A common hazardous location for fire and explosions, for example, is in agricultural applications. Grain elevators, rice mills, dust pellet mills, flour and feed mills all commonly have combustible dusts in layers or suspended in the air. When oxygen and ignition sources are present, flames can ignite surrounding the ignition source causing an explosion. The best prevention is to eliminate any or all of the factors that when combined create this hazard. One sure way to do that is by eliminating the ignition source when possible.
Sparks or arcs from electrical equipment or wiring
Open flames in welding environments
Chemical reactions or biologial processes
Oxygen levels or elevated temperatures
Compression and shock waves
Apparatus is enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and which operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby. In North America, explosion-proof enclosures are designed to meet the NEC/NFPA and Canadian Electric Code (CEC) requirements, based on a class/division system for hazardous environments.2
Ventilation openings in the motor’s shield and/or frame prevents drops of liquid from falling into the motor within up to 15-degree angle from vertical. Designed for reasonably dry, clean, and well-ventilated (usually indoors) areas. Outdoor installation requires the motor to be protected with a cover that does not restrict the flow of air to the motor.
Dust-tight fan and blower motors for shaft mounted fans or belt driven fans. The motor is mounted within the airflow of the fan.
No ventilation openings, enclosed to prevent free exchange of air (not airtight). No external cooling fan, relies on convection cooling. Suitable where the motor is exposed to dirt or dampness. Not suited in very moist humid or hazardous (explosive) air.
Same as TENV with an external fan as an integral part of the motor. The fan provides cooling by blowing air on the outside of the motor.
Totally enclosed motors are designed for use in extreme conditions - moist and/or chemical environments. Not for hazardous locations.
Same as TEFC with external fan on a power supply independent of the inverter output. Fully cooled even at lower motor speeds.
The motor ambient temperature cannot exceed +40oC. Motors are approved for either Class 1, for use with gases and vapors, or Class 2, to be used with combustible dusts.3
Using Explosion-Proof Motors in Wet and Damp Environments
Rockwell Automation. Class/Division Hazardous Location. Publication 800-WP003A-EN-P - October 2001.
The Cowern Papers