The safe operation of all types of electrical equipment depends directly on the actual condition of the insulation materials that are incorporated into the design of the live parts of each installation product. If the insulation of switches is faulty, electrical failure, fire or even accidents are possible.
We tell you all about the types of insulation that ensure the complete safety of using switching devices. In our proposed article we describe in detail natural and synthetic, conventional and reinforced versions. The particular marking and the tips for buyers are given.
The contents of the article:
- Insulation protection for electrical devices
- Stypes of insulating materials
- Operation (basic) insulation
- Reasons for supplementary protection
- Benefit of double insulation
- What is reinforced insulation for?
- Natural and synthetic dielectrics
- Classification of insulating materials
- Conclusions and useful video on the subject
Insulating protection for electrical installations
Insulating materials protect the surrounding people and animals against electric shocks. There is one condition: the dielectric material must be chosen correctly, its shape, thickness, operating voltage parameters (it may be different, as well as the design of the appliance).
In addition, the quality of insulators may be significantly affected by industrial or domestic operating conditions of a complex electrical appliance. The insulation quality, thickness and degree of electrical resistance must correspond to the actual environmental influences and the standard operating conditions.
In order to check the insulation properties a test voltage is applied over the cable and then the insulation resistance of the electrical device is read with a multimeter or tester
Information on how to check the voltage in an electric socket is given in the following article which we recommend.
Electrical insulation may consist of a certain thickness of dielectric layer as well as a structural form (housing) made of dielectric material. The entire surface of the equipment's live parts or only those live parts that are insulated from other parts of the structure are covered with dielectric material.
Stypes of insulating materials
Makers of modern electrical switches used in residential, office and industrial buildings distinguish between the following types of electrical insulation: working (basic), additional, double, reinforced.
It is in fact the main protection for electrical installations that allows normal and stable operation without short-circuits and protects consumers from direct contact with live parts.
Base insulation, according to regulations, must cover the entire surface of conductors, cables and other components through which current flows. For example, the cords of electrical appliances are always covered with insulation.
PVC tubes are used as an inexpensive and rapid method of insulating live parts of conductors suitable for electrical appliances
It must guarantee resistance against all potential, external influences which may occur during operation of electrical switches in case of synchronous action of power fields, thermal heating, mechanical friction, aggressive environmental manifestations.
The above-mentioned factors adversely affect the dielectric (insulating) materials' electrical properties, and irreversible deterioration of the useful properties can also occur because of them, i.e. the insulation is subject to rapid wear.
Inexpensive and available to everybody insulating material. It is made of PVC and is available in different sizes in both length and width. Available in various colors, the adhesive is strong, the bond is strong and resistant to abrasion
In the industrial operation of switches, the plant personnel must periodically check the wear rate of the insulating structures and carry out timely preventive measures to control their protective properties.
Responsible maintenance of a high level of insulation resistance reduces the potential for earth/ground/ground faults and reduces electric shocks to zero.
The insulation resistance value indicates the current state of insulation quality between 2 conductive elements, giving an indication of the risk of current leakage. The gentle, non-destructive nature of such testing is useful in monitoring wear and aging of insulation layers
In small, sparsely branched power grids, insulation resistance is a major safety factor. The basic insulation test is either an acceptance test, carried out immediately after installation or repair, or a periodic test carried out at least once a year, during the operation of the equipment.
In very humid workshops, the test is carried out 2 to 4 times a year on a continuous basis. The measurements are carried out with a digital megohmmeter, an insulation control meter.
It is a measuring, multi-purpose instrument. It is used not only to determine the actual condition of the insulation resistance but also to check its electrical strength. With it, specialists test the insulation layers of equipment for electrical breakdowns
Periodic insulation resistance tests on installed switches are performed at production sites where equipment is negatively affected by caustic chemical vapors, moisture, dust and elevated temperatures over time. At the same time, the insulation of circuit breakers can be damaged. Devices with damaged insulation are dangerous to human life.
The branch PUE (Electrical Installation Regulations Rules) adopted in Russia, require regular measurement of insulation resistance readings, which are present in the power supply networks of 1kV and above.
The resistance of the dielectric materials in the network of lighting installations between 2 adjacent fuses, between any wire and ground, and between any two wires must be not ＜ 0,5 Mohm.
This figure does not apply in practice to overhead wires of external electrical appliances, to installations which are in extremely damp rooms, because the resistance therein is variable and depends on the humidity of the air.
It should be particularly noted that if there are no insulation standards for such installations, this factor should be taken into account by plant management and all measures should be taken to operate the devices safely and to monitor more closely the current condition of the insulation materials.
If you use a double insulated power tool at work, then it is necessary to test its insulation monthly with a megohmmeter. If the tool is given to employees in the company, the insulation insulation test should be carried out with a special device - multimeter
According to PUE, the measurement of insulation resistance should be carried out at a voltage of at least 500 V, and the insulation test of multi-core cables at 6-10 kV.
Testing the integrity of current-carrying cable cores, checking them for phase compliance, should be carried out by at least 2 people. Regulations require that one of them must have at least Group IV approval and the other: at least Group III.
Causes of extra protection
Additional insulation is placed in electrical installations with operating voltages up to 1 kV. It is an independent insulation that will be mounted together with the main insulation of the equipment to protect circuit breakers in difficult and dangerous cases of operation by indirect contact with damaging elements.
Mainly, it has the function of resisting electric shocks if damage to the main layer of insulation happens. A practical example of supplementary insulation is the plastic switch body, insulator sleeves, kimballs, plastic tubes and other types of dielectrics.
In this type of insulation, materials that differ in their physical properties from the standard forms of dielectrics that are the basic insulation of electrical appliances are used.
Oil-based, polyester, polyester-epoxy, silicone-organic or fluoroplastic or rubber-based varnishes are used for impregnating glass cloth. They all create perfectly lacquered, dielectric surfaces on fabric
This is done in consideration of the fact that even in the most adverse working conditions or the way electrical equipment is stored, it would be unlikely that the main insulation, the working insulation and the supplementary insulation would be damaged at the same time.
The advantage of double insulation
The potential danger to persons, such as electric shock at the moment of indirect contact with pieces of equipment, can be greatly reduced by mounting double insulation.
These robust protective materials are used in electrical devices where voltages up to 1 kV are present. Two degrees of protection, basic and supplementary, are provided here. Double insulation is installed by manufacturers in various electrical devices: hand lamps, hand-held electrical tools, isolation transformers.
There are many types of switches in use that, according to GOST, must have both double and reinforced insulation, the particular case depends on the complexity of the manufacturing technology
The practical meaning of double insulation is that, besides the basic, dielectric layer. a second insulating layer is placed on the current-carrying parts of switches. It protects people from touching metal, current-carrying parts that could well be under high voltage.
To avoid this, the metal housings of high-tech electrical equipment are covered with a layer of insulator, handles, buttons and control panels are made of dielectrics.
In household appliances, buttons, wires and the housing shell, made of metal, are also insulated. A disadvantage of this kind of coating is the relatively high mechanical brittleness: there is a theoretical possibility that the insulating layer could be destroyed by repeated mechanical action.
This may lead to metal, non-current conducting parts of electrical devices becoming live. Therefore it is very important to measure the physical condition of the insulation with appropriate instruments according to the wiring diagram.
The basic circuit diagram given for measuring the insulation leakage current according to GOST IEC 60335-1-2008, taking into account the requirements of the Russian national economy
It should be noted that the destruction of the second layer of insulation will have no effect on the basic operation of the devices and it is usually not detectable at the time of testing. Double insulation makes sense for those types of electrical equipment that will not be subject to mechanical shocks and pressure on live parts in domestic use.
The best protection for people will be provided by the double insulation method on equipment with a housing made of non-conductive, insulating material: it serves as a guarantee against dangerous electric shock.
Conductive housing of appliances will protect against current not only by dielectric breakdown inside the product, but by accidental contact If the enclosure fails, the structural arrangement of the parts and elements will be disturbed and the device will stop working.
If there is protection in it, it will operate automatically and disconnect the faulty product from the mains. In the metal housing of the devices, special bushings serve as additional insulation.
The mains cable enters the housing through these, and insulating gaskets separate the electric motor of the equipment from the housing. The nameplate of a double-insulated electrical appliance bears a special symbol: a square inside a square.
What is reinforced insulation for?
There are times when double insulation is rather problematic to apply due to the design features of electrical devices. For example, in circuit-breakers, brush-holders, etc. A different kind of protection, reinforced insulation, must then be used.
Reinforced insulation is supplied for electrical installations with a rated voltage up to 1 kV. It is capable of providing a degree of protection against electric shock that equals the properties of double insulation.
According to the requirements of GOST R 12.1.009-2009 SSBT, reinforced insulation may have several dielectric layers, each of which cannot be tested separately for a short-circuit breakdown, but only as a whole.
Isolation compliance to regulatory requirements by limit values determined by testing. The procedure and the limit values are regulated in GOST IEC 60335-1-2008
Insulating materials, also called dielectrics, are divided into natural (mica, wood, latex) and synthetic ones according to their origin:
- polymer-based film and tape insulators;
- electric insulating varnishes, enamels - solutions of film-forming substances made from organic solvents;
- insulating compounds that solidify in the liquid state immediately after application to conductive elements. These substances do not contain solvents and are classified according to their purpose into impregnating (processing of windings of electric appliances) and filling compositions for sealing cable joints and cavities of devices and electric units;
- sheet and roll insulating materials consisting of non-impregnated fibers of both organic and inorganic origin. They can be paper, cardboard, fiber or fabric. They are made of wood, natural silk or cotton;
- lacquers with insulating properties are special plastic cloth-based materials impregnated with an electrical insulating compound, which forms an insulating film after curing.
Synthetic dielectrics have important electrical and physical-chemical characteristics for reliable device operation, set by a specific production technology.
These are widely used in the modern electrical and electronic industry to market the following types of products:
- dielectric sheathing of cable and conductor products;
- frames of electrical products such as inductance coils, housings, racks, panels, etc.
- electric fittings such as junction boxes, sockets, cartridges, cable connectors, switches, etc.
also produces radio electronic printed circuit boards, including panels used for wire stranding.
Classification of insulating materials
Electrical insulation in household appliances is divided into appropriate classes:
Facilities with insulation class \"0\" have a working insulation layer, but without the use of earthing elements. They do not have a clamp to connect a protective conductor.
Facilities with insulation class \"0I\" have insulation + earthing element, but they contain a wire to connect to a power source that has no earthing conductor.
The insulation is specially marked. The grounding is indicated by a separate marking at the connection point of the conductor. This is done to equalize potentials. A yellow-green conductor is connected to the contacts of sockets, chandeliers, etc.
Fixtures with class \"I\" insulation contain a 3-wire cord and a plug with 3 contacts. Electrical appliances in this category must be installed with a ground connection.
Electrical appliances with class \"II\" insulation, i.e. double or reinforced, are often found in domestic use. Such insulation will reliably protect consumers from electric shock if damage to the basic insulation occurs in the appliance.
Products furnished with strong double insulation are marked B in power equipment, signifying: \"insulated in insulation.\" Devices containing such a sign cannot be grounded or earthed.
All modern electrical appliances having class \"III\" insulation can perform their work in power supply networks where there is a nominal voltage not exceeding 42 V.
Automatically safe activation of electrical equipment is provided by non-contact switches, the features of their construction, operating principles and types of which will be introduced by our recommended article.
Conclusions and useful video on the topic
The video provides instructions on how to use the popular megohmmeter brand:
A short video overview of insulation materials and how to protect the current carrying parts of electrical installation fittings:
Special insulation types are used in industrial switchgear such as air- or oil-powered switches. They are not used at home. If you encounter a breaker insulation malfunction in the workplace, you should contact an electrician.
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