Explosion-proof and spark resistance are two different terms, and there is confusion about them. This article outlines the difference and provides some information on specifying the classification of the application.
Explosion Proof
The term “Explosion Proof” includes the take care of the electrical components like enclosures, motors, controls, and wiring. It is required to enclose any spark from piercing out of the enclosure and igniting the combustible material present in the surrounding environment.
Spark Resistant
“Spark Resistance” is the prevention criteria when the mechanical spares of the hoist lead to a spark in motion. Friction between particular spares can lead to sparks enough to ignite flammable gas or dust. A cigarette lighter is a familiar example of this. The type and dilution of gases in an area are few elements that leverage potential ignition from a mechanically generated source, but other important factors comprise-
- The sorts of materials that make contact
- The speed/pressure that allows the materials to contact
- Corrosion on one or more of the contacting surfaces
- Lubrication
There occurs a spark when steel surfaces contact in non-lubricated conditions. Steel is majorly used in cranes and hoists as load-bearing spares such as lower blocks, load chains, hooks, and trolley wheels, and as such may not be appropriate for some harmful environments.
Application
When an application has to find an Explosion-proof Class, Group, and Condition, the majority of manufacturers and suppliers of cranes and hoists have to know the hazard and the NEC classification explained by the purchaser. The need for spark resistance features also has to be determined by the buyer. As such, we at LOADMATE recommend that buyers extensively research the sources of combustible elements in the operating atmosphere and engage the professional opinion of a technical expert to know the appropriate Explosion Proof Classification and Spark Resistance features.
Explosion-proof and spark resistant features do not come cheap. Depending on the NEC classification, special motors, explosion-proof enclosures, control pendants, and safety limits may be required; sometimes even more than doubling the price of the equipment. The capacity rating of the machine can be reduced when stainless wire rope or chain is needed for spark resistance since it is not equally strong as the same parts in steel. Technology has helped in some classifications using intrinsically safe relays that preclude the need for costly, large, and heavy explosion-proof components. Options to save money on spark resistant features include the use of copper-plated hooks instead of very expensive solid bronze hooks.
The features like explosion-proof and spark resistance are not cheap. Depending on the explosion-proof enclosures, NEC classification, special motors, and safety limits may be needed, a few times making the price of equipment double. The capacity rating of the equipment can be minimized when the stainless wire rope or chain is needed for spark resistance as it is not as strong as the similar parts in steel. Technology has helped in some classifications that use essentially safe relays that prevent the need for costly, heavy explosion-proof spares. Choices to save money on spark resistant features
You can talk to an application expert who can walk you through the needs and ascertain that you get equipment suited to your application.
NEC Explosion Proof Classifications for Machine including Class, Group & Division
Class
- Class I - Locations: In these locations, flammable gases or vapours could be present in the atmosphere in quantities enough to create explosive or ignitable mixtures.
- Class II - Locations: These locations are places in which are perilous as combustible dust is present.
- Class III - Locations: These locations are places that are hazardous easily ignitable fibres, or flyings are present, but where such fibres or flyings are probably not to be in suspension in the air in sufficient quantities to create ignitable mixtures.
Group
- Groups for Class I
- Group A - Atmospheres comprising acetylene.
- Group B - Atmospheres comprising hydrogen, or gases of equal hazards, like manufactured gas.
- Group C - Atmospheres comprising ethyl-ether vapours, cyclopropane or ethylene
- Group D - Atmospheres comprising gasoline, alcohol, hexane, naptha, benzene, butane, benzol, lacquer solvent vapours, acetone, or natural gas.
- Groups for Class II
- Group E - Atmospheres comprising metal dust, including magnesium, aluminium, and their commercial alloys and other metals of equally harmful attributes.
- Group F - Atmospheres comprising coal, carbon black, or coke dust.
- Group G - Atmospheres comprising starch, flour, or grain dust.
Division
- Division I – These are locations or places in which perilous concentrations exist in the air continuously, occasionally, or periodically under normal operating situations.
- Division II – These are locations or places in which hazardous concentrations are handled, processed, or utilized but are generally inside closed containers or systems from which they can escape if there is accidental rupture or breakdown.
When you are buying a hoist or overhead crane, ensure you check all features of the machine, chiefly spark resistance and explosion-proof.
