Minimum ignition current

Specifications for intrinsically safe electrical system i General recommendations on the selection of the appropriate group of electrical apparatus based on safe gaps and minimum igniting currents 3682/1991 BS 5501-7/1977 BS 5501-9/1982 BS 5345-1/1989 ... 

Minimum Igniting Current (MIC) Ratio The ratio of the minimum current required from an inductive spark discharge to ignite the most easily igni table mixture of a gas or vapor, divided by the minimum current required from an inductive spark discharge to ignite methane under the same test conditions. 

FPN No. 2) The gas subdivision in (a), (b), and (c) above is based on the maximum experimental safe gap, minimum igniting current, or both. The test apparatus for determining the maximum experimental safe gap is described in lEC Publication 79-lA (1975) and UL Technical Report No. 58 (1993). 

FPN No. 3) The classification of mixtures of gases or vapors according to their maximum experimental safe gaps and minimum igniting currents is described in lEC publication 79-12 (1978). 

Minimum Electrical Spark Gap Minimum Ignition Current... 

Figure 4.2 Electric circuit for the determination of the MIC (minimum ignition current) values of gas-air mixtures.

Figure 6.162 Minimum igniting current I (in A) versus source voltage U (in V) for Groups I, IIA/B/C. Resistive circuits (according to IEC 60079-11 and EN 50020).

If the variety of combustible gases in a chemical plant can be restricted to gases with an increased MIC (minimum ignition current), i.e. if gases classified as IIC can be excluded, then the reference curves, e.g. for Group IIB, may be applied for the same voltage, increased currents are permissible. The difference is a considerable one and is shown as follows ... 

To give an example, Table A.l indicates a minimum ignition current of 3.33 A (safety factor of 1.5 is included) for 12.1 V. Physical effects result in the fact that spark ignition does not occur for voltages below approx. 9-11V. This behaviour may be used to increase power in intrinsically safe circuits to values exceeding 0.5-1 W as available in general. 

Minimum Ignition Energy (MIE) and minimum ignition current as well as... 

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