Encapsulation works by enclosing equipment in a special potting compound in order to keep the potentially explosive atmosphere away from the source of ignition. There are however, several drawbacks with this type of protection.
- The testing part of the certification process takes at least five weeks and the outcome is by no means certain.
- The encapsulated product is subjected to high temperature conditioning for four weeks and, with the differences of thermal expansion of internal parts, can lead to cracking and splitting of the encapsulant.
- Accessibility and serviceability of the product is sacrificed, since the potting should cover all parts of the circuit.
On the plus side however there is not much restriction to the design of the circuit, although some modification may be needed because a single fault has to be applied to the circuit without damaging the potting.
Thermal fuses can provide this protection either built in or as a ‘piggy back’ board.
Important Design Parameters
- Breakdown strength
- Low water absorption
- Resistance to various influences
- Potting must be of stipulated thickness all round
- Cavities are only permitted to a limited extent
- Potting is only penetrated by cable entries
- Load on components is limited or reduced.
- Increased clearance between live parts.
Static coils in ballast, solenoid valves or motors, relays and other control gear of limited power, and complete PCBs with electronic circuits.