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212 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Motors for Hazardous Duty The IEC classifies hazardous locations into
"zones" according to the probability of a potentially
A summary of the hazardous location designa- explosive atmosphere occurrence. The degree of
tions as outlined in the U.S. National Electrical danger varies from extreme to rare:
Code with a comparison of the international des-
ignation, is outlined in Table 12-8. • Zone 0. An explosive gas-air mixture is con-
IEC standards that address equipment for use in tinuously present or present for long periods
explosive atmospheres are contained in a series of of time. No electric motors may be used in
Publications 79-0 through 79-10. Motor classifica- these areas.
tion and applicability differ considerably from U.S. • Zone 1. An explosive gas-air mixture is likely
standards and practices. Some of these differences to occur in normal operations.
are summarized below. • Zone 2. An explosive gas-air mixture is not
IEC classifies equipment into two broad categories: likely to occur in normal operations, and if
it does occur, will only exist for a short time.
• Group I—Underground mines
• Group II—Use in other industries The following is a comparison of IEC and
U.S. designations:
This discussion is restricted to motors in the
Group II classification, and specifically, to groups IEC Designation U.S. Designation
IIA, IIB, and IIC, which relate to the gas or vapor Group II, Zone 0 rotating equipment gener-
involved. A comparative, but not identical, group- ally not recommended
ing is: Group II, Zone 1 Class I, Division 1
Group II, Zone 2 Class I, Division 2
IEC U.S.
Group II A Group D Construction features and test requirements for
Group II B Group C motors used in hazardous locations are defined by
Group II C Groups A and B the IEC as:

TABLE 12-8. Hazardous (Classified) Location Reference Guide
Specification must include class, division, and group.
CLASS I Areas containing flammable gas or vapor.
CLASS II Areas containing combustible dust.
DIVISION 1 Explosion hazard may exist under International Equivalent
normal operating conditions or due Zone 1
to maintenance, leakage, or
breakdown of equipment.
DIVISION 2 Explosion hazard may exist under International Equivalent
abnormal operating conditions such Zone 2
as rupture of containers or failure
of ventilation equipment.
Class I Group International Equivalent
A Atmospheres containing acetylene IIC
B Atmospheres containing hydrogen and the like IIC
C Atmospheres containing ethylene and the like IIB
D Atmospheres containing acetone, methanol, IIA
propane and the like
Class II Group
E Atmospheres containing combustible metal
Dust such as magnesium or aluminum
F Atmospheres containing combustible
carbonaceous dust such as coal
G Atmospheres containing combustible dust
such as flour, grain, wood, and plastic
For additional information on the properties and group classification of Class I and Class II materials, see Manual for Classification of
Gases, Vapors and Dusts for Electrical Equipment in Hazardous (Classified) Locations, National Fire Protection Association (NFPA) 497M.