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A light switch may cause a small, harmless spark when switched on or off. In an ordinary household this is of no concern, but if a flammable atmosphere is present, the arc might start an explosion. In many industrial, commercial, and scientific settings, the presence of such an atmosphere is a common, or at least commonly possible, occurrence.
In electrical engineering, a limit switch is a switch operated by the motion of a machine part or the presence of an object. A limit switch can be used for controlling machinery as part of a control system , as a safety interlock , or as a counter enumerating objects passing a point.
The primary concept behind intrinsic safety is the restriction of available electrical and thermal energy in the system so that ignition of a hazardous atmosphere (explosive gas or dust) cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that no significant energy storage is possible.
A sail switch might be used to protect a fan forced pellet stove, central heating system, electric heating element from being energized before the air flow from the blower is established. [2] Sail switches might also be used to alarm if a ventilation fan in a hazardous location fails and air flow has stopped.
The enclosure is the only part of the equipment which is seen by users. It may be designed not only for its utilitarian requirements, but also to be pleasing to the eye. Regulations may dictate the features and performance of enclosures for electrical equipment in hazardous areas, such as petrochemical plants or coal mines.
This would be hazardous for the operator. For this reason, many European, American, national and international norms and safety standards prohibit the use of simple relays or contactors on hazardous machines. [9] The typical design of a first-generation safety relay is based on the classic three-contactor combination.
The initiative was to limit the amount of hazardous chemicals in electronics. The RoHS 1 directive took effect on 1 July 2006, and is required to be enforced and became a law in each member state. [3] This directive restricts (with exceptions) the use of ten hazardous materials in the manufacture of various types of electronic and electrical ...
The classification given to a particular zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring and its persistence if it does. Equipment in use before July 2003 is allowed to be used indefinitely provided a risk assessment shows it is safe to do so.
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