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Forum Index Profile for :: AlexDdfsdfsdfsd Avatar All about AlexDdfsdfsdfsd Ranking: Unripe member Registration date: 16/02/2022 17:07:53 Number of messages posted: No posted messages available Created topics: No topic created Biography: All electrical appliances using mains voltage have to provide at least 2 levels of protection to the user. This is to ensure that if one of the protection layers were to fail, there is the back-up of the second layer still in place. This makes electrical equipment very safe to use. Appliances can be Class 1 or Class 2. When PAT testing, it is important to first identify the Class of the appliance as Class 1 appliances are tested differently from Class 2 appliances. Depending on how exactly the protection is provided, electrical appliance are put into 5 Classes of equipment construction which are Class 1, 2, 3, 0, 01. Of these the most important are Class 1 & 2. For completeness all the Classes are described below. CLASS 1 Here the protection is provided by a combination of insulation and use of the mains Earth. It is best shown by referring to an electric fire that has been taken apart. In the open plug the three wires connecting to the LIVE, NEUTRAL and EARTH pins. Inside the fire, the brown LIVE wire and the blue NEUTRAL wire connect to a plastic connector. The green/yellow Earth wire connects to the metal case of the fire. The user is protected from electric shock by the plastic insulation of the connector. This holds the LIVE and NEUTRAL wires in place and prevents them from touching the metal case of this electric fire. This plastic insulation of the connector is known as basic insulation. If this basic insulation were to fail, say due to excessive movement of the cable where it touches the metal case then the user of the fire can receive an electric shock if not for the fact that the EARTH wire is present. By connecting to the metal case of the electric fire, the EARTH wire keeps all this metal at EARTH potential. What this means is that it is impossible to get an electric shock even when the metal case of the fire is connected directly to the LIVE voltage. In practice a fuse would blow either in the plug or the main fuse box to protect the user. In summary, in Class 1 appliances the user is protected by a combination of basic insulation and the provision of an EARTH connection, thus providing two levels of protection. When PAT Testing Class 1 appliances, the Earth Continuity and Insulation Resistance tests are carried out. https://linkhay.com/blog/232121/nguyen-ly-noi-com-dien-co-gi-dac-biet-cac-hang-noi-com-dien-tot-nhat-hien-nay CLASS 2 In a Class 2 appliance, the user is protected by at least two layers of insulation. For this reason, Class 2 appliances are also known as Double Insulated. They do not require an Earth connection. This is best shown by looking inside a Class 2 electric drill which has been opened up. Inside one can see that as well as the plastic connector providing basic insulation, there is additional insulation provided by the plastic enclosure of the drill. The user is therefore protected by two separate layers of insulation. When PAT testing Class 2 appliances, just the Insulation Resistance test is carried out. Class 2 appliances are always indicated by the double box symbol on the rating plate. https://twitter.com/dodiengiaree/status/1474776966599380994 CLASS 3 Equipment built to Class 3 standard are designed to be supplied from a special safety isolating transformer whose output is known as Safety Extra-Low Voltage or SELV. This must not exceed 50 V AC and is normally is below 24V or 12V. All Class 3 appliances are marked by a special symbol. There is no use of an Earth in Class III appliance The electrical safety of Class 3 appliances are taken care of in the safety isolating transformer design where the separation between the windings is equivalent to double insulation. The transformer is marked as being suitable for use with Class III appliances. https://dodiengiare.vn/nguyen-ly-noi-com-dien/ Contact AlexDdfsdfsdfsd Email Address: Private Message:

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