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A sudden fail-open fault can cause multiple secondary failures if it is fast and the circuit contains an inductance; this causes large voltage spikes, which may exceed 500 volts. A broken metallisation on a chip may thus cause secondary overvoltage damage. [1] Thermal runaway can cause sudden failures including melting, fire or explosions.
Metal-oxide varistor manufactured by Siemens & Halske AG. Modern varistor schematic symbol, which is the same as a thermistor symbol [1]. A varistor (a.k.a. voltage-dependent resistor (VDR)) is a surge protecting electronic component with an electrical resistance that varies with the applied voltage. [2]
Overheating is a phenomenon of rising temperatures in an electrical circuit. Overheating causes damage to the circuit components and can cause fire, explosion, and injury. Damage caused by overheating is usually irreversible; the only way to repair it is to replace some components.
A thermistor is a semiconductor type of resistor in which the resistance is strongly dependent on temperature. The word thermistor is a portmanteau of thermal and resistor.The varying resistance with temperature allows these devices to be used as temperature sensors, or to control current as a function of temperature.
Another type of thermal switch is a PTC (Positive Temperature Coefficient) thermistor; these thermistors have a "cutting off" temperature at which the resistance suddenly rises rapidly, limiting the current through the circuit. When used in conjunction with a thermistor relay, the PTC will switch off an electrical system at a desired temperature.
The high temperatures can also cause the contact metals to more rapidly oxidize and corrode. Contacts reach end of life for one of two reasons. Either the contacts fail to BREAK because they are stuck (welded) closed, or the contacts fail to make (high resistance) because of contact corrosion or because excessive material is lost from one or ...
The temperature of the resulting electric arc is very high (tens of thousands of degrees), causing the metal on the contact surfaces to melt, pool and migrate with the current. The high temperature of the arc causes dissociation of the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc energy slowly destroys ...
A resettable fuse or polymeric positive temperature coefficient device (PPTC) is a passive electronic component used to protect against overcurrent faults in electronic circuits. The device is also known as a multifuse or polyfuse or polyswitch .