IEC 60079-2 — Ex p Pressurisation Standard Explained
IEC 60079-2 covers pressurised enclosures — a protection type used for large control panels, switchboards, and complex electrical equipment that cannot practically be made flameproof or increased safety.
The Pressurisation Principle
Ex p works by maintaining the inside of the enclosure at a pressure slightly above the surrounding atmosphere, preventing any flammable gas from entering. The enclosure is first purged of any flammable gas before energisation, then maintained under positive pressure during operation.
Protection Types
| Type | Description | Zone |
|---|---|---|
| Ex px | Reduces classification inside enclosure to non-hazardous | Zone 1 |
| Ex py | Reduces classification to Zone 2 | Zone 1 |
| Ex pz | Reduces classification to Zone 2 | Zone 2 |
Pre-Purge Requirements
Before energisation, the enclosure must be purged with a minimum of 5 times the internal volume of protective gas (typically clean air or inert gas). This ensures any flammable gas that entered the enclosure during shutdown is fully expelled before live parts are energised.
Ex p systems must have pressure interlocks that automatically de-energise the enclosure if the protective gas pressure falls below the minimum. Door interlocks must also be provided to prevent opening the enclosure while energised in a hazardous area. Failure of either interlock system is a Category X deficiency.
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