Exp Enclosures | Purge & Pressurization Enclosures | ATEX Zone 1 & Zone 2 (21/22) Hazardous Areas
Exp enclosures (Purge and Pressurized ) enable the user to install uncertified electrical equipment in hazardous areas.
Expo Purging & Pressurization Systems from Thorne & Derrick International have UL Listing for US hazardous locations and cUL listing for Canadian Zones.
Exp enclosures can also be certified to ATEX or IECEx standards.
Please Note: If a purging system is provided which attaches to your enclosure, a notified body must certify it.
Type of Explosion Protection ‘p’ – Pressurization
Ex p pressurized equipment is the technique of guarding against ingress of the external atmosphere into an enclosure by maintaining a protective gas therein at a pressure above that of the external atmosphere.
The Principle of a Pressurized Apparatus
The entry of a surrounding atmosphere into the enclosure of the electrical apparatus is prevented by maintaining a protective gas, inside the enclosure, at a higher pressure than the surrounding atmosphere. The overpressure is maintained either with or without a continuous flow of the protective gas.
- Product Range Overview
- Exp Enclosures | Pressurized Enclosures | Ex px Class I Div 1 | Zone 1 & 21 ATEX Hazardous Areas
- Exp Enclosures | Pressurized Enclosures Ex pz Class I Div 2 Zone 2 Zone 22 ATEX Hazardous Areas
- Dust Protected Enclosures Ex tb Ex tc Class II Zone 21 Zone 22 ATEX Hazardous Areas
- Increased Safety Enclosures Ex e Ex tc Class II Zone 2 Zone 22 ATEX Hazardous Areas
- Restricted Breathing Enclosure EEx nR Class II Zone 2 ATEX Hazardous Areas
Ex p Current Standards
- IEC 60079-2 (EN 60079-2) Explosive atmospheres – Part 2: Equipment protection by pressurized enclosures ‘p’
- IEC 60079-13 Equipment protection by pressurized room ‘p’
- IEC 600-79-16 Electrical Apparatus for Explosive Gas Atmospheres Part 16: Artificial Ventailation for the Protection Analyser (s) Houses.
EPL/Category and Zones of Use
Protection by pressurization is subdivided into three protection types (px, py and pz).
This equipment may have the alternative markings of pxb, pyb and pzc. Equipment is selected based upon the external explosive atmosphere, the potential for an internal release whether the equipment within the pressurized enclosure is ignition-capable.
Pressurization – Type of Explosion Protection
The following table explains Pressurization type of explosion protection:
|Location EPL||Enclosure contains ignition-capable equipment||Enclosure does contain ignition-cable equipment|
|‘Gb’||Type ‘pxb’||Type ‘pyb’|
|‘Gc’||Type ‘pxb’ or ‘pzc’||No pressurization required|
Notes: IEC 60079-2 requires the type ‘py’ equipment will only contain equipment to type of protection ‘d’, ‘e’, ‘i’, ‘m’, ‘nA’, ‘nC’, ‘o’ or ‘q’
Benefits of Exp Purge & PRESSURIZED Enclosures
Quick Access: Easily open purged cabinets for maintenance in hazardous areas;
- Hazardous Area Zone 1 or Class I Div 1: When the door opens and the internal air-pressure falls, power automatically switches off. When the door closes, after the required number of purge cycles the enclosure automatically powers-up.
- Hazardous Area Zone 2 or Class I Div 2: When the door opens, a low-pressure alarm sounds. However, the equipment operates for a time you set, based on local risks.
- Windows: for viewing displays;
- HMI units either directly, if they support pressurization, or into inset housings, if separately approved;
- Operator interfaces: push buttons, lamps, switches, and annunciators. We must use certified components since they sit outside the enclosure.
Heating & Cooling: Exp enclosures often include local heating or cooling:
- Electric heating;
- Fan-driven heat exchangers;
- Vortex coolers.
Wheels: Move certified electrical equipment between points of use in hazardous areas.
- Multiple hazardous areas can share a single piece of equipment;
- E.g. filter cleaning systems in pharmaceutical plants.
Why use Exp Purge & pressurized enclosures?
Exp enclosures are cost effective as a single unit often purges multiple enclosures in a series and is able to replace multiple explosion-proof boxes and interlinking conduit. The purge and pressurized enclosures are easy to reconfigure or upgrade when required.
Expensive alternatives to purge and pressurized enclosures include:-
Explosion-Proof Junction Boxes (Ex d): Exd enclosures can withstand an internal explosion, and prevent any internal ignition reaching surrounding gas or vapour. However, these are heavy, solid metal boxes, generally castings, or specially welded/fabricated. Hence:
- Access, e.g. for maintenance, is time-consuming because multiple bolts or thread engagements secure the lid;
- Design changes are expensive, because any modification, e.g. local drilling, is forbidden;
- Extracting internally generated heat is expensive and difficult;
- Large boxes are disproportionately expensive;
- Boxes are approved for specific internal equipment layouts.
Increased Safety Enclosures (Ex e): for equipment that doesn’t arc or spark during normal or fault conditions. The enclosure is insulated to keep surface temperatures below incendive temperatures. However:
- Only Ex e approved components can be installed inside the enclosure;
- No sparking or arcing equipment is permitted;
- The enclosure’s certificate sets specific conditions & limits.