FAQ - FNICO
| Q |
How does FNICO differ from conventional non-incendive practice |
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| A | Conventional Non-incendive practice does require cable parameters to be calculated, and the voltage and current values of apparatus to be matched. In the case of North American approvals, the V, I , C and L values are stated in the 'non-incendive field wiring parameters', which are part of the approvals listing. The same principle exists for energy-limited approvals for EN 50021, which carry the approvals code EEx n L. This is just like Intrinsic Safety, but note that some North-Amarican NI approvals do not allow live working on the wiring at all, in which case no non-incendive parameters are published. FNICO is like FISCO in that it eliminates the need to calculate cable parameters, provided the cable complies with a minimum requirement (which is the same as that for FISCO). As far as matching power supplies to field instruments is concerned, FNICO requires only that the voltage values are compatible, and in this case the Vmax for the field device can be taken either from its NI approvals or (if no NI approval is stated) from the Intrinsic Safety approvals. The overall result is that FNICO systems are as easy to design as FISCO, but with the benefit of more field devices per trunk due to the relaxed factor of safety for Division 2 apparatus. |
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| Q |
To what extent can we trust the stated FNICO parameters |
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| A | FNICO stays within the boundaries of the experimental work done by PTB for FISCO, so additional testing is not required to prove the safety of FNICO systems. The figures proposed for the MTL FNICO power supplies have been further confirmed by BASEEFA when testing the FISCO units. The FNICO model removes the 1.5 safety factor on current required by the IS standard, and replaces this with the 1.1 factor required by the North American standards, but apart from this no other parameters (including cable parameters) have been modified. MTL is in the process of writing appropriate apparatus and systems standards, together with a code of practice. Longer term, these documents are the basis for a more formal standard and endorsement by the appropriate approvals bodies. |
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| Q |
What is the status of the FNICO standard? |
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| A | The FNICO Technical Specification, in the form of a draft document, has been circulated for comment to PTB in Germany, Baseefa2001 in the UK and Factory Mutual in the US. The initial reaction has been positive in that no technical objections have been raised. FNICO, and the application of FISCO principles to fieldbus applications in Zone 2, were discussed at the IEC SC 31G Intrinsic Safety committee meeting in Dubrovnik, 7-11 April 2003. At the same meeting, it was provisionally agreed that the energy-limited protection technique (Ex nL) for Zone 2 will be transferred from the existing Ex n committee into the intrinsic safety committee. This will give the non-incendive technique, and FNICO itself, a stronger position than at present, with the possible eventual adoption as 'Ex ic'. If this goes ahead, then it looks probable that FNICO will gain IEC recognition by being adopted into the FISCO standard. | |||