Isolation of circuit breakers: insulation requirements for domestic and industrial appliances

The safe operation of all types of electrical equipment directly depends on the actual condition of the insulating materials that are embedded in the design of the live parts of each installation product. If the insulation of the circuit breakers is broken, there may be a power failure, fire, and even an accident.

We will tell you all about the types of insulation that ensure the full safety of using switching devices. In our proposed article, natural and synthetic, conventional and enhanced options are described in detail. Features of marking are given, advice to buyers is given.

Electrical insulation

Insulation materials protect people and animals from electric shocks. There is only one condition: you need to choose the right dielectric, its shape, thickness, and operating voltage parameters (it can be different, like the design of the device).

In addition, industrial or domestic operating conditions for a complex electrical device can have a significant impact on the quality of insulators. The insulation quality, thickness and electrical resistance must be consistent with the actual environmental influences and standard operating conditions.

To check the insulation properties, a test voltage is applied through the cable, and then with the help of a multimeter or tester, read the insulation resistance of the electrical device

Information on how to check the voltage in the electrical outlet is contained in next articlewhich we recommend that you familiarize yourself with.

The composition of electrical insulation can include both a certain thickness of the dielectric layer and a structural form (housing) made of a dielectric material. The dielectric covers the entire surface of live parts of the equipment or only those live parts that are isolated from other parts of the structure.

Types of insulating materials

Manufacturers producing modern electric switches that are used in residential, office and industrial buildings, distinguish the following types of electrical insulation: working (main), additional, double, reinforced.

Working (main) isolation

This, in essence, is the main protection of electrical installations, which provides them with normal and stable operation, without causing short circuits, protects consumers from direct contact with live parts.

According to the standards, working insulation must cover the entire surface of wires, cables, other elements through which electric current passes. For example, the cords of electrical appliances are always coated with insulation.

Polyvinyl chloride tubing is used as an inexpensive and quick way to isolate live parts of wires suitable for electrical appliances

It must guarantee stability against all potential, external influences that may occur during the operation of electrical switches in the event of simultaneous exposure to force fields, thermal heating, mechanical friction, and aggressive manifestations of the environment.

The listed factors negatively affect the electrical characteristics of dielectric (insulating) materials, and also because of them an irreversible deterioration of useful qualities can occur, that is, the insulation will undergo rapid wear.

Inexpensive and affordable insulation material. Made of PVC, it has different sizes both in length and in width. The color scheme can be different, the adhesive composition is resistant, the adhesion is strong and resistant to abrasion

If we are talking about the industrial operation of circuit breakers, the enterprise personnel should periodically check the wear rate of insulating structures, and take timely preventive measures to control their protective properties.

Responsible maintenance of a high level of insulation resistance reduces potential short circuits to the ground, the housing, reduces to zero electric shocks.

The resistance indicator characterizes the current state of insulation quality between 2 conductive elements, gives an indication of the risk of current leakage. The gentle, non-destructive nature of this control is useful in tracking wear and aging of insulation layers.

In small, low-branched power grids, insulation resistance is a major safety factor. The control of the main insulation can be carried out immediately after installation or repair, or periodically, carried out during operation of the equipment at least 1 time per year.

In very humid workshops, monitoring is carried out 2 to 4 times a year in a continuous mode. Measurements are performed with a digital measuring device for insulation control - a megaohmmeter.

The measuring device is universal. It is intended not only as a determinant of the actual state of insulation resistance, but also to test its electrical strength. With it, experts test the insulation layers of equipment for breakdowns of electricity

Periodic monitoring of insulation resistance at installed circuit breakers is carried out at production sites where equipment is exposed to the negative effects of corrosive fumes of chemicals, moisture, dust and elevated temperatures over time. In this case, the insulation of the circuit breakers may be violated. Devices with damaged insulation are dangerous to human life.

Industry PUE (Electrical Installation Rules), adopted in Russia, require regular measurement of the insulation resistance readings, which are present in power supply networks from 1 kV and above.

The resistance of dielectric materials in the network of lighting installations in the area between 2 adjacent fuses, between any wire and ground, and also between any two wires should not be ＜ 0.5 MΩ.

This indicator is not applicable in practice to the overhead wires of external electrical devices, to installations that are located in extremely humid rooms, because the resistance in them is unstable and depends on the indicators of air humidity.

It should be specially noted that if there are no standards for insulation for such installations, then such a factor should be taken into account by management of enterprises and take all measures for the safe operation of devices and more closely monitor the current state of insulation materials.

If you use a power tool with double insulation in your work, you will need to test its insulation with a megohmmeter every month. If the tool is handed out to employees at the enterprise, then a check for a short circuit to the housing should be performed with a special device - a multimeter

According to the PUE, the measurement of electrical insulation resistance should be carried out with a voltage of at least 500 V, and the insulation test of multicore cables with a voltage of 6-10 kV.

At least 2 people should determine the integrity of current-carrying cable conductors, check with a megohmmeter for their compliance with the phases. The rules require that one of them must have a permit not lower than group IV, and the second: not lower than group III.

Reasons for additional protection

Additional insulation is placed in electrical installations having an operating voltage of up to 1 kV. This is an independent insulation that will be installed together with the main insulation of the equipment in order to protect the circuit breakers in difficult and dangerous cases of operation by indirect contact with damaging elements.

Mainly, it performs the function of counteracting electric shocks if damage to the main insulation layer occurs. A practical example of additional insulation is the plastic housing of the circuit breaker, bushings, insulators, cambrics, plastic tubes and other types of dielectrics.

For this type of insulation, materials are used that differ in their physical properties from standard forms of dielectrics, which are the main insulation of electrical appliances.

To impregnate glass lacquer, varnishes are used on an oil, polyester, polyester-epoxy, silicon-organic basis or with the use of fluoroplastic or rubber. All of them perfectly create varnish, dielectric surfaces on the fabric.

This is done taking into account the fact that even in the most adverse operating conditions or methods of storage of electrical equipment, damage to the main, working and additional insulation at the same time would be unlikely.

The advantage of double insulation

Such potential danger to people as electric shock at the moment of indirect contact with equipment elements can be significantly reduced by installing double insulation.

These durable protective materials are used in electrical devices where there is voltage up to 1 kV. Here they put 2 degrees of protection - primary and secondary. Manufacturers install double insulation in various electrical devices: hand-held lamps, hand-held electric tools, in isolation transformers.

Many types of circuit breakers are in operation, which according to GOST must have both double and reinforced insulation, the specific case depends on the complexity of the production technology

The practical meaning of double insulation lies in the fact that in addition to the main, dielectric layer. place the second insulating layer on the live parts of the switches. It protects a person from touching a metal, conductive current that may well be under high voltage.

To avoid this, the metal cases of high-tech electrical equipment are covered with a layer of insulator, handles, buttons and control panels are made on the basis of dielectrics.

In household appliances, buttons, wires and a housing made of metal are also insulated. The disadvantage of this type of coating is considered to be relatively high mechanical fragility: there is a theoretical possibility of destruction of the insulating layer from repeated mechanical stresses.

Because of this, metallic, non-conductive parts of electrical devices may be energized. Therefore, it is very important to measure the physical state of the insulation with appropriate devices, in accordance with the electrical circuit.

Schematic diagram of the electrical circuit shown for measuring current leakage in insulation, according to GOST IEC 60335-1-2008, taking into account the needs of the national economy of the Russian Federation

It should be noted that the destruction of the second insulation layer will not be able to affect the main operation of the devices and, as a rule, is not detected at the time of verification. Double insulation makes sense to apply for those types of electrical equipment that in household use will not be subjected to mechanical shock and pressure on live parts.

The most reliable protection for people will be provided by a double insulation method on the equipment in which the case is made of non-conductive, insulating material: it serves as a guarantee against dangerous electric shock.

The non-conductive case of the devices will protect against current not only during breakdowns of the dielectric inside the product, but in case of accidental contact of a person with current-carrying elements. In case of destruction of the case, the structural arrangement of parts and elements will be violated, and the device will stop working.

If there is protection in it, then it will work automatically and disconnect the faulty product from the network. In the metal casing of the devices, the function of additional insulation is performed by special bushings.

Through them, the network cable passes into the housing, and insulating gaskets separate the equipment motor from the housing. The nameplate of an electrical appliance with double insulation carries an image of a special sign: a square inside another square.

What is reinforced insulation for?

In production conditions, there are times when double insulation is quite problematic to use according to the design features of electrical devices. For example, in switches, brush holders, etc. Then you have to use a different type of protection - this is reinforced insulation.

Reinforced insulation is placed on electrical installations with a rated voltage of up to 1 kV. It is able to provide such a degree of protection against electric shock that is equivalent to the properties of double insulation.

According to the requirements of GOST R 12.1.009-2009 SSBT, reinforced insulation can have several layers of dielectric, each of which cannot be tested separately for a breakdown of a short circuit, but only in the whole form.

Compliance of insulation with regulatory requirements for limit values ​​established as a result of testing. The procedure and limit values ​​are regulated by GOST IEC 60335-1-2008

Natural and synthetic dielectrics

Insulating materials, and otherwise, dielectrics, by their origin are divided into natural (mica, wood, latex) and synthetic:

• polymer and film insulators and tape;
• electrical insulating varnishes, enamels - solutions of film-forming substances made on the basis of organic solvents;
• insulating compounds in liquid state hardening immediately after application to conductive elements. These substances do not contain solvents, according to their purpose they are divided into impregnating (processing windings of electrical appliances) and casting compounds, which are used to fill cable couplings and cavities of devices and electrical units for sealing purposes;
• sheet and roll insulation materials, which consist of non-impregnated fibers of both organic and inorganic origin. It can be paper, cardboard, fiber or fabric. They are made of wood, natural silk or cotton;
• varnished fabrics with insulating properties - special plastic materials on a fabric basis, impregnated with an electrical insulating composition, which after hardening forms an insulating film.

Synthetic dielectrics have important electrical and physico-chemical characteristics that are important for the reliable operation of the devices, given by the specific technology of their production.

They are widely used in modern electrical engineering and the electronics industry to market the following types of products:

• dielectric sheaths of cable and conductor products;
• frames of electrical products such as inductors, housings, racks, panels, etc .;
• elements of wiring accessories - distribution boxes, sockets, cartridges, cable connectors, switches, etc.

Radio-electronic printed circuit boards are also produced, including panels used for the alignment of conductors.

Classification of insulation materials

Electrical insulation in household appliances is divided into the corresponding classes:

• 0;
• 0I;
• I;
• II;
• III.

Devices with insulation class “0” have a working insulating layer, but without the use of grounding elements. In their design there is no clamp for connecting the protective conductor.

Devices with class “0I” insulation have insulation + an element for grounding, but they contain a wire for connecting to a power source that does not have a grounding core.

The insulation is specially labeled. Grounding is indicated as a separate icon at the conductor connection point. This is done in order to equalize potentials. The yellow-green conductor is attached to the contacts of the socket, chandelier, etc.

Devices with class “I” insulation contain a 3-core cord and a plug with 3 contacts. Wiring devices of this category are subject to installation with grounding.

Electrical appliances that have Class II insulation, that is, double or reinforced, are often found in domestic use. Such insulation will reliably protect consumers from electric shock if the main insulation is damaged in the device.

Products equipped with durable double insulation are indicated in power equipment by the sign B, meaning: "insulation in isolation." Devices containing such a sign must not be earthed and grounded.

All modern electrical appliances having class “III” insulation can carry out their work in power networks, where there is a rated voltage of no higher than 42 V.

Absolute safety when activating electrical equipment is provided proximity switches, with the features of the device, the principle of operation and the types of which will familiarize us with the article recommended by us.

Conclusions and useful video on the topic

The video contains instruction on using the popular brand of megaohmmeter:

A small video review of insulating materials and methods of protecting current-carrying parts of wiring accessories:

Special types of insulation are used in the equipment of industrial switches, for example, air or oil type. In everyday life they are not used. If you had to deal with a violation of the insulation of circuit breakers at the factory, you should contact the specialists who service electrical installations.

Please write comments in the block below. Share useful information on the topic of the article, which is useful to site visitors. Ask questions on controversial and obscure points, post photos.