However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. A strong current surges through the earth wire because it has a very low resistance.
This breaks the fuse and disconnects the appliance. In this scenario, the electricity has effectively chosen to travel through the path of least resistance. It is just the law of big numbers. With the current traveling through the earthing wire, the low resistance of the earthing wire will cause a high current flow. The high current flow will cause a fuse to be blown or the ECLB to be tripped. Typically an equipment has a switch that is used to turn it on. If the wire touched the case at location that is on the other side of the switch it cannot short the connection before the person touches the equipment.
Also there may be a problem that occurs only in certain situations. How is the current not high enough to melt the fuse while the resistance of the circuit is too low and current is infinite. My doubt is in this part: The current is not high enough to trigger the breaking of fuse in the power plug. If you have a live chassis situation on an unearthed piece of equipment there is nothing to take the current to ground so the power will stay on the chassis.
A persons body has a high resistance compared to a wire. Notify me of follow-up comments by email. Notify me of new posts by email. Consider this scenario: The live wire is frayed and touched the metal casing of the appliance. Another phrase for this is: The metal casing of the appliance becomes live. A Class II or double insulated electrical appliance is one which has been built in such a way that it does not require a connection to electrical earth ground. A double insulated appliance displays the symbol above; the square inside a square symbol refers to 2 layers of insulation, thus double insulation.
The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing.
This is usually achieved at least in part by having two layers of insulating material surrounding live parts or by using reinforced insulation. In the United Kingdom, a double insulated appliance must be labelled Class II , double insulated , or bear the double insulation symbol a square inside another square.
Double insulation construction of appliances and tools allows the manufacturer to produce a lower-cost product. Double insulated appliances and tools are generally found around the home while their grounded counterparts are more likely to be found in commercial and industrial operations where they encounter much rougher treatment and more potential for damage. English Spanish.
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