11
Power Supply and Wiring
Section 6 (continued)
ToremovethelinetogroundMOVprotection,locatethejumpershownbelow.Thejumperislocatedbetween
theinputandoutputterminalblocksonthemainboard.Movetothepositionshown.
 ForFrameSize1Controllers: ForFrameSizes2and3Controllers:
Resistance grounding and ground fault protection
ConnectingtheWyesecondaryneutraltogroundthrougharesistorisanacceptablemethodofgrounding.
Underashortcircuitsecondarycondition,anyoftheoutputphasestogroundwillnotexceedthenormal
linetolinevoltage.ThisiswithintheratingoftheMOVinputprotectiondevicesonthedrive.Theresistoris
oftenusedtodetectgroundcurrentbymonitoringtheassociatedvoltagedrop.Sincehighfrequencyground
currentcanowthroughthisresistor,careshouldbetakentoproperlyconnectthedrivemotorleadsusing
therecommendedcablesandmethods.Insomecases,multipledrivesononetransformercanproducea
cumulativegroundcurrentthatcantriggerthegroundfaultinterruptcircuit.
Open Delta (consult factory)
Thistypeofcongurationiscommonon230voltsystems.Fromtimetotimeitmaybeencounteredwhere
onlysinglephasepowerisavailableandthree-phasepowerisrequired.Thetechniqueusestwosinglephase
transformerstoderiveathirdphase.Whenusedtopoweradrivethiscongurationmustbe���deratedtoabout
70%ofthesinglephaseratingofonetransformer.Thissystemprovidespoorregulationanditispossiblethat
onlythetwolineconnectedphaseswillprovidepower.Inthiscasethedrivemustbederatedto50%ofits
rating.(Ex.A20HP230voltdrivenowbecomesa10HP230voltdrive.)