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What is the difference between Exia, Exib and Exic 

We have an understanding that Exi means Intrinsic Safe protection.

However it is further divided into 3 Types

1) Exia

2) Exib

3) Exic

The key difference between these 3 types is its “fault tolerant capacity”.

The following diagram would help us to understand this concept in a simpler manner

​1.Exia

Picture
Courtesy:Pepperl-fuchs
It has 3 Zener diodes and these are in parallel.

Thus 2 are redundant (i.e if two of them are faulty still the protection is enabled)
​
Thus it is said that in “Exia protection No ignition must be caused in normal operation by one fault or combination of any 2 faults”

2.Exib

Picture
Courtesy:Pepperl-fuchs
It has 2 Zener diodes and these are in parallel.

Thus there is one redundant protection available for this protection concept.
​
Thus it is said that in “Exib protection No ignition must be caused in normal operation by one fault.

3. Exic

Picture
Courtesy:Pepperl-fuchs
It has 1 Zener diode, Thus there is no redundant protection available in this protection concept
​
Thus it is said that in “Exic protection No ignition must be caused in normal operation”.

Where to use Exia, Exib & Exic protection method

Exia is suitable for Zone 0 Area (Thus it is also surely suitable for Zone 1, Zone 2 Area)

Exib is suitable for Zone 1 Area (Thus it is also surely suitable for Zone 2 Area),However it is not recommended be used for Zone 0 Area.

Exic is suitable for Zone 2 Area, However it is not recommended to be used for Zone 0 and Zone 1 Area.

Conclusion

Exia is the most safest option out of these  types of protect and Exic provides the least level of protection as compare to Exia and Exib .

​However it depends on Area/Zone where it is used.As the requirements get stringent the more better protection method is then sought for.
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