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204 SHALE SHAKERS AND DRILLING FLUID SYSTEMS
seal where the shaft exits the motor shell. Relu- ence of these standards, each country had its own
brication is necessary to replenish grease that national certifying authority. Today, with certifica-
has broken down by oxidation, or lost by evapo- tion from recognized "national testing houses," the
ration, and by centrifugal force. Double-shielded motors are acceptable in all EEC countries and
and sealed bearings, however, cannot be lubri- most other European and Asian countries as well.
cated after manufacture. Electric equipment certified to conform to these
Inspect and keep cooling and ventilation vents standards may be installed and used in any EEC
clear of obstructions. member state. Participating non-EEC states may
If a motor burns out, the windings should be in- require additional testing standards.
spected for signs of single-phasing, short-circuiting,
overloading, and voltage unbalance. Any cause of
winding damage should be identified and corrected. Comparison of U.S.
If a motor burns out, the circuit supplying the volt- and IEC Nomenclature
age should also be inspected for broken or shorted
wires, burnt contacts, or voltage imbalance. While there are many similarities and even direct
interchangeabilities between U.S. and IEC recognized
standards, specific applications must be considered.
ELECTRIC MOTOR STANDARDS Motors may be acceptable under all standards but
not necessarily certified under all standards.
Generally, standards for electric motors are based The IEC "flame-proof" motor is essentially the
on the International Electrotechnical Commission same as the U.S. "explosion-proof" motor. Each
(IEC), the National Electrical Manufacturer's Associa- design withstands an internal explosion of a
tion (NEMA), and the Institute of Electrical and Elec- (specified) gas or vapor and prevents ignition of
tronic Engineers (IEEE). Most countries typically have the specified gas or vapor that may surround the
their own standard or a recognized standard. motor. However, construction standards are not
identical. The U.S. standard is generally more
stringent and acceptability can be based on ap-
U.S. Standards proval of local authorities.
The U.S. totally enclosed "purged and pressur-
NEMA designs (A, B, C, D, and E) classify motors ized," or "inert gas filled," motors are manufac-
according to specific torque characteristics for tured to similar standards as those of IEC pressur-
effective startup and operation of equipment under ized motors. Each operates by first purging the
particular loading and operating situations. Design motor enclosure of any flammable vapor and then
B motors are commonly used on drilling rigs. preventing entry of the surrounding (potentially ex-
These are general purpose motors suitable for plosive or corrosive) atmosphere into the motor
normal startup required by pumps, fans, and low- enclosure by maintaining a positive gas pressure
pressure compressors (Figure 12-2).
within the enclosure.
IEC Type 'e' (Increased Safety) motors are non-
European Standards sparking motors with additional features that provide
further protection against the possibilities of excess
In Europe and Asia national standards for elec- temperature and/or occurrence of arcs or sparks.
tric motors are, in general, based on the Interna- NEMA and IEEE standards and testing are more
tional Electrotechnical Commission (IEC). The IEC comprehensive than the IEC standards. In general,
facilitates coordination and unification of motor motors designed to NEMA/IEEE standards should
standards. IEC standards for dimensions, toler- be suitable for application under IEC standards
ances, and output ratings are contained in IEC from a rating, performance, and testing viewpoint.
Publications 72 and 72A. IEC standards for rating, Mounting dimensions and tolerances should always
performance characteristics, and testing of rotat- be verified.
ing machinery for nonhazardous locations are
contained in a series of IEC Publications No. 34,
while IEC standards dealing with apparatus for ENCLOSURE AND FRAME
explosive gas atmospheres are contained in a DESIGNATIONS
series of Publications No. 79.
The IEC recommendations hold international Motor Enclosures
applicability. The European standards are identi-
cal in all countries in regard to their contents and Motors operate best in areas free of airborne
are published as national standards. Before exist- particles and corrosives and should have sufficient
