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Electric Motors & Hazardous Locations – An Overview

08/11/2020


2020-05-electric motors and hazardous locations sign-1Do you have any hazardous locations at your facility? In all likelihood, you do -- and you need specially rated electric motors & equipment when hazards are present. Here is a summary of what makes a location hazardous followed by an overview of the Class/Division and Zone approaches to classifying those locations.

What Makes a Location Hazardous?

A hazardous location is one where "explosion or fire hazards exist due to the presence of flammable gases, flammable or combustible liquid-produced vapors, combustible dusts, or ignitable fibers or flyings." Hazardous locations are classified based on likely ignitable concentration of combustible materials present at a location.

Depending on the type of hazard present and the risk level involved, there may be certain requirements that AC motors and DC motors have to meet in order to safely function. Also keep in mind that hazardous location requirements can involve both the type of motor that can be installed (e.g., explosion proof Siemens SIMOTICS) and the type of equipment that can be used with them (e.g., AEGIS shaft grounding ring).

NEC Hazardous (Classified) Locations

One of primary systems of classifying hazardous locations is based on NEC article 500 through 503/CEC section 18. It is typically referred to as the Class/Division system and assigns class, division, and material group(s) to hazardous locations

Classes

Classes are based on the type of materials involved and can be further divided into more specific groups.

  • Class I: involves flammable gases and vapors, and can be further divided into groups including the following ...
    • A: Acetylene
    • B: Hydrogen
    • C: Ethylene
    • D: Propane
  • Class II: combustible dusts, further divided into the following groups ...
    • E: Metal dusts (only applies to Division 1 locations)
    • F: Carbonaceous dusts ( dusts that contain 8% or more trapped volatiles such as coal, carbon black, or coke dust)
    • G: Non-conductive dusts (including grain, wood, plastic, starch, flour, etc.)
  • Class III: ignitable fibers and/or flyings

Divisions

There are two divisions and both deal with whether ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors can exist under normal operating conditions. In a Division 1 location, they can exist under normal conditions. In a Division 2 location, they are not likely under normal conditions.

Zones

The Zone system of classifying hazardous locations is based on NEC article 505-506/CEC section 18 can can be summarized as follows:

  • Zones 0 - 2 involve ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors
    • Zone 0: present continuously or for long periods of time under normal operating conditions (i.e., always present)
    • Zone 1: are likely to exist under normal operating conditions (i.e., likely to be present)
    • Zone 2: are not likely to exist under normal operating conditions (i.e., not likely to be present)
  • Zones 20 - 22 involve ignitable concentrations of combustible dust or ignitable fibers/flyings
    • Zone 20: are present continuously or for long periods of time under normal operating conditions (i.e., always present)
    • Zone 21: are likely to exist occasionally under normal operating conditions (i.e., likely to be present)
    • Zone 22: are not likely to occur under normal operating conditions (i.e., not likely to be present)

Electrical Equipment Groups

In addition to zones, electrical equipment (including electric motors and generators) is also divided into groups based on where the equipment will be used.

  • Group I: intended for use in mines susceptible to firedamp (i.e., flammable mixture of gases naturally occurring in a mine).
  • Group II: intended for use in places with an explosive gas atmosphere other than mines susceptible to firedamp and is further divided into subgroups based on what the atmosphere contains
    • Group IIA: propane, or gases and vapors of equivalent hazard
    • Group IIB: ethylene, or gases and vapors of equivalent hazard
    • Group IIC: acetylene or hydrogen, or gases and vapors of equivalent hazard
  • Group III: intended for use in places with an explosive dust atmosphere and is further divided into subgroups based on what the atmosphere contains
    • Group IIIA: combustible flyings
    • Group IIIB: non-conductive dust
    • Group IIIC: conductive dust

Protection Concepts

There are also codes related to the protection methods used to reduce risk. Five of the most common ones are ...

  • Ex d: flame-proof
  • Ex i: intrinsically safe
  • Ex e: increased safety
  • Ex n: in normal operation it is not capable of igniting a surrounding explosive atmosphere
  • Ex t: equipped with an enclosure providing dust ingress protection and a means to limit surface temperatures

Temperature Classifications

Because some flammable materials can be ignited when they come into contact with a hot surface, there are also temperature classifications that apply to both systems of hazardous location classification. They are referred to as the T classes and indicate the maximum surface temperature that the product will not exceed when it operates at a manufacturer-defined ambient temperature.

  • T1: 450ºC
  • T2: 300ºC
  • T3: 200ºC
  • T4: 135ºC
  • T5: 100ºC
  • T6: 85ºC

Interpreting Hazardous Area Codes

Let's look at some examples of how to interpret the codes you will find on equipment rated for use in hazardous locations. Here is an example of Class/Division system codes that are found on approved equipment:

IS CL I Div 1 GP ABCD: rated intrinsically safe (IS) for flammable gases and vapors (Class I) in locations where acetylene (A), hydrogen (B), ethylene (C), and propane (D) can exist under normal conditions (Division 1)

And now for one using the Zone system:

Ex n IIC T5: in normal operation it is not capable of igniting a surrounding explosive atmosphere (Ex n) containing acetylene or hydrogen, or gases and vapors of equivalent hazard (Group IIC) and it has a maximum surface temperature of 100ºC (T5)

Conclusion

It's important to have a good understanding of hazardous locations and how they relate to electric motors. This helps you not only when purchasing new motors but when replacing existing motors, as well. It can also be key when you are looking for a repair shop that works with hazard-rated motors.

 

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Author & Contact Info: Nolan Crowley  (513) 256-9766  ncrowley@hecoinc.com

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