Intrinsically Safe circuits achieve safety by maintaining very low energy levels so that hot surfaces will not be produced, and any electrical sparks will not have sufficient energy to ignite the most easily ignitable concentration of a flammable mixture.
This is achieved by limiting the voltage and current supplied to the equipment in the hazardous area. These levels of voltage and current must not be exceeded under normal or fault conditions.
The circuit parameters, voltage, current, resistance, inductance and capacitance are factors considered during the design of IS circuit.
The standards give the required data in tables, and in graphical form (the characteristic ignition curves), for Group 1 and Group II subdivision IIA, IIB & IIC gases.
