Reference RN 60079-11 section 5.17

Electrical component or combination of components of simple construction with well-defined electrical parameters which is compatible with the intrinsic safety of the circuit in which it is used.

Items which are simple (usually 2 wire1) with defined characteristics and can be shown to be inherently safe if a (barrier) controlled supply is applied to them are known as simple apparatus and do not require certification but should be assessed for potential static issues.

Such items can, but not exclusively, include:
Switches & Contacts
Switch
Volt-free items e.g. push buttons, magnetic contacts, Mechanical Contacts
Resistors
Resistor examples
RTD's, Light dependent Resistors Potentiometers
Diodes
Diode Examples
Including Zener Diodes and LED's but not LED clusters
Thermocouples
Thermocouple
although they do generate very small voltages
Terminals
including terminal boxes fuses

Items with a low capacitance or inductors can be used but a more extensive asssesment must be made see EN60079-25 Annex H1

No heat dissipating components such as Switches, Terminals etc. can be automatically rated T62

Heat dissipating components e.g. resistors should be assessed.
However, historically it has been accepted to rate them T4 unless there are obvious heating effects.

EN 60079-25 limits the circuit to 1.3w when it contains simple apparatus

Junction box

IS JB
Junction Box
Although such items do not require to be certified it is often specified that an intrinsically safe certified box (assembly) is used.
In most cases this is a result of a misunderstanding of Intrinsic Safety as a system concept and the idea of an enclosure certified intrinsically safe became a marketing ploy pushed by enclosure vendors in the 1990's.
The installation standard3 now calls for evidence of compliance, of the terminal box, to En 60079‑0 when multiple intrinsic safety circuits are inside.

Using a component certified Ex e4 would ensure compliance to EN 60079‑0.
ASSEMBLY CERTIFICATION IS NOT REQUIRED, and therefore the enclosure does not have an external certification plate as it only needs component certification.

Although some vendors push an 'intrinsically safe assembly' with certification plate this can be misleading as the junction box certification plate may be completely different from the intrinsically safe circuits inside. The enclosure would require an identifying labels stating "Contains Intrinsic Safety Circuits" or similar to ensure it is clear this is part of an are intrinsically safe system.

In summary for Terminal/Junction boxes
All terminal boxes must have an intrinsically safe identifying label.
For a single intrinsically safe loop: Enclosure must be physically suitable for environment
For an multiple intrinsically safe loops the Enclosure should have component certification to a relevant protection method e.g. Ex e

Notes

  1. Usually 2 wire but 3 wire devices are allowed if they clearly meet the concept e.g. potentiometers which are can be visualised as to two linked resistors, however 3 wire semiconductors (transistors) would not be simple apparatus. ↩

  2. Non Heat dissipating components can be rated T6 @ 45°C ambient ↩

  3. En 60079-14 'Electrical installations design, selection and erection' ↩

  4. En 60079-7 'Increased Safety' ↩

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