motor enclosures

8/13/2019 Motor Enclosures

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Motor Enclosures: What You Need to KnowHydraulic Institute

An overview of the various descriptions of motor enclosures in North America, comparingthe enclosure descriptions in NEMA MG 1!""# and $E% &""#'()&""#'&, enclosures ine*plosion proof atmospheres, and other industr+ enclosure descriptions

-urpose

All electric motors (motors) have a housing that contains the working components of the motor. In

the U.S., the enclosure descries this housing. !he enclosure should meet specific environmental

re"uirements for restricting foreign o#ects, such as water, dust, and tools, and safety

re"uirements for personal protection. $epending upon the e%tent of containment, coolingconsiderations add to the design of the enclosure.

!ale &. Influences on the selection of type and design of motorenclosures.


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General Motor Enclosure %onsiderations

'hen selecting the correct motor enclosure, numerous considerations must e made for

determining the overall re"uirements of such enclosures. undamentally, these are governed y

three ma#or influences, which must then e analyed further ased on specific industry and

application variales. All resulting re"uirements are driven y the common need to safeguard the

functionality of the e"uipment and to protect oth personnel and environment. !heseconsiderations are summaried in !ale &.

NEMA .tandards MG 1!""#

!he *ational +lectrical anufacturers Association (*+A) provides a minimum standard for

general-purpose industrial A alternating current s"uirrel-cage induction motors. !his *+A

Standard is designated as / &-0112. 'ithin this standard, descriptions are provided for various

classifications of protection for motor enclosures in Section & - lassification According to

+nvironmental 3rotection and ethods of ooling.

*+A provides definitions for various motor enclosures. In general, there are two primarycategories - open and totally enclosed. An open motor has openings that allow e%ternal air to

pass over and around the motor windings that provides re"uired cooling. Although it is not

airtight, the enclosure of a totally enclosed motor limits cooling of the windings from the e%ternal

atmosphere. otor cooling for totally enclosed motors is typically done y some e%ternal means

such as a fan or water cooling. !ale 0 provides a summary of the *+A motor enclosure

definitions.

!ale 0. ommon *+A otor +nclosures.


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!he enclosure is selected depending upon the environment and cooling method in which the

motor will e operated. !he application environment will determine the degree of protection for

personal safety, water, or vapors. It is the responsiility of the purchaser to specify the motor

enclosure.

$E% /esignations

!he national standards of +urope and developing countries are, in general, ased on the

International +lectrotechnical ommission (I+). any of the motor re"uirements in their

applicale standards are similar to those of *+A. !he I+ standard has provided a more

detailed description of motor protection and how to conduct tests to determine the enclosure

designation. !hese classifications of degrees of protection have een included in the 0112

version of /-&.

%lassification of /egrees of -rotection -rovided 0+ Enclosures $- /esignations2

!he I+ designation for degrees of protection consist of the letters 4I4 and 434 followed y two

numerals. !he first represents the enclosure5s level of protection against incidental contact with

internal components. !he second defines the amount of water ingress that the enclosure must

protect. !his may e followed y a letter indicating whether the protection was tested dynamic (S)

or static (). *o letter indicates the motor will e operational under normal conditions to the

degree of protection designated.

!ale 2. Summary of I+ ode for $egree of3rotection.


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!ales 2 and 6 define the I3 designation

system. or e%ample, a motor with a $egree

of 3rotection of I3&2 would not allow

accidental contact with moving parts

e%ceeding &.789-in. (:1-mm) and would note adversely affected y a spray of water up

to 81-deg from vertical. I3 designations with

first numerals 6 or higher are typically used

when descriing totally enclosed machines.

/uards must also protect e%ternal fans to the degree of the motor enclosure and are tested in a

similar manner. or motors with an I32% or I36% enclosure that will e operated with open drain

holes, the drain hole may comply with the I30% protection re"uirements. or motors with an I3:%

enclosure that will e operated with open drain holes, the drain hole may comply with the I36%protection re"uirements.

Methods of %ooling $% /esignations2

!ale 6. Summary of I+ ode for ethods of ooling.


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+lectric motors must dissipate the heat

generated within their windings in order to

operate. If a unit fails to ade"uately cool

itself, it can overheat and cause damage to

itself and the driven e"uipment. !o guardagainst this damage, thermal protection

devices are availale that will trigger the

safe shutdown of a motor if the temperature

e%ceeds a predetermined ma%imum.

!here are varieties of cooling methods used in motor design. 'hen the cooling air is drawn from

the surrounding environment, circulated around the internal components, and e%pelled ack intothe surroundings, the cooling method is called anopen circuit. !his type of cooling is only

possile in open enclosure motors.

Closed circuit cooling involves internal coolant in a closed loop that passes heat to another

coolant either through the surface of the machine or a heat e%changer. !his type of cooling is y

definition associated with totally enclosed machines since the primary coolant remains contained

within the motor.

!ale :. omparison of *+A and I+ 3rotection$esignations.


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anormal condition.

!he locations are considered haardous ecause the atmosphere contains or may contain gas,

vapor, or dust in "uantities that may cause an e%plosion. ;nce the location is defined as

haardous, the location is further defined y the class and group of the haard. !he *ational+lectrical ode (*+) divides these locations into classes and groups according to the type of

haardous agent. !he following list has some of the agents in each classification. See Article :11

of the *ational +lectrical ode for a complete list.

lass I (/ases, >apors)

/roup A? Acetylene

/roup @? @utadiene, ethylene o%ide, hydrogen, propylene o%ide

/roup ? Acetaldehyde, cyclopropane, diethlether, ethylene, isoprene

/roup $? Acetone, acrylonitrile, ammonia, enene, utane, ethylene dichloride,

gasoline, he%ane, methane, methanol, naphtha, propane, propylene, styrene, toluene,

vinyl acetate, vinyl chloride, %ylene

lass II (omustile $usts)

/roup +? Aluminum, magnesium and other metal dusts with similar characteristics

/roup ? aron lack, coke or coal dust

/roup /? lour, starch or grain dust

A new +uropean directive, called the A!+ (A!mospheres +plosiles) directive, ecame

effective Buly 0112. !he directive, (76


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Corrosion duty

Industries with aggressive environments, such as high humidity or corrosiveC additional enclosure

features are re"uired for e%tended protection. !hese motors are typically !+ and have a

degree of protection of I3:6 via the use of a rotating shaft slinger. A higher degree of protectionvia the use of earing isolator(s) is also availale. Dotating slingers are provided to minimie

entrance of moisture and contaminants into the earing chamer. ondensation drain holes are

provided at the low points in the end rackets and are supplied with corrosion resistant reather

drain plugs. All fastening hardware is grade :, inc or cadmium plated. otor cast iron

components are typically o%ide primed and painted with vinyl-phenolic paint or other chemical

resistant paint. !his coating is chemical solvent, salt water and acid resistant. otor nameplate is

stainless steel.

Automotive duty

!he ma#or motor manufacturers have developed e%panded motor specifications that meet there"uirements of the manufacturing environment. !he frame sie (4U4 frame) is a previously used

*+A designation indicating frame sie and dimension (prior to &78: the standard frame sies

per horsepower rating).

ord Spec +&-&778 - !+ motors, which meets I+++ 96& frame, conduit o%, paint

and nameplate re"uirements.

/ Spec E+-&7E1 - !+ motors, cast iron frame and end rackets, steel or iron t-o%

with lead separator and gasket, shaft slinger.

Marine duty

or use on ships, a standard e%ists (I+++-6:) for motor drivers.

Aove $eck (waterproof)? A motor with corrosion duty construction with a shaft slinger on

the opposite pulley end. rame surface under conduit o% ase must e flat to ensure full

gasket fit and prevent water entry.

@elow $eck? orrosion treatment - consisting of anti-rust compounds on metal to metal

fits, plated hardware, epo%y painted aluminum parts and air deflectors, stainless steel

nameplate, resin and hardener or e"uivalent on rotor.

IEEE-841 standard - 1994

!hese motors are a cast iron, heavy duty, industrial design motor, intended for the chemical and

petroleum industries. ;ther industries, such as mining, food processing, pulp and paper, marine

and automotive industries also consider this construction ecause of the heavy-duty, reliale,

energy efficient design.

!he motors are !+ and have a degree of protection of I3:: on &62 to :9&& frames. otor

earings have a degree of protection of I3:: via the use of a non-contact earing isolator for


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!he motor is rated 911-hp (811-k') or greater for two-pole (2111-gpm or 2811-rpm)

machines of totally-enclosed construction, or rated &0:1-hp (721-k') or greater for two-

pole machines of open or guarded construction (including machines with '3-I or '3-II

type enclosures).

!he motor drives a high-inertia load (in e%cess of the load 'k0 listed in *+A /-& 3art

01). !he motor uses an ad#ustale speed drive as a source of power.

!he machine is an induction generator.

!he motor is a vertical machine rated :11-hp (2E:-k') or greater.

!he machine operates in anormally hostile environments.

! A-$ ('8 Generalpurpose 6ormwound .7uirrel %age $nduction Motors, !("hp and

larger

!his standard provides minimum re"uirements for form-wound s"uirrel cage induction motors that

are used in general-purpose petroleum, chemical and other industrial severe duty applications.

or motors larger than that descried and motors in other applications, they should e specified

in accordance with A3I Standard :6&. It is recommended that A3I Standard :6E is applied to

motors that have the following characteristics?

Dated 0:1-hp (&9:-k') through 2111-hp (00:1-k') for 6, 8 and 9 pole speeds.

Dated less than 911-hp (811-k') for two-pole (2111-rpm or 2811-rpm) motors of totally-

enclosed construction.

Dated less than &0:1-hp (721-k') for two-pole motors of '3-II type enclosures.

$rive centrifugal loads.

$rive loads having inertia values within those listed in *+A / & 3art 01.

Are not induction generators.

5ther $ssues

otor noise coming from motors is caused y a numer of variales, including the type of

enclosure and cooling, motor power sie, speed, and load conditions.

or totally enclosed motors utiliing fans for cooling, the air turulence produced y the cooling

fan can create the greatest amount of noise, especially at 0-pole speeds. As larger motors may

re"uire higher cooling, larger cooling fans are re"uired, developing greater air flow and more

noise. As motor speeds are decreased, less air turulence is created, which can reduce the noise

developed.

;ther e%ternal methods of noise reductions can e used. +%ternal enclosures with noise

insulating material are used to reduce the noise. Although these can e effective in noise

reduction, they can impact the effectiveness of the enclosure (especially with cooling) or make

the enclosure sustantially larger.


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motor enclosures

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