Testing intrinsic safety of electrical circuits

The standards for intrinsic safety - i EN 50020 and IEC 60079-11, define the scope of type verifications and tests as well as routine verifications and tests (in clauses 10 and 11). Among the type tests  

Due to its construction, there are some limitations for the spark test apparatus  

The spark test apparatus must not influence the circuit to be tested, e.g. the circuit inductance must not be increased by the apparatus inductance. So, the parameters of the apparatus are  

With this spark test apparatus, the reference curves (minimum ignition curves) of Figs 6.162 to 6.167 (showing price ratio ex-protected to non-ex-protected cage induction motors versus rated power types of protection -(E) Ex e IIT3 (E) Ex d IIC T4 and (E) Ex d IIB T4) have been established with reference gas-air mixtures according to Table 6.38. 

In practice, simple circuits may be assessed with respect to the reference curves, i.e. there is no need to apply the spark test apparatus. However, more 

---