Sparks and electrical arcs

Different values for the minimum ignition energy are obtained in low voltage circuits with an ohmic (R) and inductive (L) load. As a switching element, a spark test apparatus with counter-rotating tungsten wires and a cadmium 

Substance Chemical symbol Minimum ignition energy M-J 

Type of dust Particle size jun Minimum ignition energy mj 

Substance Chemical symbol L/R ratio L ss 0.01 H Minimum ignition energy bJ 

Only in the field of data transmission, communications, remote controlling and monitoring, has the very small energy amount, when switching electric circuits, formed a very useful basis for a special type of explosion protection, the so-called intrinsic safety as given in IEC 60079-11 and EN 50020. 

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Increased safety e (note 1) EN 60079-7 Additional technical measures are implemented in order to prevent with high reliability the possibility of impermissibly high temperatures, sparks and electric arcs inside or outside of an equipment, which do not occur during normal operation. Terminal and junction boxes, control boxes for accommodating Ex devices (which are protected according to a different types of ignition protection), squirrel cage motors, lamps, installation materials, inductive ballasts, transformers... 

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