Divisions and Classes on Motors – What Do They Mean?

One of the largest safety concerns in an industrial plant is the occurrence of a fire or explosion. If potentially dangerous gases or vapors are present in your application, you need an explosion-proof motor. It can be a seemingly challenging task to select the proper motor, but we’re here to help! Thankfully there are divisions, classes and groups that help to narrow down your selection.

It’s not as easy as saying, “I want an explosion-proof motor”. Totally Enclosed Fan Cooled (TEFC) and Open Drip Proof (ODP) motors are general purpose motors that don’t carry any ratings. It’s a common misconception that these motor enclosures have explosion-proof ratings. However, that’s not the case. You need to specify which ratings are required for your application and install a proper motor.

Divisions

The first step in choosing an explosion-proof motor is to define its division. The motor’s division classifies how often the potentially explosive materials are present during normal operating conditions. There are only two divisions for motors in hazardous areas.

Division 1: Ignitable concentrations are present all or most of the time. This includes during frequent maintenance, equipment failure or repair work.

Division 2: Ignitable concentrations are not likely to be present during normal operation. The hazardous materials might be handled or processed, but are normally in closed containers or closed systems that could only be exposed during an accident or failure of that container or system.

For example, let’s think about a gas station. The underground tanks and gas pumps themselves are classified under division 1 because they are directly handling the potentially-explosive materials. The rest of the near-by gas station components should be classified under division 2 because they might be exposed to the potentially-explosive materials at any time.

Classes and Groups

Next, you need to determine the hazard class of the potentially explosive materials you’re dealing with. These hazards are separated into three different classes. You must select a motor that is properly classified for your specific application.

Class 1: Locations with flammable gases, vapor and liquids

Class 2: Locations with combustible dusts

Class 3: Locations with ignitable fibers and flyings

The Class 3 motor is the least common and isn’t divided any further into groups. However, Class 1 and 2 motors are grouped by your specific hazardous substance. The most common groups and materials are listed below.

Group A: Acetylene

Group B: Hydrogen, Butadiene, Ethylene Oxide, Propylene Oxide, Acrolien

Group C: Ethylene, Cyclopropane, Ethyl Ether

Group D: Propane, Acetone, Ammonia, Benzene, Butane, Ethanol, Gasoline, Hexane, Methanol, Methane, Naptha, Natural Gas, Toluene

Group E: Combustible Metal Dusts (Aluminum, Magnesium Commercial Alloys)

Group F: Combustible Carbonaceous Dusts (Coal, Carbon Black, Charcoal, Coke Dusts)

Group G: Other Combustible Dusts (Flour, Grain, Wood, Plastic, Chemicals)

Temperature Class (T Code)

The “T” Code identifies the maximum absolute motor surface temperature that will be developed under any operating condition. This is not a value that you will choose, but instead the result based on the division, class and group. This is important to note because the motor you end up with should have a maximum surface temperature that is below the ignition temperature of the potentially explosive material in the hazardous area.

Once you’ve determined the division, class and group of your motor, you’re ready! Use those ratings/values to select the proper motor for your hazardous application. Be sure to involve the safety members at your facility so they can give input as to what ratings are required. If you’re in Upper Michigan or Wisconsin, we can get you the right motor… just contact us!