What Is Ex i Intrinsic Safety Protection? A Complete Guide
Ex i intrinsic safety protection is widely used for process instrumentation because the electrical circuits are designed so that they cannot ignite the surrounding explosive atmosphere under the specified conditions.
Ex i, formally known as Intrinsic Safety, is an explosion protection concept used for electrical circuits in explosive atmospheres.
Unlike Ex d Flameproof Protection, which contains an internal explosion, intrinsic safety prevents ignition by controlling the electrical and thermal energy available in the circuit.
The fundamental principle is that the electrical circuits are designed so that, under the specified normal operating and fault conditions, they cannot cause ignition of the surrounding explosive atmosphere.
Intrinsic safety is particularly important for process instrumentation, control, measurement, and communication circuits where electrical energy can be deliberately limited.
Quick Answer
Ex i Intrinsic Safety is a protection concept in which the electrical and thermal energy available in a circuit is controlled so that the circuit cannot ignite the surrounding explosive atmosphere under the specified conditions. The principal levels are Ex ia, Ex ib, and Ex ic.
What Does Ex i Mean?
The designation Ex i comes from the IEC 60079 explosion-protection system.
Ex = explosion protection marking
i = Intrinsic Safety
IEC 60079-11 specifies construction and testing requirements for intrinsically safe apparatus and associated apparatus connected to intrinsically safe circuits entering explosive atmospheres.
The key idea is not simply that the equipment consumes little power. The complete circuit must be evaluated so that its electrical and thermal characteristics remain within the limits required for intrinsic safety.
How Intrinsic Safety Works
Intrinsic safety controls the energy available in an electrical circuit.
Depending on the circuit, relevant parameters can include:
Voltage
Current
Power
Stored capacitance
Stored inductance
Surface temperature
The design must also consider the specified fault conditions applicable to the protection level.
For example, a circuit containing inductive or capacitive components can store energy even when the external power supply is limited. That stored energy therefore has to be considered when demonstrating intrinsic safety.
This is why an Ex i installation cannot be evaluated simply by looking at the nominal power consumption of one instrument.
Ex ia, Ex ib, and Ex ic
Intrinsic safety has different Levels of Protection identified by the suffix following the letter "i".
Ex ia
Ex ia provides the highest level of intrinsic-safety protection among the three Group II levels.
For the applicable fault evaluation, intrinsic safety is maintained with the specified normal operation and two countable faults.
Ex ia is associated with EPL Ga for Group II applications and can therefore be used for applications requiring equipment suitable for Zone 0, subject to the complete certification and installation requirements.
Ex ib
Ex ib provides intrinsic safety with the specified normal operation and one countable fault.
For Group II applications, Ex ib is associated with EPL Gb and can therefore be used for applications requiring equipment suitable for Zone 1, subject to the complete certification and installation requirements.
Ex ic
Ex ic is the lower Group II level of intrinsic safety and is intended for operation under the conditions specified for this level without the additional fault tolerance associated with Ex ia or Ex ib.
For Group II applications, Ex ic is associated with EPL Gc and is intended for applications requiring the Gc level of protection, commonly associated with Zone 2.
Ex i and Equipment Protection Levels
The relationship between intrinsic-safety protection levels and EPL can be summarized as follows:
| Protection | Group II EPL | Typical Zone Compatibility |
|---|---|---|
| Ex ia | Ga | Zone 0, Zone 1, Zone 2 |
| Ex ib | Gb | Zone 1, Zone 2 |
| Ex ic | Gc | Zone 2 |
This table is a selection guide, not a substitute for checking the complete equipment certificate and installation requirements.
The zone does not determine the complete equipment selection by itself. Gas group, temperature class, EPL, certificate conditions, ambient temperature, and installation requirements must also be considered.
Intrinsic Safety Apparatus and Associated Apparatus
An intrinsic safety system normally contains more than just the field instrument.
A typical loop can include:
Intrinsically safe field device
Associated apparatus
Barrier or galvanic isolator
Cable
Control system interface
Associated apparatus is equipment that contains intrinsically safe circuits intended to connect to circuits in the hazardous area. It may be installed outside the hazardous area or may use another type of protection for its enclosure.
The associated apparatus can control or limit the energy entering the intrinsically safe circuit.
Intrinsic Safety Barriers
Two common interface approaches are:
Zener Barriers
A Zener barrier uses components such as Zener diodes, resistors, and fuses to limit voltage and current under fault conditions.
Because the protection relies on a defined earthing arrangement, the installation and grounding requirements must be followed carefully.
Galvanic Isolators
A galvanic isolator provides electrical isolation between the hazardous-area circuit and the safe-area circuit while controlling the energy available to the intrinsically safe circuit.
The specific barrier or isolator must be compatible with the field device and the complete certified system.
What Are Entity Parameters?
Entity parameters are one of the most important concepts when designing an intrinsically safe loop.
Typical field-device parameters include:
- Ui — maximum input voltage
- Ii — maximum input current
- Pi — maximum input power
- Ci — internal capacitance
- Li — internal inductance
Associated apparatus can have corresponding output parameters such as:
- Uo — maximum output voltage
- Io — maximum output current
- Po — maximum output power
- Co — maximum external capacitance
- Lo — maximum external inductance
A simplified compatibility check therefore considers relationships such as:
Uo ≤ Ui
Io ≤ Ii
Po ≤ Pi
and the permitted capacitance and inductance of the complete circuit.
Actual assessment must follow the applicable certification documentation and system requirements rather than relying only on these simplified relationships.
Why Cable Parameters Matter
The cable is part of the intrinsic safety circuit.
Its distributed capacitance and inductance can add to the stored energy of the circuit.
Therefore, the assessment may need to consider:
Cable capacitance
Cable inductance
Cable length
Field-device parameters
Associated-apparatus parameters
This is one reason intrinsic safety is a system-level engineering concept, not simply a property of an individual instrument.
Requirements for intrinsically safe systems are covered by IEC 60079-25, while IEC 60079-11 covers the apparatus requirements for intrinsic safety.
Typical Ex i Equipment
Intrinsic safety is widely used for instrumentation and low-energy electrical circuits.
Examples include:
Pressure transmitters
Temperature transmitters
Flow transmitters
Level transmitters
Intrinsically safe sensors
Process instrumentation
Portable test equipment with appropriate certification
Communication equipment with appropriate intrinsic-safety certification
Typical applications include process measurement, control loops, instrumentation networks, and other circuits where the available electrical energy can be controlled.
Ex i vs Ex d
Ex i and Ex d use fundamentally different protection principles.
| Feature | Ex i | Ex d |
|---|---|---|
| Protection principle | Control electrical and thermal energy | Contain internal explosion and prevent flame transmission |
| Primary standard | IEC 60079-11 | IEC 60079-1 |
| Typical application | Instrumentation and control circuits | Equipment containing ignition sources requiring flameproof containment |
| System considerations | Entity parameters, associated apparatus, cables, and system assessment | Flamepaths, enclosure construction, cable entries, and certified assembly |
| Typical marking | Ex ia / Ex ib / Ex ic | Ex da / Ex db / Ex dc |
Neither protection concept should be selected based only on equipment type. The complete hazardous-area application and certification requirements must be considered.
Understanding an Ex i Marking
A typical marking may appear as:
Ex ia IIC T4 Ga
| Marking | Meaning |
|---|---|
| Ex | Explosion protection marking |
| ia | Intrinsic Safety, protection level "ia" |
| IIC | Gas subgroup |
| T4 | Temperature class |
| Ga | Equipment Protection Level |
The complete marking should be reviewed together with the certificate, entity parameters, ambient-temperature range, special conditions of use, and installation documentation.
See: How to Read IECEx Equipment Markings (Ex db IIC T6 Gb Explained)
Common Ex i Specification Mistakes
Assuming Low Power Automatically Means Intrinsically Safe
Low power consumption alone does not make equipment intrinsically safe. The equipment and circuit must satisfy the applicable intrinsic-safety requirements.
Ignoring Entity Parameters
Field-device and associated-apparatus parameters must be compatible. Voltage, current, power, capacitance, and inductance limits must be evaluated as applicable.
Selecting a Barrier Without Checking the Field Device
A barrier or galvanic isolator cannot be selected independently from the connected field equipment.
The complete loop must be compatible with the relevant certification and entity parameters.
Ignoring Cable Capacitance and Inductance
The cable forms part of the intrinsic-safety circuit. Its electrical characteristics can affect the permitted system configuration.
Confusing Ex ia, Ex ib, and Ex ic
The three levels have different fault-tolerance requirements and associated EPLs. They should not be treated as interchangeable.
Looking Only at the Instrument Certificate
For an intrinsic-safety loop, the complete system arrangement may be relevant. Field device, associated apparatus, cable parameters, installation conditions, and applicable system documentation should all be reviewed.
How to Select Ex i Equipment
A practical selection workflow is:
Determine the hazardous area. Identify the applicable zone and required EPL.
Identify the hazardous substance. Confirm the applicable gas subgroup and temperature requirement.
Select the required intrinsic-safety level. Determine whether Ex ia, Ex ib, or Ex ic is required.
Select the field device. Verify its Ex marking and entity parameters.
Select the associated apparatus. Verify output parameters and certification.
Check entity compatibility. Compare the applicable voltage, current, power, capacitance, and inductance parameters.
Check cable parameters. Include the capacitance and inductance of the installed cable where applicable.
Check ambient temperature. Confirm the certified operating range.
Review special conditions. Check any conditions identified by the certificate.
Verify the complete installation. Follow the applicable system and installation requirements, including IEC 60079-25 where applicable.
Frequently Asked Questions
What is Ex i protection?
Ex i, or Intrinsic Safety, is a protection concept in which electrical and thermal energy in a circuit is controlled so that the circuit cannot ignite the surrounding explosive atmosphere under the specified conditions.
What is the difference between Ex ia, Ex ib, and Ex ic?
They represent different levels of intrinsic-safety protection with different fault-tolerance requirements. For Group II applications, Ex ia is associated with Ga, Ex ib with Gb, and Ex ic with Gc.
Can Ex ia be used in Zone 0?
Ex ia equipment with the appropriate certification and EPL Ga can be used for applications requiring equipment suitable for Zone 0.
Can Ex ib be used in Zone 0?
Ex ib is associated with EPL Gb for Group II applications and therefore does not provide the Ga level normally required for Zone 0 equipment.
Does Ex i always require a barrier?
No. The circuit architecture determines the applicable associated apparatus and protection arrangement. Barriers and galvanic isolators are common, but the complete certified system must be evaluated.
What is an intrinsic safety barrier?
An intrinsic safety barrier is associated apparatus designed to limit the electrical energy available to an intrinsically safe circuit according to its certified characteristics.
What are entity parameters?
Entity parameters are electrical characteristics used to establish compatibility between intrinsically safe apparatus and associated apparatus, including voltage, current, power, capacitance, and inductance parameters.
Can Ex i be used for motors?
Intrinsic safety is primarily applied to circuits where the electrical energy can be controlled within the limits required by the protection concept. Motors and other higher-power equipment generally use other protection concepts depending on their design and application.
What standard covers Ex i?
IEC 60079-11 specifies requirements for equipment protection by intrinsic safety "i." Requirements for intrinsically safe systems are addressed by IEC 60079-25.
What does Ex ia IIC T4 Ga mean?
It identifies intrinsic safety level ia, IIC gas subgroup, T4 temperature class, and Ga Equipment Protection Level. The complete certificate and installation requirements must still be checked.
Conclusion
Ex i Intrinsic Safety protects electrical circuits in explosive atmospheres by controlling the electrical and thermal energy available to the circuit.
Unlike Ex d, which contains an internal explosion, intrinsic safety is based on ensuring that the circuit itself cannot provide sufficient ignition energy under the specified operating and fault conditions.
The principal Group II protection levels are:
- Ex ia → EPL Ga
- Ex ib → EPL Gb
- Ex ic → EPL Gc
For real installations, however, the Ex marking is only part of the evaluation. An intrinsic-safety loop must also be checked for entity parameters, associated apparatus, cable capacitance and inductance, gas group, temperature class, EPL, ambient conditions, certificate requirements, and system installation requirements.
That system-level approach is what distinguishes intrinsic safety from simply selecting a low-power electrical device for a hazardous area.
What Is Ex d Flameproof Protection? A Complete Guide
What Is Ex e Protection? A Complete Guide to Increased Safety
How to Read IECEx Equipment Markings (Ex db IIC T6 Gb Explained)
Gas Groups Explained: IIA vs IIB vs IIC
Temperature Classes Explained: T1 vs T2 vs T3 vs T4 vs T5 vs T6
What Is Equipment Protection Level (EPL)? Ga, Gb, Gc, Da, Db and Dc Explained
Hazardous Area Classification Explained: Zones, Risks, and Equipment Selection
Zone 0 vs Zone 1 vs Zone 2: What's the Difference?
References
- IEC 60079-0 – Explosive Atmospheres – Part 0: Equipment – General Requirements
- IEC 60079-11 – Explosive Atmospheres – Part 11: Equipment Protection by Intrinsic Safety "i"
- IEC 60079-25 – Explosive Atmospheres – Part 25: Intrinsically Safe Electrical Systems
- IECEx System – Certified Equipment Scheme
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