Encapsulation in Intrinsically Safe Circuits

07 Aug 2026

A Closer Look at IEC 60079-11:2023 Ed 7

In intrinsic safety, encapsulation is a protection method where an electrical circuit, component, or part of a circuit is covered or enclosed by a solid insulating compound. According to IEC 60079-0, the compound used for encapsulation may be a thermosetting, thermoplastic, epoxy resin, elastomeric material, or similar material, with or without fillers and/or additives, in their solid state.

Encapsulation plays an important role in intrinsic safety evaluations because it can reduce or limit the parts of the circuit that need to be considered for spark ignition risks. In addition to excluding the explosive atmosphere from the encapsulated parts. To achieve this, the minimum thickness to the free surface of the encapsulating compound encapsulation shall be at least 1mm. Encapsulation can also improve the thermal behavior of components that are relied upon to achieve the intrinsic safety rating. When a component is encapsulated, the heat is not dissipated only through the component leads and surrounding free air. The encapsulating compound can provide an additional thermal path around the component. This can reduce the temperature rise of the component compared with the same component operating in free air, depending on the thermal properties of the compound.

A typical example is a Zener diode used as a safety component in an intrinsically safe circuit. When tested in free air, the Zener rating is based mainly on its normal heat dissipation path. However, when the Zener is encapsulated in a suitable compound, the encapsulation can improve on transferring heat away from the diode which may thus support a higher assessed power rating.  

However, thermal evaluation of the compound is also an important consideration when encapsulation is used. The Continuous Operating Temperature (COT) range of the encapsulating compound must be suitable for the rated ambient range of the product and for the temperatures reached at the interface between the compound and the encapsulated components during normal and fault operation. The evaluation should confirm that the surface temperature of encapsulated components does not exceed its maximum COT. Operation above the compound’s COT is only acceptable where it has been demonstrated, by inspection or assessment after the applicable test conditions, that the encapsulation has not been damaged in a way that could affect intrinsic safety. This includes confirming that the compound does not crack, shrink, swell, soften, decompose, or expose encapsulated parts.

The free surface of the compound must have a suitable Comparative Tracking Index (CTI), where bare conductive parts protrude from the compound. CTI is related to the material’s ability to resist electrical tracking across its surface. Requirements based on the voltage can be found in Tables 7, 8, and 9 of IEC 60079-11:2023 Ed 7. This is mainly important when the compound surface is part of the insulation system between conductive parts.

The encapsulating compound may be used as part of the enclosure when its exposed surface is relied upon to maintain the intrinsic safety protection. In this case, the compound is not only filling or covering the circuit, it is also acting as an external protective surface. Therefore, the compound must pass the mechanical tests of IEC 60079-11:2023 Ed 7 Clause 9.4.1 to confirm that it can withstand an impact without damage, permanent deformation, or movement greater than 1mm. The compound must be applied in a way that maintains proper adhesion and sealing where needed. The encapsulation process should also include documented controls to prevent voids or defects that could affect the intrinsic safety protection.

Free space within the encapsulation must be evaluated when encapsulation is used for the exclusion of explosive atmospheres. Free space within components such as transistors, relays, fuses does not need to be considered when the component volume is less than 1 cm³. The evaluation should consider the size of each individual free space, the total free space within the encapsulated volume, the required compound thickness around the free space, and protection against access. For Group I and Group II, the permitted free space depends on the level of protection, with “ia” being more restrictive than “ib” and “ic” must comply with Table 11. For Group III, the total free space is not limited but individual free spaces must comply with Table 12.

Encapsulation can also have a positive effect on the spacing assessment in intrinsic safety evaluation. When conductive parts, PCB tracks, component leads, or PCB layers are properly encapsulated, the required minimum separation distances may be reduced compared with parts separated only by air. This is because the casting compound provides a solid insulating barrier between conductive parts and helps exclude the explosive atmosphere from the encapsulated area.

In accordance with IEC 60079-11:2023 Ed 7, Table 7, the standard provides different spacing requirements depending on the type of separation and voltage. For example, for Level of Protection “ia” and “ib” at 10V, the required clearance through air is 1.5 mm, while the required separation distance through casting compound is reduced to 0.5 mm. This shows that encapsulation can allow a more compact PCB design while still maintaining the required intrinsic safety separation distances.

Encapsulation is an effective and important technique in intrinsically safe circuit design when it is properly applied and evaluated in accordance with IEC 60079-11:2023 Ed 7. It can be used to exclude explosive atmospheres from electrical parts, reduce the need for spark ignition assessment, provide mechanical protection, support reduced separation distances, protect critical components, and improve the thermal behavior of components relied upon for intrinsic safety. The use of encapsulation provides clear design advantages, especially for compact or complex circuits.