must be observed: “dangerous parts (conducting current) are made inaccessible, accessible parts should not pose a danger to humans.”

Security measures

The above rule is considered under normal conditions when a malfunction occurs. For the first case, basic protection will suffice. It is made up of measures (one or more) that can prevent human contact with a conductive part. Below are several options:

• Solid insulation to prevent contact with the conductor.
• Air insulation. In this case, it alone is not enough; a barrier is needed to prevent access by unauthorized persons. This type of fencing is made with high strength. If necessary, it is equipped with locking devices that can be opened using keys, codes or other special devices.
• Placing conductive parts too far apart to physically allow them to be touched at the same time.
• Use of lighting devices and electric tools operating at low supply voltage (from 12 to 36 V). To create an appropriate system, step-down transformers are used. An additional safety feature is to ground their secondary windings.
• Limiting the current level to no more than 2 mA, which flows at a resistance of 2 kOhm.

General view of a step-down transformer

The numbers in the last paragraph are indicated only for a specific situation. They will be different for direct current. Appropriate limiting standards have been established for direct current, pain threshold, and static charge magnitude. The shape of the electrical signal and its frequency should also be taken into account.

For the second case, when a malfunction occurs, other measures are applied, in addition to the points listed above, or independently:

1. Insulation that can withstand the same voltage levels as the base layer.

1. Potential equalization system. It is usually made up of several parts:
   

• grounding conductor;
• metal structures, pipeline;
• connecting parts with conductors in local volumes where special conditions exist.

1. An automatic device that turns off the power when dangerous operating conditions occur.

Protective measures

Now let's talk more about the main and auxiliary safety features. Since their exact composition depends on specific conditions, reference should be made to the basic protective measures and those required when malfunctions occur.

Grounding and installations with isolated neutral

Measures to protect against electric shock and their features

Similarly, the state standard defines the parameters of the following safety equipment:

• separation by a non-conducting medium;
• use of SELV and PELV systems;
• limiting the touch current level in steady state;
• limitation of electric charge.

Classification

Electrical equipment is divided into special protection classes. This simplifies the creation of effective protection measures in difficult situations, compliance with the requirements of government regulatory authorities and other practical actions . Features of protection classes:

• Class "0". Such equipment uses insulation as the primary protective measure. Additional safety measures are not provided in the event of malfunctions.
• Class "1". This group includes equipment equipped with a potential equalization system. It operates when a fault occurs and prevents electric shock. In these installations, the conductive elements are connected to a special clamp. During the installation process it is connected to a potential equalization system. To avoid errors, such places are marked with a special sign, the letters “PE”, and a color combination (yellow and green).
• Class "2". This equipment uses basic and additional insulation. In protective shells, it is not allowed to use fasteners that do not conduct current, which can be removed for maintenance or replaced with metal analogues.
• Class “3” equipment uses ultra-low voltages that do not exceed 50 V (AC) or 120 V (DC). Its operation is possible in any mode, and situations dangerous to humans are excluded. That is why connecting such devices to neutral conductors for protection is not necessary.

Additional Requirements

Safety features should be considered in conjunction with the conditions of their use. For example, some devices (automatic machines, fuses) must be returned to their original position after tripping, or replaced. To keep electrical equipment in working order long time inspections are carried out regularly, maintenance. Ensure that sufficient protective measures are in place when performing such operations.

If routine maintenance is expected to be carried out manually, dangerous live parts are located in inaccessible places. If this requirement cannot be met, special devices are used. They provide reliable isolation from the electrical power source.

Enclosures and guards should only be removed for work by personnel with the appropriate skills. The qualifications of specialists are documented (an admission group is established). Their knowledge is checked regularly, for which special commissions are created at enterprises.

Studying electrical safety rules

Video about helping the victim

This video talks about the features of providing first aid to an electric shock victim and about resuscitation measures.

Access to protective elements and devices cannot be restricted. They are placed in clearly visible places. A separate standard has been established for situations where the main means of protection is to disconnect electrical installations from the current source. This requires removing the casing and dismantling the fence. In these cases, capacitor devices must discharge automatically to a safe level in no more than 5 seconds. If this condition is not met, then a sign with an inscription warning about the real discharge time is required.

According to Russian statistics, the number of fatal injuries due to electric current is approximately 2.7% of the total number of all fatalities. The most common cause of injury is electrical installations operating under voltages of up to 1000 volts. This is due to their widespread use and contacts with them large quantity people who do not have special training in electrical engineering.

The dangerous state of electrical equipment cannot be determined without special instruments. Therefore, when working with it, means of protection against electric shock become of great importance.

The effect of current on the human body

In order to use protective equipment correctly, you need to know what effect electric current has on a person. First of all, the human body is exposed to thermal, biological and chemical influences. Quite often it is accompanied by secondary injuries. All this leads not only to local tissue damage, but also to a general disruption of body functions.

As a result of biological effects, vital organs such as the cardiovascular and central nervous systems are damaged. Their normal functioning is based on electrical processes, therefore the external action of electric current leads to destruction and physiological incompatibility with it.

High frequency currents can cause thermal effects. Sources can be metal objects and resistors heated by current, exposed live parts, an electric arc and other factors. Under the influence of current, the human body is exposed to chemical effects. It consists of polar and non-polar molecules, anions and cations. All of them perform chaotic continuous thermal movements, ensuring the vital activity of all organs and systems. Chaotic movement is replaced by strictly oriented movement of ions and molecules, which leads to disruption of the normal functioning of the body.

How to avoid electric shock

Measures to ensure electrical safety are defined in the Electrical Installation Rules (PUE). First of all, live parts are blocked and fenced, and free access to them is limited. These means are very effective in case of accidental entry into a dangerous area or when a person comes into contact with live parts of equipment.

In the premises where they are located, dangerous zones are identified by installing fences with a height of at least 1.7 m. The fencing of open areas must have a height of 2 meters or more. The blocking system provides for certain actions to disconnect or relieve voltage from live parts. As a result, a person simply will not be able to get into the danger zone. Typically, electrical installations are blocked during opening doors, removing fences and other work during which there is free access to dangerous places.

One of the effective measures is to use low voltage, up to 42 watts. It is used in portable and local lighting, hand tools and other places. In addition, local stationary lighting is provided in rooms with an increased and high degree of danger. Closed metal containers are illuminated by lamps with a voltage not exceeding 12 volts.

Quite often, the method of electrically dividing networks into separate sections is used. For this purpose, isolation transformers are used to separate networks with neutral and networks supplying power to the receiver. The power supply and receiver networks are interconnected using magnetic fields. In this case, the receiver itself and the section of its network are not connected to the ground. The transformer provides power to only one receiver, with a current not exceeding 15 amperes.

The housings of devices and installations are equipped with protective grounding. In this case, their non-current-carrying metal parts are connected to the ground using special structures. These systems eliminate the danger of electric shock if a person carelessly touches live parts that are energized.

If there is a danger of electric shock, a protective shutdown of the network is applied for a period of time not exceeding 0.2 seconds. For these purposes, special protective shutdown devices are used. They are equipped with a sensitive element that responds to changing parameters of the controlled voltage. As a result, the required section of the circuit is disconnected. The RCD is triggered when a person directly touches live parts.

Special protective equipment

In addition to general measures, there are specific means that protect against electric shock. According to their purpose, all means can be isolating, fencing and auxiliary. The main function of insulating means is to isolate people from live parts of energized installations. In addition, insulation from the ground is ensured while simultaneously contacting live and grounding parts.

The main insulating protective equipment used in installations up to 1000 volts consists of dielectric gloves, pliers for measuring current and replacing fuses, plumbing tools equipped with insulating handles, and voltage indicators.

For electrical installations with voltages greater than 1000 volts, measuring and insulating rods, voltage indicators and current clamps are used as the main protective equipment. In addition, they apply various types removable insulating ladders and towers. Additional insulating means are represented by boots, galoshes, and special stands with porcelain insulators.

The main purpose of fencing protective devices is the temporary fencing of live parts that are energized. The most common practice is to use barriers, shields, and fences in the form of cages. The use of temporary ones completely eliminates the occurrence of voltage on disconnected equipment.

The purpose of the auxiliary equipment is to protect working personnel from accidental falls from a height, damage to the eyes and other vital organs. For this purpose, safety ropes, claws, safety belts, mittens, safety glasses, special suits, etc. are used.

When drawing up a project, safety issues must be coordinated with all supervisory authorities, in strict accordance with the PUE. However, during operation, compliance with electrical safety measures depends on specific people - the organizers and performers of the work. Therefore, means of protection against electric shock are of great importance in ensuring safe conditions labor.

According to requirements regulatory documents, the safety of electrical installations is ensured by the following basic measures:

• 1) inaccessibility of live parts;
• 2) proper, and in some cases increased (double) insulation;
• 3) grounding or grounding of electrical equipment housings and electrical installation elements that may be energized;
• 4) reliable and fast automatic protective shutdown;
• 5) the use of reduced voltages (42 V and below) to power portable pantographs;
• 6) protective separation of circuits;
• 7) blocking, warning alarms, inscriptions and posters;
• 8) use of protective equipment and devices;
• 9) carrying out scheduled maintenance and preventive testing of electrical equipment, devices and networks in operation;
• 10) carrying out a series organizational events(special training, certification and recertification of electrical personnel, briefings, etc.).

To ensure electrical safety at meat and dairy industry enterprises, the following technical methods and means of protection are used: protective grounding, grounding, the use of low voltages, control of winding insulation, means personal protection and safety devices, protective shutdown devices.

Protective grounding is the intentional electrical connection to earth or its equivalent of metallic non-current-carrying parts that may be energized. It protects against electric shock when touching metal casings of equipment, metal structures of electrical installations, which become energized due to failure of electrical insulation.

The essence of the protection is that during a short circuit, the current flows through both parallel branches and is distributed between them in inverse proportion to their resistances. Since the resistance of the man-to-ground circuit is many times greater than the resistance of the body-to-ground circuit, the strength of the current passing through the person is reduced.

Depending on the location of the grounding electrode relative to the equipment being grounded, remote and loop grounding devices are distinguished.

Remote grounding switches are located at a certain distance from the equipment, while the grounded housings of electrical installations are on the ground with zero potential, and a person touching the housing is under the full voltage of the grounding switch.

Loop grounding switches are placed along the contour around the equipment in close proximity, so the equipment is located in the current flow zone. In this case, when there is a short circuit to the housing, the ground potential on the territory of an electrical installation (for example, a substation) acquires values ​​close to the potential of the ground electrode and grounded electrical equipment, and the touch voltage decreases.

Zeroing- this is an intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized. With such an electrical connection, if it is reliably made, any short circuit to the housing turns into a single-phase short circuit (i.e. a short circuit between the phases and the neutral wire). In this case, a current of such strength arises that the protection (fuse or circuit breaker) is activated and the damaged installation is automatically disconnected from the supply network.

Low voltage- voltage not exceeding 42 V, used to reduce the risk of electric shock. Low AC voltages are obtained using step-down transformers. It is used when working with portable power tools, when using portable lamps during installation, dismantling and repair of equipment, as well as in remote control circuits.

Isolation of the workplace- this is a set of measures to prevent the occurrence of a human-earth current circuit and increase the value of the transition resistance in this circuit. This protective measure is used in cases of increased risk of electric shock and usually in combination with an isolating transformer.

The following types of insulation are distinguished:

• · working - electrical insulation of live parts of an electrical installation, ensuring its normal operation and protection from electric shock;
• · additional - electrical insulation provided in addition to the working insulation to protect against electric shock in the event of damage to the working insulation;
• · double - electrical insulation, consisting of working and additional insulation. Double insulation consists of one electrical receiver having two stages of insulation independent of one another (for example, covering electrical equipment with a layer of insulating material - paint, film, varnish, enamel, etc.). The use of double insulation is most rational when, in addition to the working electrical insulation of live parts, the body of the electrical receiver is made of insulating material (plastic, fiberglass).

Safety shutdown- this is a fast-acting protection that ensures automatic shutdown of an electrical installation when there is a danger of electric shock.

It should ensure automatic shutdown of electrical installations in the event of single-phase (single-pole) contact with parts energized that are not permissible for humans, and (or) when a leakage current (short circuit) occurs in the electrical installation exceeding specified values.

Protective shutdown is recommended as a primary or additional protective measure if safety cannot be ensured by grounding or grounding, or if grounding or grounding is difficult to implement or is not practical for economic reasons. Devices (devices) for protective shutdown with regard to reliability of operation must meet special technical requirements.

Personal protective equipment is divided into insulating, auxiliary and fencing.

Insulating protective equipment provides electrical isolation of a person from live parts and the ground. They are divided into basic (dielectric gloves, tools with insulated handles) and additional (dielectric galoshes, mats, stands)

Auxiliary items include goggles, gas masks, masks designed to protect against light, heat and mechanical influences.

Boundaries include portable shields, cages, insulating pads, portable grounds and posters. They are intended mainly for temporary fencing of live parts that may be touched by workers.

To ensure a good level of safety when working with electrical installations, a set of special organizational and technical measures is used. It includes individual and collective means protection, personnel training and knowledge testing system, grounding, automatic equipment shutdown, and other means.

Energy must be safe

Regulations and standards

The thematic rules are set out in detail in the relevant state standards. They are created taking into account international standards, based on practical experience, scientific knowledge, laboratory research, and testing. General provisions, technical and organizational means are given in GOST IEC 61140-2012. This document came into force on July 1, 2014. It has been ratified by the authorized bodies of the CIS countries. Practitioners use the Electrical Installation Rules in different versions (PUE). Currently, the 7th edition is relevant for the Russian Federation.

The standards indicate that the scope of the standards for protecting people from electric shock applies to all electrical equipment. A division has been made into two main groups:

• low voltage – up to 1000 V AC (1500 V DC);
• high voltage - above 1000/1500 V, respectively.

Features of some terms used in this article:

• Basic protection against electric shock is designed for normal conditions. In fact, the possibility of damage, high humidity, and other significant additional factors are taken into account.
• At high voltages, not only the conductor, but also the insulation surface is considered a dangerous part for humans.
• A protective barrier is created to prevent personnel from accidentally accessing certain parts of the equipment. The fence does not allow entry to them from any direction.
• The main insulating layer provides human protection under normal conditions. Additional – performs the same functions if damaged. Double insulation refers to the presence of two layers at the same time.
• Step voltage is called voltage between points located at a distance of 1 meter from each other (clause 3.33. GOST IEC 61140-2012).
• The following technical current/charge limits apply when calculating the parameters of certain protective equipment:
  

1. The perceptible threshold is 0.5 mA alternating (2 mA direct) current.
2. The pain threshold is 3.5 and 10 mA, respectively.
3. In the presence of a charge, the perceptible threshold is 0.5 μC, and the pain threshold is 100 times higher.

Technical passive protection

This category includes reliable conductor insulation that prevents human contact with live parts. The layer parameters are calculated taking into account possible mechanical and other external influences. It must prevent the penetration of water and oxygen to prevent the occurrence and development of corrosive processes. Its resistance is created by at least 0.5 MOhm relative to ground. If double insulation is used, then the minimum allowable resistance is 10 times greater.

To protect a person from electric shock, grounding is used. To do this, connect metal cases and equipment frames with a conductor to a grounding element (circuit). When shorting, you can feel the touch voltage, but the current will not be dangerous. Such a system must be used when installing installations operating with three-phase 380 V networks.

Grounding diagram in a private house

The grounding device can be remote or contour. The second scheme is more effective. It assumes a close distance from the equipment to grounding points. If possible, the conductor is connected to water supply pipelines and metal parts of foundations.

Connection to gas mains is not allowed. If necessary, metal elements specially made for this purpose are immersed in the ground. The resistance of the connecting conductor should not exceed 4 ohms for low voltage equipment. But for private consumers, a maximum of 30 Ohms is acceptable.

This category of passive protective equipment also includes reducing the supply voltage of electricity consumers to a level that is safe for humans (42 V). The above figures are only approximate. For an accurate calculation, it is necessary to take into account the specific conditions and standards established in the PUE.

Active technical protection

In three-phase four-wire AC networks, a “zeroing” circuit is used. To equalize potentials when emergency situations, one of the wires is grounded and connected to the equipment body. If a short circuit (SC) occurs, the corresponding section of the network will be disconnected. To do this, fuses or circuit breakers are included in the circuit.

Such personnel protection means will work accurately if the calculated current during a short circuit exceeds the rating of the fuse-link by at least three times.

In the same way, taking into account conductivity, the model of the circuit breaker is selected. In this case, it is permissible to use a lower multiple of current values ​​in relation to the short circuit mode, more than 1.4 times when operating with voltages up to 1000 V. Modern models of such devices ensure that the current supply is turned off in approximately 0.01 s.

Circuit breaker model

To increase the reliability of such a circuit, select the minimum possible resistance of the protective circuit circuit. The neutral conductor is connected to the ground in several places, so even if there is a break, the necessary function will be performed.

Units are disconnected from single-phase networks using specialized protective devices. They are triggered if the insulation resistance decreases or a person touches live parts of the equipment. They are used separately, and also as an addition to grounding (grounding).

Machine selection parameters

Preventive Actions

IN the following list The following are measures that will ensure restriction of human access to a certain area and inform about potential dangers:

• Barriers. They are intended for qualified workers, but are not able to prevent access by people who accidentally find themselves in the danger zone. These designs do not allow contact with live parts of the equipment.
• Fences are created with sufficiently high mechanical strength. They are equipped with locking mechanisms or connections that can only be disconnected with the use of tools.
• Light, color and sound alarms will prevent personnel or unauthorized persons from performing incorrect actions. In some situations, the desired result is achieved by installing special blocking devices.

Fencing of electrical installations to restrict access of unauthorized persons

Individual means

When carrying out work, specialists use:

• The rods and pliers used to make measurements are replaced with fuse links. Special screwdrivers, pliers, wrenches. Phase and voltage indicators. All listed products are equipped with insulating handles that prevent electric shock to humans.
• Rugs, galoshes, gloves made of dielectric materials. Masks, respirators, helmets, other protective equipment.

Personal protective equipment against electric shock

• Mobile grounding devices.
• Signs warning of work on electrical equipment. Signs prohibiting entry into the danger zone.

If necessary, use stepladders, towers, safety belts and ropes, gas masks and respirators, safety glasses and special clothing.

Organizational events

The following measures will help prevent hazardous situations from occurring:

• Proper operation of the HR department of the enterprise. Selection for work in the relevant departments of employees who do not have health restrictions and have reached the age of 18 years. Good physical and mental condition must be confirmed by official certificates of professional medical examinations.
• Full training of personnel in the rules of servicing electrical installations, taking into account current safety standards. The acquired knowledge is tested. Before performing work, instructions are given. Job Descriptions are developed taking into account the current GOST standards and are officially approved by order in writing.
• A person is appointed responsible for electrical equipment and compliance with safety regulations.
• IN established by standards terms, insulation and other parameters are monitored electrical networks. To do this, use the appropriate regulations, which are collected in a single document “Rules for the construction of electrical installations”. The seventh edition of the collection is in effect in Russia. Latest changes were approved by the Ministry of Energy of the Russian Federation on July 8, 2002 for industrial enterprises with a validity period of January 1, 2003. The frequency of inspections is established depending on the characteristics of the equipment and its operating conditions.

Additional measures

The above-mentioned “Electrical Installation Rules” are not standards. They do not include provisions related to the protection of equipment during fires and thunderstorms. That is why it is necessary to develop effective protection taking into account the characteristics of specific tasks.

Special measures are used in the presence of increased electric field strength in the room.

We must remember that exceeding the norms can cause significant changes in the state of the cardiovascular and nervous systems human body.

Video about SZ

You can learn about existing means of protection against electric shock from the video below.

Static charges can have a negative impact on health. They are eliminated through the correct use of materials in the manufacture of housings and other parts of units and machines. Some modern products do not electrify even in the presence of conditions conducive to this process. Remove excess charge by grounding. In some cases, the desired result is obtained by increasing humidity, adding conductive additives, or changing other parameters technological processes in the process of processing dielectric raw materials.