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Technical Information and Requirements
Methods of Protection
There are several ways to protect electrical equipment so that arcing or hot components will not be an ignition source causing an explosion.
- Explosion-proof or flameproof protection requires an enclosure that:
- can withstand an internal explosion without rupture, and
- prevents flame or an explosion inside the enclosure from causing an explosion in the surrounding atmosphere outside the enclosure
- Intrinsic safety involves limiting the electrical energy at potential sources of ignition in electrical circuits (hot components and spark sources) to such low levels that-even under abnormal (fault) conditions-there is no possibility of the electrical energy igniting an explosive atmosphere. This method of protection may be used for a wide range of low power equipment, including pagers, process control tank level transmitters, and portable gas detectors.
- Non-incendive equipment also limit energy at potential sources of ignition in electrical circuits (hot components and spark sources). But unlike the intrinsic safety method described above, non-incendive equipment is designed to provide protection only under normal operating conditions, which may include opening, shorting or grounding of field wiring. This method of protection may be used for a wide range of equipment, including pagers, process control tank transmitters, and portable gas detectors.
- Increased safety protection establishes safeguards against the possibility of gas or vapor mixtures being ignited by high temperatures or arcing or sparking under worst-case operating conditions. Increased safety is typically applied to luminaires, motors, and junction boxes.
- Pressurization involves using a protective gas to purge and maintain an internal pressure in the equipment. This prevents an external potentially explosive atmosphere or flammable gas or vapor from leaking into the equipment and contacting otherwise unprotected components. Pressurization is used in equipment such as motors, control panels, and gas chromatographs.
- Encapsulation involves molding the parts that could cause an explosion in a compound to exclude the external atmosphere. It is usually applied to components, such as valve solenoids.
- Dust-tight construction of electrical equipment prevents the entry of combustible or electrically conductive dust in Class II hazardous locations. A bin level indicator would be a typical application.
For the exact definitions, see the Canadian Electrical Code, Parts I and II, available from CSA and the NEC Article 500. To order the Canadian Electrical Code, visit our On-line store.
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