What kind of electric oven is safe
In daily life, the method of making staple food is nothing more than steaming, frying, boiling, roasting, and baking. The “roasting” of the staple food is not only used in the food and beverage industry, but also in the food processing industry. Toasted foods use ovens and charcoal ovens are almost extinct. The largest amount of gas ovens and fuel ovens currently used in restaurant kitchens and food factories are electric ovens. Compared with other ovens, electric ovens do not pollute the environment, are easy to install and use, and improve the working conditions of operators, and are therefore very popular. However, as an electrical product, if the electric oven is not properly installed, installed, or used, it will turn into an electric tiger, which may endanger the safety of personal and property. In recent years, malignant accidents such as electric shocks and fires caused by electric ovens have occurred from time to time.
China has implemented a production license system for food electric ovens since the 1980s. In 1997, it also issued new product safety standards. It has conducted numerous national supervision and inspections of food electric ovens to improve product quality and protection. People's lives and property security. In the second quarter of 2003, AQSIQ again organized a national supervision and random inspection of food electric ovens. The total product qualification rate was only over 60%. The safety situation of food electric ovens is still not optimistic.
What kind of electric oven is safe? According to some important regulations of national standards, combined with our quality problems found in the national supervision and spot checks and analysis of product safety accidents over the years, we briefly introduced several major safety requirements for electric ovens.
Protection against electric shock
Protection against electric shock is also called "protection against touching live parts". This requires that all live parts on the product should be closed, covered with a shell, cover, lid or insulating material, and these protective shells cannot be opened or removed without the use of tools at hand to prevent users Accidental contact with live parts caused by electric shocks when operating, moving or maintaining the electric oven.
During the inspection, it was found that in order to save labor and materials, some factories use the baffles to cover exposed live parts such as the ends of the electric heating tubes of the oven, but they cannot be seen by the eyes. Fingers can still be used from the bottom of the baffle or through the gaps and holes. Touched live parts; some for later factory maintenance and replacement of parts is convenient, electrical door is designed to be readily opened, the panel of the thermostat and other electrical components can be disassembled by hand, so that live parts exposed protection; other products use Bare heating wire as a heating element, but did not take any protective measures. The owner of these factories subjectively believes that users know where the electric ovens are and they will not touch them. This is wishful thinking. Such items of product protection against electric shock cannot meet the eligibility requirements and will cause serious insecurity to users and users.
Insulation resistance, leakage current and electrical insulation strength
For the prevention of personal electric shock, it is obviously not sufficient for the product to have protective measures that the guarantor cannot touch the live parts. The product should also ensure that the electrical insulation between all surfaces of the electric oven that can be reached by the person and the internal live parts is safe and reliable. , otherwise people may touch the non-charged enclosure of the oven still may be dangerous. Check whether the electrical insulation meets the requirements, and generally use the three indicators of insulation resistance, leakage current and electrical insulation strength. The instrument used for measuring the insulation resistance (commonly known as “Maniometer”) is inexpensive and easy to use. Therefore, in electric oven manufacturers, the method of measuring the insulation resistance is widely used to determine the quality of the electrical insulation of the product. This is a normal check by the user. It is a simple and practical method for whether the electrical insulation of the oven is damaged. However, in the GB4706 series of national mandatory safety standards, it is stipulated that the leakage current and electrical insulation strength are used as the basis for judging the electrical insulation quality of electric ovens.
Leakage current: When any electrical product is in use, if the hand of a person standing on the ground touches an ungrounded product, current will flow from the body. This current is called leakage current. Under normal circumstances, the leakage current of electrical products is very small, and people do not feel it. However, when the insulation medium is exposed to moisture and high temperature, the leakage current may exceed the safety value and personal electric shock accidents may occur. In order to prevent this danger, special instruments must be used to simulate human and environmental conditions and the product's leakage current should be tested to confirm that it does not exceed the specified limit.
Electrical insulation strength: also known as electrical strength or dielectric strength, commonly known as high pressure. China's mains supply voltage is single-phase 220V, three-phase 380V, but due to inductive loads and other reasons, the power grid under certain conditions may instantaneously generate over-voltage which is much higher than the supply voltage, which requires the electrical insulation of the product to have Certain ability to withstand over-voltage. The ability of electrical insulation to withstand breakdown voltage is called electrical insulation strength and is an important indicator for assessing the safety and quality of electrical insulation. The test method is to use a special high-voltage tester to apply a high test voltage between the live parts of the electric oven and the shell, and to maintain a certain time, observe whether the insulation breakdown or flashover. According to the different insulation properties, the test voltage value is generally 1000V to 3750V.
Long-term placement of electric oven does not cause insulation damp, or long-term high temperature continuous use of insulation caused by overheating, is the most easy to make electrical insulation performance decline, causing leakage, breakdown of the two extreme state. Therefore, leakage current and electrical insulation strength tests must be conducted separately under the conditions that simulate the two worst-case conditions. A test that simulates a wet state is generally called a cold state or a wet state; a test that simulates an overheat state is called a hot state or an operating temperature. All electrical insulation of the product should be able to withstand the full cold and hot state of the prescribed test before it is considered to meet the qualification requirements.
The insulation of the food electric oven heating pipe is the weakest link of the entire product electrical insulation, leakage, breakdown often occurs in these parts. In addition, the use of inferior thermostats, switches, and wires, the use of insulating materials with poor heat resistance, the use of hygroscopic asbestos, and silicate wool as electrical insulation, all contribute to the thermal or cold leakage current of the product, and electrical Insulation strength can not meet the requirements of qualified, and even cause an important reason for personal safety accidents. Strictly controlling the procurement of electrical components involving safety, and making inspections of key components such as electric heating pipes, is an important part of greatly improving the safety and quality of electric ovens.
Grounding measures
For the food electric oven, the so-called grounding measure is to install a grounding electrode (grounding bolt) on the metal shell body of the product, and then all other exposed metal parts that are not touchable with the body by hand, whenever possible, all Reliable connection to the grounding pole with a wire; the power cord must be provided with a protective wire of yellow and green color, the inner end of the wire is connected with the grounding pole on the main body of the metal shell reliably, and the outer end is connected with the grounding pole of the power plug; The oven with the plug is connected to the protective ground of the power supply during installation. The electric oven with reliable grounding of the metal shell can stand on the ground and touch the metal shell of the oven when the insulation fails and the shell has a dangerous voltage, because the oven shell is equal to the earth potential (the potential difference is equal to zero and there is no voltage) People do not pose any danger.
It can be seen that the electrical insulation and grounding of the electric oven constitute a double protection measure against personal electric shock. Double protection is an important safety principle in the national standard of GB4706. Throughout the standard clauses, it has greatly improved the safety of food electric ovens and has important practical significance.
In addition, we can also say that grounding measures are the last protective barrier against electric shock. Almost 100% of all accidents involving electric shocks have not been reliably grounded. There are three reasons: First, the product does not meet the requirements of the grounding electrode and protective ground wire; Second, the product grounding measures meet the requirements, but the field installation is not connected to the power of the protective ground wire; Third, the product installation site power system does not have protective ground wire ,unable to connect. The key to solving the first and second points is that product producers and users must truly understand that grounding is a matter of life and human nature. We must strictly implement the standards and be sloppy. The third point relates to the problems of the design and installation standards of civil building electrical systems and the matching of electric ovens and other electrical product standards, which are more complicated. But to be sure, ungrounded electric ovens can never be used.
Abnormal work
Abnormal work is a very important set of safety items for food electric ovens. Whether or not the products can still guarantee the safety of users and users in the event of human error or some kind of malfunction in the process of using the product? No accidents such as electric shocks or fires will occur.
Abnormal work is relative to normal work. For example, an electric oven is generally equipped with a set of temperature control system which automatically turns the heating element on and off to control the food baking temperature when the oven is in a normal operating state. Once the temperature control system fails to automatically cut off the heating power, the oven is in an abnormal state of operation, the heating is out of control, the temperature inside and outside the furnace rises without limit, and eventually the oven is burned or even caught fire. Some ovens are equipped with manual temperature control function. According to the operation regulations, the operator must not leave when using manual temperature control. However, an operator may inadvertently perform an erroneous operation, which may also result in an abnormal operating condition in which the heating is out of control. This requires that the oven should be equipped with a set of overheating protection system that is independent of the temperature control system. In case of temperature failure, the heating power can be quickly cut off to prevent a disastrous accident.
Electric ovens must guarantee the safety of people and the environment under normal working conditions, and also guarantee the safety of people and the environment under abnormal working conditions. This is another important safety principle of the GB4706 series of standards, which has extremely important practical significance for improving the safety and quality of electric ovens.
To achieve non-normal work safety protection must increase product costs, those who rely on the price of low-quality products to compete in the market can not be installed overheating protection system, there are some factories with poor quality parts look like, simply do not achieve the purpose of overheating protection. All of these food electric ovens that do not have overheating protection functions are non-conforming products that do not meet the national mandatory standards. There are serious potential safety hazards, and consumers should not purchase them at a low price. If such an unqualified product is used and an accident occurs, it will result in damage and the law will be used to protect its legitimate rights and interests.