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BASIC MOTOR fACTS

Irstwouldliketooutlinecertainactsaboutmotors. Motormanuacturersollowstandardsestablishedbythe

NationalElectricalManuacturersAssociation(NEMA).Tesestandardscoverthebasicdimensions,enclosures,andmini-mumperormanceratings.

TecommonsourceopowerintheUnitedStatesis60-hertz

alternatingcurrent(AC).TemotorsanddevicesdiscussedhereareonlyorACsystems.OutsidetheUnitedStatesthepowersourceis50Hz.Tetwoarenotinterchangeable.

Motorsareratedinhorsepower(hp)andspeedinrevolutionsperminute(rpm).

Motorsalsoareratedordutycycle.Amotorisratedcontinu-ousdutyiitoperatesatullloador60continuousminutesinany24-hourperiod.Motorsoperatinglessthanthatareratedintermittentduty,orashort-timerating.Tisisdonetocon-trolthetimethatcanelapsebeoreoverheatingoccurs.

Generally,singlephaseisusedtopowerportablemotorsandmotorsolessthan1hp.Amotor1hporlargerusuallyhasthree-phasepower.

Altitudeshigherthan3,300eetdepriveamotorosufcientcoolingair,whichmayleadtooverheating.ConsultNEMAorderatingguidelines.

MOTOR TYPES AND ENCLOSURES

Motorsareclassiedbythemethodusedtodissipateheat.AllmotortypesallintoNEMAgroupings,whicharebasedonmotorperormancecharacteristics.Tesecharacteristics arecurves otorqueandinrushcurrentasaunctionospeed.TevestandardNEMAclassicationsareA,B,C,D,andE.GroupEwasestab-lishedin2000toincludehighlyefcientmotors.Teenclosureoamotorreerstothearrangementotheventilatingopeningsor

othermeansorcoolingintheenvironmentinwhichthemoperates(seethesidebarorNEMAenclosureratings).Acommoneatureoallmotorsistheneedtostaycool.An

motorpermitsthepassageoexternalcoolingairoverandarthewindings.ItdoesnotpreventwaterromintrudingtheinteAnopendripproo(ODP)motorisintendedtobeusedinacdryenvironmentwhereacontinuousowoambientairthrthemotorsinternalpartswillkeepitcool.ODPmotorscandripsowaterromverticaluptoa15-degreeslant.Teventilopeningsareacedown.ODPisthemostcommonmotorustheconstructionindustry.Anothertypeomotorclassicatithe splash-proomotor, which oers urther protection agsplashing.otallyenclosedancooled(EFC)motorsareintended

usedindirty,dusty,andoutdoorenvironmentsandarecoolanexternalanmountedontheendoppositetheshat.Airnotmovethroughthemotor,sotheEFCtypeisidealordanddirtyenvironments.Teventilationopeningsarelocatethebottomothemotortopreventcondensationrombuiup.Tisisthesecond-mostcommonmotorused.

Atotallyenclosedairover(EAO)motorisusedmostly

ining,ventilation, andair-conditioning systems andsimilar

wheretheairstreampassesoverthemotorandcoolsit.Tistymotorusuallyisconnedtomanuacturersoriginalequipmotallyenclosednon-ventilated(ENV)motorsareusedi

toriessuchastextilemillswherelintandbersotherwisewadheretothemotorandreducecooling.Tistypeomotorallyis5hporlessanddependsonthesuraceareaothemenclosuretodissipatethegeneratedheat.Anencapsulatedmotorisanopenmotorinwhichthewin

arecoveredwithaheavycoatingomaterialtoprotectthemrommoisture,dirt,abrasion,andotherdifcultmaterials.

ElEctrical PrinciPlEsEvEry Plumbing EnginEEr should Know

me Fke, ciPE

All plumbing engineers should be acquainted with the basic principles oelectrical characteristics and accessories or speciying motors and motorpanel enclosures, as well as the environments in which certain motors can

be installed. In this article I will briefy review the types o motors and theselection o enclosures installed in both normal and hazardous locations tohelp plumbing industry proessionals better understand these systems.

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thiscompleteprotection,themotorotencanbeusedinapplica-tionsthatcalloratotallyenclosedmotor.Hazardouslocationmotors,sometimescalledexplosionproo,

aretotallyenclosedandmadeinconormancewithNationalElec-tricalCodeArticle500.Teyaredesignedandbuilttowithstandanexplosionodust,gas,orvaporandtopreventignitionoanygas,dust,orvaporsurroundingthemotortriggeredbysparks,ashes,orexplosionsthatmayoccurwithinthemotorenclosureitsel.

UNDERSTANDING CLASSES, GROUPS, AND DIvISIONS fOR

hAzARDOUS DUTY

oselectthepropermotororahazardouslocation,theengineermustbeawareothelistedmarkestablishedbytheUnderwritersLaboratory(UL)andthemeaningothetermsestablishedbytheNational ElectricalCode.Te area classicationhas three des-ignatorsclass,group, anddivisionwhichall shallbeworkedtogether.Teclassreerstothephysicalnatureothehazardousmaterial;thegroupreerstotheammabilitypotentialothemate-rial;andthedivisionreerstotheprobabilitythatahazardwill

exist. All hazardous locationmotorsmanuacturedater1975must carrya temperature code (-Code) thatidentiesthemaximumsuracetem-perature that could develop under

alloperatingconditionseverythingromoverloadtomotorburnout(seeable1).AClassIareacontainsammable

gasesorvaporswheretheyarestored,handled, processed, or transerred.Temotor is designed towithstandandconnetheeectsoaninternalmotorexplosion, aswell as tomeetthe surace temperature require-mentsunder bothnormaloperatingandault conditions.AClass IIareacontainscombustible dusts.AClassIIIareacontainseasilyignitablebers

oryingssuchassawdust,woodshavings,andtextilebers.Tegroupclassications, designatedA,B, C,D, E,F, andG,

separatematerialsaccording to theirammableand explosiveproperties.ClassIareashaveourgroups,A-D,andClassIIareashavethreegroups,E-G.ClassIIIhasnogroupsassociatedwithit.GroupA hasanatmospherecontainingacetylene,acolorless,

gaseoushydrocarbonchieyusedinorganicsynthesisandasauel(asinweldingandsoldering).GroupBhasanatmospherecontaininghydrogenorcombus-

tibleprocessgasesoequivalenthazardcontainingavolumeomore than 30 percent hydrogen, butadiene, acrolein, ethylene

oxide,orpropyleneoxide.GroupChasanatmospherecontainingethylene,ethylether,orgasesoequivalenthazard.GroupD has an atmosphere containing acetone, ammonia,

benzene,methane,ethane,butane,hexane,cyclopropane,natu-ralgas,naphtha,propane,orgasesoequivalenthazard.GroupEhasanatmospherecontainingcombustibleormetal

dusts such asaluminum,magnesium,and theiralloysorothercombustibledustswithaparticlesize,abrasiveness,andconduc-tivitythatpresentsimilarhazards.GroupFhasanatmospherecontainingcombustiblecarbona-

ceousdustssuchascarbonblack,charcoal,andcoalorduststhat

table 1 NEC Temperature Codes

MaximumOperating

Temperature T-CodeC F

450 842 T1300 572 T2

280 536 T2A

260 500 T2B

230 446 T2C

215 419 T2D

200 392 T3

180 356 T3A

165 329 T3B

160 320 T3C

135 275 T4

120 248 T4A

100 212 T5

85 185 T6

Source: National Electrical Code

NEMA CONTROL PANEL ENCLOSURESThe purpose o rating enclosures is to identiy the ability o

motors enclosure to resist external environmental inuences. Retance to everything rom dripping liquid to hose down to total smersion is defned in the rating system. The rating system is intendto provide inormation to help the engineer make appropriate setions.

NEMA 1: Enclosures designed to prevent accidental contact wenclosed apparatus. Suitable or indoor applications not exposedunusual service conditions. It will protect the electrical componein the enclosure rom alling dirt.

NEMA : Same as NEMA 1, but includes protection against dping and light splashing o liquids.

NEMA : Enclosures constructed or either indoor or outdoor and to prevent accidental contact with enclosed parts; to protagainst alling dirt, windblown dust, rain, sleet, and snow; and toundamaged by the external ormation o ice on the enclosure.

NEMA R: Same as NEMA 3, but excludes protection agawindblown dust.

NEMA S: Enclosures constructed or either indoor or outduse to prevent accidental contact with enclosed parts; to protthe enclosure rom the ingress o solid oreign objects such as alldirt, windblown dust, rain, sleet, and snow; and to allow an extermechanism(s) to remain operable with the ormation o ice on

enclosure.NEMA X: Same as NEMA 3S, but includes protection against c

rosion.NEMA RX: Same as NEMA 3X, but excludes protection aga

windblown dust.NEMA SX: Enclosures constructed or either indoor or outd

use to prevent accidental contact with enclosed parts and to ptect against the ingress o solid oreign objects such as alling dwindblown dust, rain, sleet, and snow. It will provide an additiolevel o protection against corrosion and also allow an extermechanism(s) to remain operable with the ormation o ice on enclosure.

NEMA : Enclosures constructed or either indoor or outdoor to prevent accidental contact with enclosed parts; to protect agathe ingress o solid oreign objects such as alling dirt, windblodust, rain, sleet, snow, splashing water, and hose-directed water; ato be undamaged by the external ormation o ice on the enclosu

NEMA X: Same as NEMA 4, but includes protection against crosion.

NEMA : Enclosures constructed or indoor use to prevent adental contact with enclosed hazardous parts and to protect agathe ingress o solid oreign objects such as alling dirt, settling dulint, fbers, and yings and the entry o water similar to light splaing and dripping.

NEMA : Enclosures constructed or either indoor or outdoor to prevent accidental contact with enclosed parts; to protect agathe ingress o solid oreign objects such as alling dirt and wa

similar to hose-directed water; and to be undamaged by ice on enclosure. The entry o water due to occasional temporary submsion to a limited depth is possible.

NEMA P: Same as NEMA 6, but includes protection agaicorrosion and the entry o water due to prolonged submersion tlimited depth.

NEMA : Enclosures constructed or indoor use in Class I, DivisI, Groups A, B, C, and D locations as defned in NFPA 70: National Etrical Code. Designed to meet National Electrical Code Class I. Tcircuit interruption occurs in air.

NEMA : Enclosures constructed or either indoor or outdoor uSimilar to NEMA 7, except the circuit interruption occurs in oil.

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havebeensensitizedbyothermaterialsandpresentanexplosionhazard.Group G has an atmosphere containing combustible dusts

notcoveredinClassesEandF,includingourandothergrains,woods,plastics,orchemicals.Hazardouslocationsaredividedintotwodivisions.ADivision

I locationis where ignitablesubstancesarelikely tobepresentcontinuously or intermittently during normal operations. Tisincludestank-llorventportsandlow-lyingareaswhereheavier-than-airvaporscouldaccumulate.A DivisionII locationisonewhere ignitable materials are handled or stored in a way thatwouldallowthemtoescapeintheeventoaaultsituationsuchasaspillorequipmentailure.TisalsoincludescloseproximitytoDivisionI.DivisionlocationsdonotappearinULlabelsorClassIorIImotorsbecauseallmotorsaredesignedtomeetDivisionIrequirementsandthereorearesuitableorbothtypesoloca-tions.

CONCLUSION

Selecting thepropermotor beginswithconsulting the insur-ance underwriter and the local code authorities.Tey are thesourcesordeterminingwhetheranarearequiresaDivisionIorIImotor.Nextdeterminetheclass,group,and-Codedependingonthetypeohazardpresent.Tengivethisinormationtothe

equipmentmanuacturer, alongwiththe physicalcharacteristicrequirements.Tesestepswillhelpensurethespecicationothepropermotororyourproject.

NEMA : Enclosures constructed or indoor use in Class I, DivisGroups E, F, and G locations.

NEMA 10: Enclosures that are permissible by the Mine SaetHealth Administration. Suitable or use in coal mines.

NEMA 1: Enclosures constructed or indoor use without kouts to prevent accidental contact with enclosed parts and to pagainst the ingress o solid oreign objects such as alling dirt, ciring fbers (airborne dust, lint, fbers, and yings) and the entry o similar to light splashing or dripping.

NEMA 1k. Same as NEMA 12, but includes enclosures constrwith knockouts.

NEMA 1: Enclosures constructed or indoor use with knockoprevent accidental contact with enclosed parts and to protect agthe ingress o solid oreign objects such as alling dirt, circulating(airborne dust, lint, fbers, and yings), the entry o water sim

Mike fRankeL has more than 45 years experience indesign and engineering of a variety of facilities, includingNASAs Vehicle Assembly Building in Cape Canaveral and Shrine of the Book in Israel. He is author of the Facility PipSystems Handbookas well as the plumbing sections of thArchitectural Graphic Standards and the Piping Handbook.For more information or to comment on this article, e -mrtcls@psdmgz.org.

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