Electrical safety of the hottest hand-held electri

2022-08-24
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Electrical safety of hand-held electric tools

hand held electric tools can be divided into three categories according to the protection against electric shock

the protection against electric shock of class I tools not only relies on basic insulation, but also has an additional safety protection measure, such as protective grounding, so that the accessible conductive parts will not become electrified when the basic insulation is damaged

the protection against electric shock of class II tools not only depends on basic insulation, but also includes additional safety protection measures (but does not provide protective grounding or do not depend on equipment conditions), such as double insulation or reinforced insulation. Its basic types are: ① insulating material shell type, which has a solid and basically continuous insulating shell; ② Metal shell type, it has a basically continuous metal shell, all of which use double insulation. When the application of double insulation is not feasible, which must be the simplest and most basic thing, it uses reinforced insulation; ③ Combined type of insulating material and metal shell

class III tools rely on safety extra low voltage for power supply. The so-called safety extra low voltage means that the voltage between phase lines and phase to ground does not exceed 42V, and is powered by safety isolation transformer

with the widespread use of hand-held electric tools, the importance of their electrical safety becomes more prominent. The user department shall formulate corresponding safety operation procedures for hand-held electric tools in accordance with national standards. The contents shall at least include: the allowable use range of tools, correct use methods, operation procedures, inspection parts and items before use, possible hazards and corresponding protective measures during use, storage and maintenance methods of tools, precautions for operators, etc. In addition, safety technology education and training should also be carried out for the use, maintenance and repair personnel, and attention should be paid to the inspection, use and maintenance supervision of hand-held electric tools to prevent vibration, moisture and corrosion

before use, hand-held electric tools should be selected appropriately. In general workplaces, real-time data collection and testing system should be possible. During the experiment, the friction force is transmitted to the pressure sensor through the lever. Class I tools can be used. When using class I tools, leakage protector and isolation transformer shall be equipped. Class II or III tools should be used in wet places. If class I tools are used, leakage protectors with flat action current of no more than 30 A and action time of no more than 0.1s must be installed on all layers of the cover. When working in boilers, metal containers and pipelines, class III tools or class II tools equipped with leakage protectors should be used. The action current of leakage protectors should not be greater than 15 A and the action time should not be greater than 0.1s. Tools with corresponding protection grade and safety technical requirements shall be used in special environments, such as hot and humid, rain and snow, and working environments with explosive or corrosive gases

when installing and using, the safety isolation transformer of class III tools, the leakage protector of class II tools, the control box and power supply device of class II and III tools should be far away from the workplace

the power lead of the tool shall be tough rubber wrapped wire or plastic sheathed soft copper wire, without joints in the middle, and shall not be arbitrarily extended or replaced. The protective grounding resistance shall not be greater than 4. During operation, the protective cover of the running parts shall not be removed, and the tools and abrasives shall be stopped when they are replaced

there should be guardians in narrow workplaces

except that 36V and below voltage is used, the secondary winding of the power supply isolation transformer is not grounded, and the power circuit is equipped with a reliable low-voltage leakage protector, the rest should wear rubber insulating gloves, and if necessary, wear insulating shoes or stand on an insulating pad. The operation isolation transformer should be the original and auxiliary double winding, the auxiliary winding should not be grounded, and the metal shell and iron core should be reliably grounded. The wiring terminal shall be enclosed or shielded. The original winding shall be equipped with a fuse and controlled by a bipolar knife switch. The lead length shall not exceed 3M and there shall be no joints

before and after the use of the tool, the keeper must carry out daily inspection, and the user should carry out inspection before use. The contents of daily inspection include: whether the shell and handle are damaged and cracked, whether the mechanical protective device is intact, whether the rotating part of the tool is flexible, light and unimpeded, whether the electrical protective device is good, whether the protective wire connection is correct and reliable, whether the power switch is normal and flexible, and whether the power plug and power wire are intact. If problems are found, they should be repaired or replaced immediately

at least once a year, full-time personnel should check it regularly. In areas with frequent changes in humidity, heat and temperature, or places where the loading curve and maximum tension can be used and recorded, the inspection cycle should be shortened accordingly. In addition to the above checks, 500V megger should also be used to measure the insulation resistance of the circuit to the shell. The insulation of tools that are not used for a long time must also be tested before use. Class I tools should be less than 2m, class II tools should be less than 7m, and class III tools should be less than 1m; Otherwise, it should be dried or repaired

the maintenance of tools should be carried out by a specially designated maintenance department, equipped with necessary inspection equipment and instruments. Do not arbitrarily change the original design parameters of the tool, do not use substitute materials with lower performance than the original, and do not replace parts that do not conform to the original specifications. The insulating gasket and sleeve in the tool shall not be omitted or removed arbitrarily

the insulation shall be measured after maintenance, and the voltage withstand test shall be carried out between the live parts and the shell. The withstand voltage test voltage of class I tools isolated from live parts by basic insulation is 950v, that of class III tools is 380V, and that of class II tools isolated from live parts by reinforced insulation is 2800v

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