Jim Bryan (deceased)
Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO
Hazardous location motors, often referred to as explosion-proof motors, are designed and tested for use in environments where fire or explosive hazards may exist due to flammable gases, vapors, combustible dusts, or ignitable fibers. These motors must contain any flame within the motor to prevent ignition of the surrounding atmosphere. Various standards govern the use of these motors, including those from Underwriter’s Laboratories (UL), Canadian Standards Association (CSA), International Electrotechnical Commission (IECEx), Mine Safety and Health Administration (MSHA), Factory Mutual (FM), Atmosphères Explosibles (ATEX), and British Approvals Service for Electrical Equipment in Flammable Atmospheres (Baseefa).
Once a motor design is tested by a third-party laboratory, a label can be affixed designating the hazardous locations in which the motor can be safely operated. This label must be present when the motor is in operation. The paper primarily discusses UL standards, with some correlation to IECEx standards. It is crucial to be familiar with the standard governing your jurisdiction.
To repair motors used in hazardous locations, the repairer must be certified by the certifying agency, such as UL. This certification involves documenting any work that disturbs the flame path and notifying UL, often through routine inspections. The flame path is an opening with a small clearance and sufficient length to contain the flame within the motor. Certification requires a visit to the UL website, where information on the application process, costs, and requirements for shop capabilities and documentation can be found.
UL maintains a file for each motor design tested, with specifications derived from UL 674. There are separate specifications for manufacturing and repair. If repairs are not performed per the specification, the UL label must be removed, and the motor can no longer be used in a hazardous location. Under certain circumstances, such as manufacturer warranty repairs, the manufacturer can authorize the use of their file for repair purposes.
Hazardous locations are classified by UL using a system of classes, groups, and divisions, while IECEx uses zones and groups. Motors can only be restored to the class and group for which they were originally approved. The paper provides definitions for these classifications, including Class I for flammable gases and vapors, and Class II and III for explosive dust atmospheres and ignitable fibers. The auto-ignition temperature of materials in these environments determines the surface temperature limit for the motor.
Safety in hazardous environments is critical, and adherence to regulations from certifying agencies is essential to prevent loss of life and property. If repairs are done in a non-certified facility, the label must be removed, and the motor should not be installed in a hazardous environment.
Key Points Covered:
- Definition and importance of hazardous location motors
- Standards governing hazardous location motors (UL, CSA, IECEx, etc.)
- Certification process for repairers
- Importance of flame paths and documentation during repairs
- Classification systems for hazardous locations (UL and IECEx)
- Auto-ignition temperature and surface temperature limits for motors
- Safety and adherence to regulations
Key Takeaways:
- Hazardous location motors must contain any flame within the motor to prevent ignition of the surrounding atmosphere.
- Repairers must be certified by the relevant certifying agency to perform repairs on these motors.
- The certification process involves documenting work and routine inspections by the certifying agency.
- Motors can only be restored to the class and group for which they were originally approved.
- Adherence to regulations is essential to ensure safety in hazardous environments.
- If repairs are done in a non-certified facility, the label must be removed, and the motor should not be installed in a hazardous environment.
