NEMA Classifications & Definitions

There are three main categories of classification:

  1. Division
  2. Class
  3. Group

Division: In real sense, it means location or area of the hazard. There are only two types of divisions:

Division 1 Hazard can occur under normal conditions
Division 2 Hazard can occur only under abnormal conditions. Local safety authorities decide what are normal and abnormal conditions. Therefore, the first step is to contact local authorities to define the location if it is Division 1 or Division 2.

Class: Defines the type of hazard. There are three different classes.

Class I Consists of chemical gases or vapors in the environment, such as gasoline or acetylene.
Class II Consists of flammable dust in the environment, such as coke dust, grain dust, etc.
Class III Consists of flammable lint or fibers in the area, such as textile, saw dust, etc.

Groups: Defines the principal chemical gas, vapor or dust present in the environment. The term group comes from the various atmospheric mixtures which have been grouped together on the basis of their hazardous characteristics.

Groups A, B, C, and D are always in the form of gas or vapor. Therefore, these groups can exist only under Class I category.

Groups E, F, and G are always in the form of dust. Therefore, these groups can exist only under Class II category.

Underwriters Laboratories Labeling

Underwriters Laboratories is the only safety agency recognized by the National Electrical Code for the approval of electric motors under hazardous locations. It defines all the requirements for the manufacturers to make these motors after Division, Class, and Groups are defined by the user.

Understanding Where U.L. Label is Required

Special Construction Features

  1. Most are provided with thermal protection. Thermostats, or Thermistors
  2. Most are made of cast iron frames.
  3. Conduit boxes of the motors going in Division 1 are specially sealed.
  4. Class I motors have longer lap joints, tighter fits, and longer flame paths so that if an explosion does occur in the motor, it’s contained in the motor and flames coming out through the joints are cooled enough to be extinguished. They may be bolted by hardened steel bolts.
  5. Motors used in atmosphere of less than -25°C require still stronger construction features because of the extra stresses, also because of the increase in the density of the environment. The amount of energy required to cause an explosion is more, but the explosion is of much greater intensity. Standard explosion-proof motors are not useable below -25oC without special UL testing, approval, and marking.
  6. Class II motors have bearing dust seals.
  7. Non-sparking fan made of aluminum, bronze, or plastic is used to prevent friction sparks in case of any small stones or metal objects getting into the air stream and bouncing off fan blades, and to prevent the build-up of static electrical charge which could generate a spark

View Substances and Atmospheres Chart

Special Information for User:

U.L. does not offer any standards on Division 1 Class 1 Groups A and B.

U.L. does not offer any standards on Division 2 motors.

U.L. does not offer any standards on Class III motors.

U. L. does not offer any standards for motors used below ambient temperatures of -25°C, but will conduct individual tests at whatever low ambient is desired.

Motors rated ¾ HP and less may have internally mounted automatic thermal overload. Caution should be observed when applying these to the machinery as automatic thermal overload resets and starts the motor.

Motors rated 1 HP and more may have thermostats on the windings which are pilot circuit devices only to be connected into the magnetic starter circuit.

Open motors can only be used in Division 2 location.

Operating temperature of space heaters must be considered when non-UL listed motors are applied in Division 2 locations. Any heater temperature below 200°C.

Conclusion

This page provides the general everyday information. The user should be very careful about the special situations which are not covered by National Electrical Code tables. The main limiting factor is the surface temperature of the motor which should always be below the minimum ignition temperature of the environment. It should also be strong enough to contain any explosion inside.

Recognized UL Component Mark for Canada and the US


This new UL Recognized Component Mark, which became effective April 1, 1998, may be used on components certified by UL to both Canadian and U.S. requirements. Although UL had not originally planned to introduce a combined Recognized Component Mark, the popularity of the Canada/U.S. Listing and Classification Marks among clients with UL certifications for both Canada and the United States has led to the new Mark.

Special Information for User

The latest revisions of the U.L. Standards are primarily additional safety features and in no way affect the safe operation of U.L. labeled motors now in use. The most significant change in the revised Standards is that all motors must bear a marking indicating maximum operating temperature. This change, in effect, further subdivides each of the exisiting U. L. groups.

Special Information for User The latest revisions of the U.L. Standards are primarily additional safety features and in no way affect the safe operation of U.L. labeled motors now in use. The most significant change in the revised Standards is that all motors must bear a marking indicating maximum operating temperature. This change, in effect, further subdivides each of the exisiting U. L. groups. The marking to show maximum surface operating temperature must be in either degrees C or F, or by code, indicating the temperature range, i.e., a motor having a maximum surface operating temperature of 165oC may be marked 165oC or 329oF or coded T3B. All temperatures are on the highest temperature obtained in an ambient of 40oC (104oF) under all operating conditions, including overload, single-phasing, and locked-rotor operation. National Electrical Code (2002) Article 500-8(B) lists the preferred markings in part in chart linked below.

View Preferred Markings in Part Chart

Canadian Standards Association – CSA

Most motors sold and used in Canada require C.S.A. certification. This involves submitting design details and testing of motors. Below is a tabulation of motors which are presently certified to C.S.A. standards. Auxiliary devices such as bearing RTD’s and vibration switches are not included, and are to be submitted to C.S.A. for investigation and acceptance before they can be used on the motor.

Special Markings: Motors are to be marked on the nameplate with the C.S.A. symbol, and code-dated with month and year of manufacture (e.g. “1281” means December1981). Any warning labels must be bilingual (English-French). All motors to have C.S.A. accepted ground terminal mounted inside the conduit box.

Special Marking


C.S.A symbol on motor main nameplate and on UL label. Date code for year and month of manufacture (e.g. “1281” means December 1981). Any warning labels must be bilingual (English-French). All motors to have C.S.A. accepted ground terminal mounted inside the conduit box. Requirements for motors not included in the above two tables should be discussed with the factory. Where good business opportunities exist, special C.S.A. acceptance on a case basis can normally be obtained within a few months after the application is submitted to C.S.A. The investigation usually requires C.S.A. inspection of the motor, test data, and, sometimes, C.S.A. testing of motor components.

Motor

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