Intrinsic Safety Concept

Intrinsic Safe is a low energy signalling technique that prevents explosions from occurring by ensuring that the energy (I.e. voltage, current and power is restricted) transferred to a hazardous area is well below the energy required to initiate an explosion. The energy levels made available for signalling are small but useable and more than adequate for the majority instrumentation systems.

Capacitance and inductance properties of cables have the energy storing capabilities, they can affect system safety. In general the max. Voltage available is set by capacitance and max. Current by cable inductance.

For example 400 meter cable capacitance corresponds to 80nF and inductance is 400µH which has a permissible voltage of 29V and current of 300 mA in IIC ia circuit as per ignition limit curve, which easily permits a T4 (i.e. 135 °C) temperature classification.

Please refer IEC 60079-11 or EN 50020 for more details about the ignition limit curve for permissible max. voltage and current limit for hazardous area ia,ib,ic.

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