Personal protective equipment during the operation of electrical installations. Electrical protective equipment general provisions. Protective equipment against electrical fields

In the case of currently used electrical installations based on three wires, a protective contact, and through it, the device housing is connected to an earthed protective conductor. This solution allows the use of safety switches in a protected circuit.

Solutions described as protection against electric shock also include the use of double insulated devices. In this case, in addition to the basic insulation, the device uses additional insulation, usually in the form of a device made of insulating material.

In the event of damage to the main insulation of the device, this solution eliminates the possibility of hazardous voltages on the case. Protected devices can be easily identified by power plugs without protective contacts and a special symbol on the device body: two squares located in the other.

Another way to protect against electric shock is by using electrical separation. The devices are then powered by special, usually portable, isolation transformers with increased insulation between the windings, with a single transformer capable of operating only one device. In this case, if a short circuit occurs in the enclosure of the protected device - if it is touched by a person - only a small shock current will flow through the enclosure.

This is due to the fact that the electrical circuit in this case is closed only by the power of the wires and their resistance. For this purpose, the aforementioned RCDs are used with a rated RCD current not exceeding 30 mA, and by creating additional connections, a protective equipotential connection between the conductive components of the premises.

The advantage of introducing additional compensating couplings is that when voltage is applied to one of the devices, the user will not be paralyzed, because the metal connection of all conductive elements will give them the same voltage, that is, the potential difference required for the body of a person passed electricity.

Circuit breaker - how does it work?

In simplified terms, the job of an RCD is to compare the amount of current flowing through a phase conductor into a protected supply circuit with the amount of neutral current flowing. When a difference is established between these values, the circuit breaker automatically cuts off power to the protected circuit.

The design and principle of operation of the circuit breaker. A difference in the amount of current flowing indicates that either the insulation was damaged in the circuit, or a short circuit between phase and earth, or a short circuit of the phase conductor through conductive elements to earth or other grounded elements. In some cases, some of the current flowing through the phase conductor around the perimeter may be "released" through the resistance of the human body, which accidentally touches the body of the damaged electrical device powered by the protected circuit.

The value of the difference between the current that triggers the differential current switch is called the differential current, and the value at which the circuit breaker operates and trips the circuit depends on the task at hand. If an earth leakage circuit breaker is to be used as an anti-shock element, the differential operating current should not exceed 30mA, that is, the maximum value of the human safety circuit.

Circuit breakers with a residual current of 500 mA are also used in electrical installations for fire protection applications in the event of a short circuit in circuits. Over time, due to aging of electrical insulation or damage to it in the system, a current flows, the value of which is still too low to provide overcurrent protection, but it is high enough to lead to local overheating of the wires and therefore cause a fire.

Due to the possibility of breaking short-circuit currents, the circuit breaker structures can be divided into two groups. Non-overcurrent circuit breakers - Their working contacts are not designed to trip high currents and usually require a fuse or overcurrent protection. Circuit breakers with overcurrent switches are equipped, like circuit breakers, with overcurrent triggers with triggers of type B or C. They are often used in solutions where the circuit supplies only one device, for example, to protect the output of a washing machine. This solution also saves space in electrical switchgear. ... The increase in the use of electronic devices equipped with high capacitance capacitors leads to the need for conventional circuit breakers, identifying the instantaneous charging current of the capacitor in the device as a crosstalk current.

Therefore, care should be taken to select a circuit breaker with the required characteristics in accordance with your needs. Due to the shape of the differential current to which RCDs react, their structures can be divided into 3 types. Each of the differential switches is equipped with a system to check its technical efficiency. Due to the important role of resistance to electric shock in an electrical system, its operation must be monitored regularly.

To check its excluding ability, a control circuit simulation circuit is provided, consisting of a control button and a corresponding resistor built into its case. By pressing the control button, we generate a differential current with values ​​slightly higher than the excitation current of the circuit breaker. Immediate activation of the circuit breaker confirms its mechanical properties.

The rules also require the use of compensation links - basic and additional. The main element of the main equalization connection is the grounding rod with terminals for connecting protective conductors. It is located at or near the lowest level of the switchgear. All metal pipes and metal fittings for cold water, hot water, sewerage, central heating, gas, air conditioning, metal coatings and cable sheaths, as well as metal structural elements of the building are connected to this rail.

In all areas where there is an increased risk of injury, additional compensating connections must also be made to connect all conductive elements. You will also need to attach the tub or tray to the compensation system if you are metal.

An important function of earthworm protection systems is the grounding of electrodes, preferably natural, and in the absence of them - artificial, galvanized or copper or copper in the form of tapes, pipes, sections, slabs and rods laid in the ground or in the foundation.

Horizontal strips of strips and wires must be laid at a depth of at least 0.6 m below the ground and vertically - from pipes or sections, so that the lowest part is at a depth of at least 2.5 m, and the highest is 0.5 m below the ground. The joints must be strong: welded, twisted, crimped or glued and protected from corrosion.

Circuit breakers are becoming a widespread element of protection against indirect contact. This is especially the case for shock protection solutions for electrical installations that are currently under construction or modernization. Such activity maintains records in technical and standard terms.

The standard specifies that in alternating current networks, additional protection by means of switches must be used for plug-in circuits with rated currents not exceeding 20 A, which are operated by ordinary users, and these vessels are used for general purposes. These switches should also be used on circuits rated up to 32A that are supplied by mobile receivers for outdoor use.

Therefore, it is possible to consciously transmit an electric current through a person. In the event that the circuit is protected by an overvoltage protection device, the current flowing through the human body when touching the active part will usually result in fatal damage, since the fuse will not handle currents of such magnitude that people can be fatal. The term "short-term" should be considered as contractual. Further attention will be paid to the shunt current times.

It is allowed to install earth leakage breakers without a protective conductor, provided that the rated breaking current of the circuit breaker does not exceed 20 mA, and the missing protective conductor limits the effectiveness of the additional protection, can be considered acceptable.

This content contains two dangerous entries that cannot be found in the current requirements. First, deliberately allow the flow of electricity through human body... The second entry is "considered acceptable." Immediate questions arise: who should recognize and what criteria and what definition is “acceptable”?

The regulation in § 2 provides for a softer requirement. "It is allowed to install shock-proof switches without a protective conductor, provided that the rated residual current does not exceed 30 mA." This is only a seemingly softer requirement, since higher currents are allowed that can flow through the human body, which do not trip the circuit breaker. This is because the switch also has another parameter, which is differential current without blocking.

At this current value, the upper limit of the self-discharge current must be considered. This value is considered to be 6 mA. Some authors accept 10mA or even 15mA. The fire time with such currents can be quite long. This, however, is limited to self-harm, because it usually comes off a captured electrode or is detached by others.

If there is no breakdown and the flow of this current is prolonged, involuntary muscle contraction, difficulty breathing, reversible heart failure and cardiac arrest can occur after more than 1 second. With a continuous current of 10 mA, effects can occur after more than 2 seconds.