Insulation double

Also, reading up on the latest Inverters, many of them nowadays, for safety reasons, have their outputs completely Isolated from the Internal circuitry by having the Active and Neutral wires coming from a separate winding on a double Insulated ferrite core. 

Early work in the 1960s on thin-hlm EL (TEEL) involved the excitation of Al/ZnS (activated by Mn or Cu) deposited on glass, but the key step forward was taken when the double-insulator structure was developed as shown in Figure 3.30. As can be seen the ZnS film is sandwiched between two insulating layers, limiting the amount of charge transferred to the device and also totally encapsulating the phosphor film. In spite of this the EL device still suffered from lifetime problems and it was not until 1978, when Sharp demonstrated a 240 x 320 display, that this problem was overcome. 

A method of manufacturing the structure is also disclosed. In short, islets of HgCdTe are formed from an HgCdTe layer which has been formed on a CdTe substrate. Next, the double insulation layer and the metal layer are formed. The bumps are provided before the CdTe substrate is removed by etching. 

Thermal insulators comprise an equally broad range of materials. Such inorganics as mineral fibers, magnesia, aluminum silicate, cellulose, and glass fibers are widely used for steam and hot-water pipes, furnaces, and blown-in home insulation. Organic products that are effective include plastic foams (polyurethane, polyvinyl chloride, polystyrene) and cellular rubber. There are a number of materials that may be called double insulators, since they have both electrical and thermal insulating properties,... 

What if we have an exposed conductor that is not connected to earth (such as for equipment with a two-wire ac cord), or if earthing is itself not an acceptable level of protection for that particular type of equipment as per safety regulations Then, besides the layer of basic insulation, we need another insulating layer (with identical dielectric withstand capability). This is called supplementary insulation. Together these two layers (basic + supplementary) are said to constitute double insulation. We could also use a single layer of insulation, with dielectric withstand properties equivalent to double insulation (i.e. 3000 V ac or 4242 V dc). That would then be called reinforced insulation. So for example, if the equipment is by design, meant only for a two-wire ac cord, we would need two layers of approved insulators (or... 

Line-to-earth capacitors are called Y-capacitors. Since Y-caps are critical in terms of having the potential to cause electrocution if they fail, approved Y-caps are typically impulse-tested up to 5 kV peak. Note that Y-caps used anywhere on the primary side (in off-line applications) must always be safety approved. Depending on the location in the power supply, we may even need two Y-caps in series (basically corresponding to double insulation). However, sometimes we can also find Y-caps placed between the secondary ground and earth/enclosure (for EMI suppression purposes). In this position, it is usually acceptable to use any ordinary 500 V ac rated capacitor (unapproved). 

Insulated wires come as single-insulated thermoelements or double-insulated duplex wires. Duplex wires can be obtained with a stainless steel overbraid for wear and abrasion protection. Table 16.13 lists characteristics of insulations used with thermocouple wires. 

This type of equipment has two levels of insulation. The first level may be considered as being equivalent to that of Class 1 equipment. The first level is then completely surrounded by a second level of insulation so that no contact can be made between the phase conductors and the outer frame. Hence the protective device at the source of supply need not be involved in circuit disconnection when the first level insulation fails. This type of equipment is sometimes referred to as double insulation or doubly insulated equipment e.g. hand-held domestic electric drilling machines. This type of equipment is not considered in the following discussions and calculations. See also BS7430. 

In addition to their excellent dielectric properties, RPs provide necessary strength with reduced silhouette and weight. The corrosion resistant, smooth, hard surfaces also resist the embedment of contaminants. Since at least the 1940s utility companies have used components that include pole-top pins, adjustable tension braces, guy-strain insulators, line spacers, insulator pins, upsweeps, double-insulator standoff brackets, switch control rods, hot sticks, and switchgear components. 

Apparatus equipped with three-prong plugs or double-insulated... 

If the equipment utilizes only two wires for input (line and neutral), as a double insulated product, and there is no ground connection, it is then necessary to mark the product with the Class II symbol. Examples of rating labels for single phase products are ... 

Double insulation. Insulation comprised of both basic and supplementary insulation (provides two levels). 

Reinforced insulation. A single insulation system that provides a degree of protection against electrical shock equivalent to double insulation. It may comprise several layers to meet thickness and/or test requirements. 

The device may be grounded for safety reasons (safety class I, as shown in Figure 10.35, maximum resistance in the protective earth conductor between power plug and chassis 0.2 Q), or double insulated (safety class II). 

Double insulation of tools provides protection to the tool and the user, so that the tool cannot be charged in case of a fault. This barrier is defined as having two states PSB5 (-I-) Proper PSB5 (—) Improper. Success means that double insulation exists and is proper. Failure means that double insulation is improper and will not protect the tool in case of a fault. 

Earth bonding tests apply a substantial test current, typically about 25 A, down the earth pin of the plug top to an earth probe, which should be connected to any exposed metalwork on the portable appliance being tested. The PAT Tester will then calculate the resistance of the earth bond and either give an actual reading or indicate pass or fail. A satisfactory result for this test would typically be a reading of less than 0.1 n. The earth bond test is, of course, not required for double-insulated portable appliances because there will be no earthed metalwork. 

A flash test tests the insulation resistance at a higher voltage than the 500 V test described above. The flash test uses 1.5 kV for Class 1 portable appliances, that is, earthed appliances, and 3kV for Class 2 appliances, which are double insulated. The test establishes that the insulation will remain satisfactory under more stringent conditions but must be used with caution, since it may overstress the insulation and will damage electronic equipment. A satisfactory result for this test would typically be less than 3 mA. 

Information teohnology e.g. desktop oomputers, VDU soreens No Yes, 2-4 years No if double insulated -otherwise up to 5 years... 

Double-Insulated equipment not handheld, moved occasionally, e.g. fans, table lamps, slide projectors No Yes, 2-4 years No... 

Double-insulated equipment handheld, e.g. power tools Yes Yes, 6 months to 1 year No... 

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