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Prevention of electrocutions. Occupational Safety and Health

Occupational Safety and Health / electrical safety

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Electrocution of people in the conditions of an industrial enterprise are prevented due to:

1. technical solutions that exclude the possibility of including people in the current circuit between two phases or between one phase and the ground, in a way in which current-carrying parts that are normally energized are not accessible for accidental contact. This is ensured by reliable insulation, fencing, their location at an inaccessible height or underground, blocking and other methods;
2. removing voltage from current-carrying parts during work, in which the possibility of touching them is not ruled out;
3. protective grounding or automatic shutdown devices that provide isolation and voltage transfer to the metal parts of electrical devices in case of damage, limiting the voltage in magnitude or disconnecting faulty equipment and apparatus;
4. the use of safe voltage in electrical devices, depending on the conditions in which they are operated;
5. choosing the right work environment. It should be borne in mind that moisture, dampness, conductive dust, caustic vapors and gases (leading to the destruction of insulation), high air temperature, conductive floors (metal, earthen, reinforced concrete, etc.). the presence of a large number of grounded metal equipment increases the danger of electrical installations.

The following describes how to protect people from electric shock in the event of voltage on equipment that is not energized.

Protective earth. This is the name of the deliberate electrical connection of equipment to the ground using grounding conductors (Fig. 3). It is performed in order to reduce the voltage to a safe one. According to the Rules, the protective earth resistance should not exceed 4 ohms.

Thus, when touching the body of the equipment, which is energized, a person is connected in parallel to the current circuit. But in this case, due to the small resistance of the grounding conductors, a current of a safe value will pass through the person.

Rice. 3. Protective grounding scheme: a - in a network with an isolated neutral; b - in a network with a grounded neutral.

Grounding is subject to: cases of electrical machines, transformers, devices, lamps; drives of electrical devices; secondary windings of measuring transformers; frames of switchboards, control panels and cabinets; metal structures of switchgears, metal cable structures, metal cases of cable boxes; metal sheaths and armor of control and power cables, wires; steel pipes for electrical wiring and other metal structures associated with the installation of electrical equipment; lamp fittings, metal cases of mobile and portable power receivers, etc.

The norms and techniques for performing protective grounding are regulated by the "Rules for the technical operation of consumer electrical installations" and "Safety regulations for the operation of consumer electrical installations".

Protective grounding. Zeroing is a protective measure that is used only in networks with a grounded neutral voltage up to 380/220 V. It, like grounding, is designed to protect people if they touch equipment that has been “punched” onto the case. Constructive zeroing - joining near. pressing the protection of the object to the neutral wire of the network (Fig. 4).

The use instead of protective grounding in networks with deaf grounding of the neutral with a voltage of up to 1000 V neutral is caused by unreliable operation of grounding under these conditions. This is explained by the fact that when grounding, in the event of a breakdown to the case, the single-phase short circuit current between the equipment case and the grounded neutral is often insufficient in magnitude to melt the calibrated fuse links. And vice versa, when zeroing, the current that occurs during a voltage breakdown on the case is sufficient for the rapid melting of fuse-links or the operation of maximum protection. However, zeroing does not create protection in all cases.

Rice. 4. Scheme of protective zeroing

Safety shutdown. This is the name of the protection system based on the automatic shutdown of the pantograph in the event that a current appears on its metal parts that are not normally energized. Protective shutdown is carried out using circuit breakers or contactors equipped with a special protective shutdown relay from the network of a damaged current receiver. The advantage of a protective shutdown is its instantaneous (approximately 0,02 s) action. In addition, a protective shutdown can be triggered even at the very beginning of a fault. However, it sometimes does not work if the contact burns or the wire comes off, but its use is certainly advisable, especially when for some reason it is impossible to use protective grounding or grounding.

Protection against the transition of high voltage to the low voltage network. The transition of higher voltage to a lower voltage network is a dangerous phenomenon. It can occur mainly during the operation of power and instrument transformers, when the primary and secondary windings are connected.

This is also possible as a result of breakage and contact of high voltage wires with low voltage wires or installations.

Protection against these dangerous phenomena is grounding or zeroing of the secondary winding of transformers in case of violation of the insulation of the primary and secondary windings. This solution is effective for protecting against electric shock in transformers with a primary voltage of less than 1000 V and a secondary voltage of less than 100 V.

In addition to this measure, in networks with an isolated neutral, a breakdown fuse is installed on the way to the grounding device.

Portable temporary fences and posters. To prevent the possibility of accidental penetration and even more touching live parts under voltage, protective mesh and mixed fences are used (Table 2), as well as a system of warning posters.

Table 2. Permissible distances of fences from live parts

Distances from temporary fences to current-carrying parts under voltage above 1000 V are also established.

Temporary fences can be special solid or lattice wooden screens, shields, products made of micanite, rubber and other insulating materials in a dry state, well reinforced or firmly installed. The following warning posters are used for electrical installations (Fig. 5): cautionary, including "High voltage - dangerous for life!", "Under voltage. Dangerous for life!", "Stop! High voltage", "Don't get in, it will kill you!", "Stop! Dangerous for life"; prohibiting: "Do not turn on - people are working", "Do not open - people are working", "Do not turn on - work on the line"; permitting: "Work here", "Get in here"; reminiscent of: "Grounded".

Rice. 5. Warning posters.

Each poster has its own shape, corresponding image.

Their drawings, size and design, place and conditions of use are determined by the Rules.

Adaptations and personal protective equipment. Personal protective equipment and devices include instruments, apparatus, fixtures and devices designed to protect personnel servicing electrical installations from electric shock, exposure to an electric arc.

Isolating means of protection are divided into basic and auxiliary. The main ones include: operational and measuring rods, insulating and current clamps, voltage indicators, insulating devices and devices for repair work (insulating ladders, platforms, etc.). Auxiliary ones include: dielectric gloves, boots, rubber mats, insulating stands.

It follows from the foregoing that the main means of protection include those that can withstand the operating voltage of the installation for a long time, and the auxiliary ones are designed to strengthen the fixed assets. An example is the maintenance of high voltage installations, in which the main means of protection are insulating rods, pliers, voltage indicators, and auxiliary ones are dielectric boots, galoshes, gloves, insulating stands and rubber mats.

The administration of the enterprise is responsible for regular, in accordance with the established deadlines, testing and checking the serviceability of safety devices, dielectric galoshes and gloves, as well as timely replacement of filters, glasses and other parts with reduced protective properties.

 We recommend interesting articles Section Occupational Safety and Health:

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