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# Intrinsically safe calculation.

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## Intrinsically safe calculation.

(OP)
Hello,
I have a question regarding intrinsically safe calculations to iec 60079. For example from instrumentation tools.com
Evaluating conditions for Intrinsically safe Loop:

Vmax must be greater than or equal to Voc
Imax must be greater than or equal to Isc
Ci + Ccable must be less than or equal to Ca
Li + Lcable must be less than or equal to La

Entity parameters of Intrinsically safe apparatus (INSTRUMENT)

Vmax(Ui): Maximum voltage that may be applied safely to the intrinsic safe apparatus

Imax(Ii): Maximum current that may be applied safely to the intrinsic safe apparatus

Ci: Internal capacitance of intrinsic safe apparatus

Li: Internal inductance of intrinsic safe apparatus

Entity parameters of Associated apparatus (SAFETY BARRIER)

Voc (Uo): Maximum open circuit voltage that can appear across the intrinsically safe connections of the associated apparatus under fault condition

Isc (Io): Maximum short circuit current that can be drawn from the intrinsically safe connections of the associated apparatus under fault condition

Ca: Maximum capacitance that can be connected safely to the associated apparatus

La: Maximum inductance that can be connected safely to the associated apparatus

(AboveFrom instrumentation tools)

My question is do all cables between the instrument and control system need to be considered to satisfy the capacitance and induction conditions above. So for example if we have a flow meter would we need to consider
the cable between the instrument(meter) and the remote transmitter.

The cable between the transmitter and local junction box and

The cable between the local junction box and control system

Thank you

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