Summary of this question: in daily work, hand-held power tools are required in many cases, but often operators do not know how to choose power tools with different levels of protection, or the measures taken cannot meet the safety requirements. Therefore, everyone needs to master its classification and requirements for use.
Classification of hand-held power tools and precautions
01 Simply put
Class I: In addition to basic insulation, zero protection is also required for protection against electric shock.
Category 2: The tool itself is double or reinforced insulated and does not require a protective earth connection.
Third category: Powered by a safety extra-low voltage power supply, and the tool does not generate a voltage higher than the safety voltage of the power supply inside the tool.
02 professional lecture
1. Tool class
The tool not only uses basic insulation to protect against electric shock, but also incorporates additional precautions by connecting accessible conductive parts to a protective (earth) conductor in an installed fixed circuit, connected in such a way that accessible conductive parts are not energized in case of breakdown of the main insulation.
2. Second Class Tools
Its rated voltage exceeds 50V. Tools not only rely on basic insulation to protect against electric shock, but also provide the additional safety measures of double insulation or reinforced insulation and measures without a protective earth or depending on installation conditions. For this type of tool, there are two types of metal and non-metal bodies, but the hand part is non-metal, and there is a "back" symbol on the non-metal part.
3. Three types of tools
Its rated voltage does not exceed 50V. When powered by an extra-low voltage power source, no voltage above safety extra-low voltage is generated inside the tool. All of these tool cases are plastic.
03 place of use
1. Class I or Class II hand power tools can be used in general places where the air humidity is less than 75%, and the number of connection points between the metal case and the PE line must be at least 2; The rated operating leakage current of the leakage protection device in the box should not exceed 15mA, the rated leakage response time should not exceed 0.1s, and the load line plug should have a special protective contact. The sockets and plugs used must be unified in design, and the simultaneous use of current-carrying and protective contacts should be avoided.
2. For work in wet areas or on metallic structures, class II or class III tools powered by safety isolation transformers should be used. When using hand-held power tools with a class II metal case, the number of connection points between the metal case and the protective earth line must be at least 2, the rated leakage current of the leakage protection device in the corresponding junction box must not exceed 15 mA, and the estimated leakage time must not exceed 0.1 s, the load line plug must have a special protective contact, the used socket and plug must be of the same design, the simultaneous use of current-carrying and protective contacts should be avoided; junction box and control unit must be installed outside the workplace. Do not use Class I hand-held power tools in wet areas or on metal racks.
3. In narrow places (such as boilers, metal containers, metal pipes, etc.), it is necessary to use a handClass III power tools powered by safety isolation transformers, and a junction box and safety isolation transformers must be installed. outside bottlenecks. And connect the PE line. Leakage protection devices shall be splash-proof, their rated operating leakage current shall not exceed 15 mA, and their rated leakage response time shall not exceed 0.1 s. During the operation, someone has to watch from the outside.
04 Precautions
1. Body, handle, weight, plugs, switches, etc., must be intact before using hand-held power tools. An idle test must be performed before use. Can only be used if certified or with acceptance procedures. The equipment is marked as certified.
2. When using Class I hand tools, you must wear insulating clothing or stand on insulating mats if necessary. And make sure there are good zero connection or grounding measures, the zero protection line is separated from the working zero line, and the zero protection line uses stranded annealed copper wires with a diameter of 1.5mm or more. The leakage current of the leakage protection device must not exceed 15mA, and the operation time must not exceed 0.1s.
3. To ensure safety in public areas, class II tools should be used, and an anti-leakage device with a leakage current rating of 15mA or less and a trip time of 0.1s or less should be installed. The insulation resistance of class II instruments must be at least 7 MΩ.
4. Class II or Class III tools must be used outdoors, in damp locations, or on metal structures, and splash guards must be installed to prevent leaks. The use of Class I hand power tools is strictly prohibited.
5. In narrow places (boilers, metal containers, trenches, pipelines, etc.), class III hand-held power tools with isolation transformers should be used. Isolation transformers and leakage protection devices are installed outside bottlenecks and must be supervised during operation. ,
6. For loading hand-held power tools, weather-resistant soft cables with a rubber sheathed copper core must be used, and there must be no connectors.
7. Power tools should not change the plug arbitrarily during use, let alone plug the wire directly into a socket without using a plug. When the power tool is not in use or the work head needs to be replaced, disconnect the plug in time. When inserting the plug, the switch must be in the off position to prevent sudden switching on.
8.Check frequently during use.If you find problems such as broken insulation, broken power cord, orcable jacket, ground wire detachment, socket cracking, poor contact and intermittent operation, stop the machine immediately for repairs. When moving an electric tool, you must hold the handle of the tool, and you cannot use the rubber cord to move the tool, and always pay attention not to scratch, cut, or damage the rubber cord to avoid accidents. .
9. For power tools that have not been used for a long time, before use, it is necessary to measure the insulation resistance value between the winding and the body with a 500 V megger. It should not be lower than 7 MΩ, otherwise it must be dried.
10. Power tools are not suitable for use in special environments containing flammable, explosive or corrosive gases and moisture and must be stored in a dry, clean and non-corrosive atmosphere. For motors and electrical appliances with non-metallic housings, contact with solvents such as gasoline should be avoided during storage and use.