Page 224 - Shale Shakers Drilling Fluid Systems

206 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

cool airflow to dissipate heat developed during IEC 112M28 = 112 mm foot height, M frame length,
operation. Poor ventilation causes many industrial 28 mm shaft diameter
motor failures. Motors should also be protected or IEC 18M1-1/8 = 4.5 foot height, M frame length,
shielded from damage by liquids. Rarely, if ever, 1 ^--inch shaft diameter
do all these conditions exist. NEMA has defined o
various enclosures suitable for different operating In IEC nomenclature, when a flange exists on
environments (Table 12-2). the drive end, the flange number is added directly
following the shaft diameter. For example:
NEMA and IEC Frame Dimensions
112M28F215 =112 mm foot height, M frame length,
IEC Publications 72 and 72A provide standards 28 mm shaft diameter, 215 mm pitch circle di-
for dimensions, tolerances, and output ratings. ameter flange
Publication 72A, an extension of Publication 72,
addresses larger machines. There are small, but
significant, differences between the IEC and NEMA Protection Classes Relating
frame dimensions (Table 12-3). In most cases, to Enclosures
machines built to either series can be adapted by
special machining or shimming. For example, the The ingress protection code (IP), published as
IEC bolt hole is larger than the NEMA bolt hole. European Standard EN 60 529, provides for enclo-
Couplings can normally be obtained or machined sures that:
that accommodate the shafts of either series.
One potential point of confusion between NEMA • Protect against contact with live or moving
and IEC dimensional nomenclature is the different parts
letter symbols used to indicate basic mounting • Protect against entry of solid foreign matter
dimensions (Table 12-4). For example: • Protect against water entry

TABLE 12-2. Widely Used Electric-motor Enclosures

Open motors (IEC class IP 00) have ventilating openings for passage of external air over and around the windings
for cooling purposes.
Drip-proof motors (IEC class IP 12) are open motors protected from entry of liquids or solids falling on the motor at
angles up to 15° from vertical.
Guarded motors (IEC class IP 22) are open motors with ventilating openings of such size and shape to prevent
fingers or rods from coming in contact with rotating or electrical parts.
Splash-proof motors (IEC class IP 46) are open motors protected from entry of liquids or solids falling on the motor
or coming in contact with the motor in a straight-line path at angles up to 100° from vertical.
Totally Enclosed motors (IEC class IP 44) are constructed to prevent free exchange of air between the inside and
outside of the motor case but are not airtight.
Totally Enclosed Nonventilated (TENV) motors are totally enclosed but not self-equipped for cooling.
Totally Enclosed Fan-Cooled (TEFC) motors are totally enclosed with a shaft-mounted fan that directs air across
the external frame (applications include dusty, dirty, corrosive atmospheres).
Totally Enclosed Blower-Cooled (TEBC) motors are totally enclosed motors with an independently powered
external frame cooling fan.
Encapsulated motors have coated windings to protect them from moisture, dirt, and abrasion.
Dust-Ignition-Proof motors are totally enclosed motors designed to exclude the entry of combustible dusts into the
enclosure or bearing chamber. They are also designed to operate under any normal or abnormal operating condition
(including heavily blanketed with dust) such that external surface temperatures of the motor casing do not exceed
the motor's maximum operating temperature.
Explosion-proof motors (IEC "flame-proof") are totally enclosed motors built to contain the flames and pressures
resulting from repeated internal (inside the motor casing) explosions. They are also designed to operate under any
normal or abnormal condition such that external surface temperatures of the motor casing do not exceed the motor's
maximum operating temperature. Explosion-proof (or flame-proof) motors are used almost exclusively on drilling rigs.